{"id":461,"date":"2021-12-17T21:45:35","date_gmt":"2021-12-17T21:45:35","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/6-metamorphic-rocks\/"},"modified":"2025-01-21T01:03:28","modified_gmt":"2025-01-21T01:03:28","slug":"6-metamorphic-rocks","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/6-metamorphic-rocks\/","title":{"raw":"6 Metamorphic Rocks","rendered":"6 Metamorphic Rocks"},"content":{"raw":"[caption id=\"attachment_3142\" align=\"aligncenter\" width=\"1024\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/BCG3-scaled.jpg\"><img class=\"wp-image-3142 size-large\" title=\"By Matt Affolter\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2021\/12\/BCG3-scaled-1.jpg\" alt=\"The painted wall is a large cliff\" width=\"1024\" height=\"768\"><\/a> Painted Wall of Black Canyon of the Gunnison National Park, Colorado, made of 1.7 billion-year old gneiss intruded by younger pegmatites.[\/caption]\n<h1>6 Metamorphic Rocks<\/h1>\n<em>Contributing Author: Dr. Peter Davis, Pacific Lutheran University<\/em>\n\n<b>KEY CONCEPTS<\/b>\n<ul>\n \t<li>Describe the [pb_glossary id=\"2689\"]temperature[\/pb_glossary] and pressure conditions of the [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] environment<\/li>\n \t<li>Identify and describe the three principal [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] agents<\/li>\n \t<li>Describe what [pb_glossary id=\"2920\"]recrystallization[\/pb_glossary] is and how it affects [pb_glossary id=\"2687\"]mineral[\/pb_glossary] crystals<\/li>\n \t<li>Explain what [pb_glossary id=\"2924\"]foliation[\/pb_glossary] is and how it results from directed pressure and [pb_glossary id=\"2920\"]recrystallization[\/pb_glossary]<\/li>\n \t<li>Explain the relationships among [pb_glossary id=\"2926\"]slate[\/pb_glossary], [pb_glossary id=\"2928\"]phyllite[\/pb_glossary], [pb_glossary id=\"2929\"]schist[\/pb_glossary], and [pb_glossary id=\"2932\"]gneiss[\/pb_glossary] in terms of metamorphic grade<\/li>\n \t<li>Define [pb_glossary id=\"2939\"]index mineral[\/pb_glossary]<\/li>\n \t<li>Explain how [pb_glossary id=\"2942\"]metamorphic facies[\/pb_glossary] relate to [pb_glossary id=\"2591\"]plate[\/pb_glossary] [pb_glossary id=\"2576\"]tectonic[\/pb_glossary] processes<\/li>\n \t<li>Describe what a contact [pb_glossary id=\"2945\"]aureole[\/pb_glossary] is and how [pb_glossary id=\"2944\"]contact metamorphism[\/pb_glossary] affects surrounding rock<\/li>\n \t<li>Describe the role of [pb_glossary id=\"2921\"]hydrothermal[\/pb_glossary] [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary] in forming [pb_glossary id=\"2687\"]mineral[\/pb_glossary] deposits and [pb_glossary id=\"3325\"]ore[\/pb_glossary] bodies<\/li>\n<\/ul>\n[caption id=\"attachment_2480\" align=\"alignright\" width=\"379\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/Fig-6-1.jpg\"><img class=\"wp-image-46\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig-6-1-300x278.jpg\" alt=\"The rock cycle shows how different rock groups are interconnected. Metamorphic rocks can come from adding heat and\/or pressure to other metamorphic rock or sedimentary or igneous rocks\" width=\"379\" height=\"352\"><\/a> Rock cycle showing the five materials (such as igneous rocks and sediment) and the processes by which one changes into another (such as weathering). (Source: Peter Davis)[\/caption]\n\n<strong>[pb_glossary id=\"2914\"]Metamorphic[\/pb_glossary] rocks<\/strong>, <em>meta-<\/em> meaning change and -<em>morphos<\/em>&nbsp;meaning form, is one of the three rock categories in the [pb_glossary id=\"2671\"]rock cycle[\/pb_glossary] (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/1-understanding-science\/\">Chapter 1<\/a>). [pb_glossary id=\"2684\"]Metamorphic rock[\/pb_glossary] material has been changed by [pb_glossary id=\"2689\"]temperature[\/pb_glossary], pressure, and\/or fluids. <span style=\"font-weight: 400\">The [pb_glossary id=\"2671\"]rock cycle[\/pb_glossary] shows that both [pb_glossary id=\"2675\"]igneous[\/pb_glossary] and sedimentary rocks can become [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] rocks. And [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] rocks themselves&nbsp; can be re-metamorphosed. <\/span>Because [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary] is caused by [pb_glossary id=\"2576\"]plate tectonic[\/pb_glossary] motion, [pb_glossary id=\"2684\"]metamorphic rock[\/pb_glossary] provides geologists with a history book of how past [pb_glossary id=\"2576\"]tectonic[\/pb_glossary] processes shaped our planet.\n<h2><span style=\"font-weight: 400\">6.1 Metamorphic Processes<\/span><\/h2>\n[pb_glossary id=\"2914\"]Metamorphism[\/pb_glossary] occurs when solid rock changes in [pb_glossary id=\"2831\"]composition[\/pb_glossary] and\/or [pb_glossary id=\"2919\"]texture[\/pb_glossary] without the [pb_glossary id=\"2687\"]mineral[\/pb_glossary] crystals melting, which is how [pb_glossary id=\"2675\"]igneous rock[\/pb_glossary] is generated. [pb_glossary id=\"2914\"]Metamorphic[\/pb_glossary] [pb_glossary id=\"3340\"]source rocks[\/pb_glossary], the rocks that experience the [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary], are called the [pb_glossary id=\"2688\"]parent rock[\/pb_glossary] or <strong>[pb_glossary id=\"2688\"]protolith[\/pb_glossary]<\/strong>, from <em>proto<\/em>- meaning first, and <em>lithos- <\/em>meaning rock. Most [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] processes take place deep underground, inside the earth\u2019s [pb_glossary id=\"2580\"]crust[\/pb_glossary]. During [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary], [pb_glossary id=\"2688\"]protolith[\/pb_glossary] chemistry is mildly changed by increased [pb_glossary id=\"2689\"]temperature[\/pb_glossary] (heat), a type of pressure called [pb_glossary id=\"2917\"]confining[\/pb_glossary] pressure, and\/or chemically reactive fluids. Rock [pb_glossary id=\"2919\"]texture[\/pb_glossary] is changed by heat, [pb_glossary id=\"2917\"]confining[\/pb_glossary] pressure, and a type of pressure called [pb_glossary id=\"2918\"]directed stress[\/pb_glossary].\n<h3><span style=\"font-weight: 400\">6.1.1&nbsp; Temperature (Heat) &nbsp;<\/span><\/h3>\n[pb_glossary id=\"2689\"]Temperature[\/pb_glossary] measures a substance\u2019s energy\u2014an increase in [pb_glossary id=\"2689\"]temperature[\/pb_glossary] represents an increase in energy. [pb_glossary id=\"2689\"]Temperature[\/pb_glossary] changes affect the chemical equilibrium or [pb_glossary id=\"2702\"]cation[\/pb_glossary] balance in [pb_glossary id=\"2687\"]minerals[\/pb_glossary]. At high temperatures atoms may vibrate so vigorously they jump from one position to another within the crystal lattice, which remains intact. In other words, this atom swapping can happen while the rock is still solid.\n\nThe temperatures of [pb_glossary id=\"2684\"]metamorphic rock[\/pb_glossary] lies in between surficial processes (as in [pb_glossary id=\"2683\"]sedimentary rock[\/pb_glossary]) and [pb_glossary id=\"2672\"]magma[\/pb_glossary] in the [pb_glossary id=\"2671\"]rock cycle[\/pb_glossary]. Heat-driven [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary] begins at temperatures as cold as 200\u02daC, and can continue to occur at temperatures as high as 700\u00b0C-1,100\u00b0C. Higher temperatures would create [pb_glossary id=\"2672\"]magma[\/pb_glossary], and thus, would no longer be a [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] process.&nbsp;[pb_glossary id=\"2689\"]Temperature[\/pb_glossary] increases with increasing depth in the Earth along a [pb_glossary id=\"1175\"]geothermal gradient[\/pb_glossary] (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/4-igneous-processes-and-volcanoes\/\">Chapter 4<\/a>) and [pb_glossary id=\"2684\"]metamorphic rock[\/pb_glossary] records these depth-related [pb_glossary id=\"2689\"]temperature[\/pb_glossary] changes.\n<h3><span style=\"font-weight: 400\">6.1.2 Pressure<\/span><\/h3>\nPressure <span style=\"font-weight: 400\">is the force exerted over a unit area on a material. Like heat, pressure can affect the chemical equilibrium of [pb_glossary id=\"2687\"]minerals[\/pb_glossary] in a rock. The pressure that affects [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] rocks can be grouped into [pb_glossary id=\"2917\"]confining[\/pb_glossary] pressure and [pb_glossary id=\"2918\"]directed stress[\/pb_glossary]. <strong>[pb_glossary id=\"2915\"]Stress[\/pb_glossary]<\/strong> is a scientific term indicating a&nbsp;force. <strong>[pb_glossary id=\"2916\"]Strain[\/pb_glossary]<\/strong> is the result of this [pb_glossary id=\"2915\"]stress[\/pb_glossary], including [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] changes within [pb_glossary id=\"2687\"]minerals[\/pb_glossary].<\/span>\n<h4><b>Confining Pressure<\/b><\/h4>\n[caption id=\"attachment_3148\" align=\"alignright\" width=\"450\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.1-02-Pressure-vs-Stress.png\"><img class=\"wp-image-432\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.1-02-Pressure-vs-Stress-300x252.png\" alt=\"Pressure is a state where all stresses on a body are equal. The magnitude of these balanced stresses increases with increasing depth within the earth. These stresses can not deform rocks other than to decrease their volume. Pressure is the term used becuase the concept of pressure is used in chemistry, which it the discipline of science used to understand the mineral reactions that occur within the rock. DIRECTED STRESSES s, s, One or more directions of stress are not equal in magnitude and or not in line with each other (non-coaxial). Unlike balanced stresses, the difference in these stresses can deform rocks within the earth.\" width=\"450\" height=\"378\"><\/a> Difference between pressure and stress and how they deform rocks. Pressure (or confining pressure) has equal stress (forces) in all directions and increases with depth under the Earth\u2019s surface. Under directed stress, some stress directions (forces) are stronger than others, and this can deform rocks. (Source: Peter Davis)[\/caption]\n\n<span style=\"font-weight: 400\">Pressure exerted on rocks under the surface&nbsp;is due to the simple fact that rocks lie on top of one another. When pressure is exerted from rocks above, it is balanced from below and sides, and is called <\/span><b>[pb_glossary id=\"2917\"]confining[\/pb_glossary]<\/b><span style=\"font-weight: 400\"> or <\/span><b>[pb_glossary id=\"2917\"]lithostatic[\/pb_glossary] pressure<\/b><span style=\"font-weight: 400\">. [pb_glossary id=\"2917\"]Confining[\/pb_glossary] pressure has equal pressure on all sides (see figure) and is&nbsp;responsible for causing chemical reactions to occur just like heat. These chemical reactions will cause new [pb_glossary id=\"2687\"]minerals[\/pb_glossary] to form.&nbsp;<\/span>\n\n<span style=\"font-weight: 400\">[pb_glossary id=\"2917\"]Confining[\/pb_glossary] pressure is measured in bars and ranges from 1 bar at sea level to around 10,000 bars at the base of the [pb_glossary id=\"2580\"]crust[\/pb_glossary]. &nbsp;For [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] rocks, pressures range from a relatively low-pressure of 3,000 bars around 50,000 bars, which occurs around 15-35 kilometers below the surface.<\/span>\n<h4><b>Directed Stress<\/b><\/h4>\n[caption id=\"attachment_3150\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2_800px-P535973.jpg\"><img class=\"wp-image-433 size-medium\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2_800px-P535973-300x225.jpg\" alt=\"Pebbles in quartzite deformed by directed stress\" width=\"300\" height=\"225\"><\/a> Pebbles (that used to be spherical or close to spherical) in quartzite deformed by directed stress[\/caption]\n\n<strong>[pb_glossary id=\"2918\"]Directed stress[\/pb_glossary]<\/strong>, also called differential or [pb_glossary id=\"2918\"]tectonic stress[\/pb_glossary], is an unequal balance of forces on a rock in one or more directions (see previous figure). Directed [pb_glossary id=\"2915\"]stresses[\/pb_glossary] are generated by the movement of lithospheric [pb_glossary id=\"2591\"]plates[\/pb_glossary]. [pb_glossary id=\"2915\"]Stress[\/pb_glossary] indicates a type of force acting on rock. [pb_glossary id=\"2916\"]Strain[\/pb_glossary] describes the resultant processes caused by [pb_glossary id=\"2915\"]stress[\/pb_glossary] and includes [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] changes in the [pb_glossary id=\"2687\"]minerals[\/pb_glossary]. In contrast to [pb_glossary id=\"2917\"]confining[\/pb_glossary] pressure, [pb_glossary id=\"2918\"]directed stress[\/pb_glossary] occurs at much lower pressures and does not generate chemical reactions that change [pb_glossary id=\"2687\"]mineral[\/pb_glossary] [pb_glossary id=\"2831\"]composition[\/pb_glossary] and atomic structure. Instead, [pb_glossary id=\"2918\"]directed stress[\/pb_glossary] modifies the [pb_glossary id=\"2688\"]parent rock[\/pb_glossary] at a mechanical level, changing the arrangement, size, and\/or shape of the [pb_glossary id=\"2687\"]mineral[\/pb_glossary] crystals. These crystalline changes create identifying textures, which is shown in the figure below comparing the [pb_glossary id=\"1940\"]phaneritic[\/pb_glossary] [pb_glossary id=\"2919\"]texture[\/pb_glossary] of [pb_glossary id=\"2675\"]igneous[\/pb_glossary] [pb_glossary id=\"1962\"]granite[\/pb_glossary] with the [pb_glossary id=\"2924\"]foliated[\/pb_glossary] [pb_glossary id=\"2919\"]texture[\/pb_glossary] of [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] [pb_glossary id=\"2932\"]gneiss[\/pb_glossary].\n\n[caption id=\"attachment_3152\" align=\"aligncenter\" width=\"1024\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.1-03-Granite-vs-Gneiss.jpg\"><img class=\"wp-image-434 size-large\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.1-03-Granite-vs-Gneiss-1024x443.jpg\" alt=\"Two rocks with very similar colors. One is a granite and another is a gneiss that has aligned dark minerals.\" width=\"1024\" height=\"443\"><\/a> An igneous rock granite (left) and foliated high-temperature and high-pressure metamorphic rock gneiss (right) illustrating a metamorphic texture. (Source: Peter Davis)[\/caption]\n\nDirected [pb_glossary id=\"2915\"]stresses[\/pb_glossary] produce rock textures in many ways. Crystals are rotated, changing their orientation in space. Crystals can get fractured, reducing their [pb_glossary id=\"2828\"]grain size[\/pb_glossary]. Conversely, they may grow larger as atoms migrate. Crystal shapes also become deformed. These mechanical changes occur via <strong>[pb_glossary id=\"2920\"]recrystallization[\/pb_glossary]<\/strong>, which is when [pb_glossary id=\"2687\"]minerals[\/pb_glossary] [pb_glossary id=\"2815\"]dissolve[\/pb_glossary] from an area of rock experiencing high [pb_glossary id=\"2915\"]stress[\/pb_glossary] and [pb_glossary id=\"2707\"]precipitate[\/pb_glossary] or regrow in a location having lower [pb_glossary id=\"2915\"]stress[\/pb_glossary]. For example, [pb_glossary id=\"2920\"]recrystallization[\/pb_glossary] increases [pb_glossary id=\"2828\"]grain size[\/pb_glossary] much like adjacent soap bubbles coalesce to form larger ones. [pb_glossary id=\"2920\"]Recrystallization[\/pb_glossary] rearranges [pb_glossary id=\"2687\"]mineral[\/pb_glossary] crystals without fracturing the rock structure, deforming the rock like silly putty; these changes provide important clues to understanding the creation and movement of deep underground rock [pb_glossary id=\"3065\"]faults[\/pb_glossary].\n<h3><span style=\"font-weight: 400\">6.1.3 Fluids<\/span><\/h3>\nA third [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] agent is chemically reactive fluids that are expelled by crystallizing [pb_glossary id=\"2672\"]magma[\/pb_glossary] and created by [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] reactions. These reactive fluids are made of mostly water (H<sub>2<\/sub>O) and carbon dioxide (CO<sub>2<\/sub>), and smaller amounts of potassium (K), sodium (Na), iron (Fe), magnesium (Mg), calcium (Ca), and aluminum (Al). These fluids react with [pb_glossary id=\"2687\"]minerals[\/pb_glossary] in the [pb_glossary id=\"2688\"]protolith[\/pb_glossary], changing its chemical equilibrium and [pb_glossary id=\"2687\"]mineral[\/pb_glossary] [pb_glossary id=\"2831\"]composition[\/pb_glossary], in a process similar to the reactions driven by heat and pressure. In addition to using [pb_glossary id=\"2700\"]elements[\/pb_glossary] found in the [pb_glossary id=\"2688\"]protolith[\/pb_glossary], the chemical reaction may incorporate substances contributed by the fluids to create new [pb_glossary id=\"2687\"]minerals[\/pb_glossary]. In general, this style of [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary], in which fluids play an important role, is called <strong>[pb_glossary id=\"2921\"]hydrothermal[\/pb_glossary] [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary]<\/strong> or [pb_glossary id=\"2921\"]hydrothermal[\/pb_glossary] alteration. Water actively participates in chemical reactions and allows extra mobility of the components in [pb_glossary id=\"2921\"]hydrothermal[\/pb_glossary] alteration.\n\nFluids-activated [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary] is frequently involved in creating economically important [pb_glossary id=\"2687\"]mineral[\/pb_glossary] deposits that are located next to [pb_glossary id=\"2675\"]igneous[\/pb_glossary] intrusions or [pb_glossary id=\"2672\"]magma[\/pb_glossary] bodies. For example, the [pb_glossary id=\"3324\"]mining[\/pb_glossary] districts in the Cottonwood Canyons and [pb_glossary id=\"2687\"]Mineral[\/pb_glossary] [pb_glossary id=\"1461\"]Basin[\/pb_glossary] of northern Utah produce valuable [pb_glossary id=\"3325\"]ores[\/pb_glossary] such as argentite (silver [pb_glossary id=\"1921\"]sulfide[\/pb_glossary]), galena (lead [pb_glossary id=\"1921\"]sulfide[\/pb_glossary]), and chalcopyrite (copper iron [pb_glossary id=\"1921\"]sulfide[\/pb_glossary]), as well as the [pb_glossary id=\"1924\"]native[\/pb_glossary] [pb_glossary id=\"2700\"]element[\/pb_glossary] gold. These [pb_glossary id=\"2687\"]mineral[\/pb_glossary] deposits were created from the interaction between a granitic intrusion called the Little Cottonwood Stock and [pb_glossary id=\"1971\"]country rock[\/pb_glossary] consisting of mostly [pb_glossary id=\"2851\"]limestone[\/pb_glossary] and dolostone. Hot, circulating fluids expelled by the crystallizing [pb_glossary id=\"1962\"]granite[\/pb_glossary] reacted with and [pb_glossary id=\"2815\"]dissolved[\/pb_glossary] the surrounding [pb_glossary id=\"2851\"]limestone[\/pb_glossary] and dolostone, precipitating out new [pb_glossary id=\"2687\"]minerals[\/pb_glossary] created by the chemical reaction. [pb_glossary id=\"2921\"]Hydrothermal[\/pb_glossary] alternation of [pb_glossary id=\"1956\"]mafic[\/pb_glossary] [pb_glossary id=\"2586\"]mantle[\/pb_glossary] rock, such as [pb_glossary id=\"2711\"]olivine[\/pb_glossary] and [pb_glossary id=\"1961\"]basalt[\/pb_glossary], creates the [pb_glossary id=\"2684\"]metamorphic rock[\/pb_glossary] <strong>[pb_glossary id=\"2923\"]serpentinite[\/pb_glossary]<\/strong>, a member of the serpentine subgroup of [pb_glossary id=\"2687\"]minerals[\/pb_glossary]. This [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] process happens at mid-ocean [pb_glossary id=\"2630\"]spreading centers[\/pb_glossary] where newly formed [pb_glossary id=\"2581\"]oceanic crust[\/pb_glossary] interacts with seawater.\n\n[caption id=\"attachment_2545\" align=\"alignright\" width=\"304\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/BlackSmoker.jpg\">&lt;img class=\"wp-image-2545\" title=\"By University of Washington; NOAA\/OAR\/OER. (NOAA Photo Library: expl2366) [<a href=\"\/\/creativecommons.org\/licenses\/by\/2.0&quot;\">CC BY 2.0<\/a> or Public domain], <a href=\"\/\/commons.wikimedia.org\/wiki\/File%3AExpl2366_-_Flickr_-_NOAA_Photo_Library.jpg&quot;\">via Wikimedia Commons<\/a>\" src=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/BlackSmoker-233x300.jpg\" alt=\"There is a large build up of minerals around the vent\" width=\"304\" height=\"392\"&gt;<\/a> Black smoker hydrothermal vent with a colony of giant (6\u2019+) tube worms.[\/caption]Some [pb_glossary id=\"2921\"]hydrothermal[\/pb_glossary] alterations remove [pb_glossary id=\"2700\"]elements[\/pb_glossary] from the [pb_glossary id=\"2688\"]parent rock[\/pb_glossary] rather than deposit them. This happens when seawater circulates down through [pb_glossary id=\"1934\"]fractures[\/pb_glossary] in the fresh, still-hot [pb_glossary id=\"1961\"]basalt[\/pb_glossary], reacting with and removing [pb_glossary id=\"2687\"]mineral[\/pb_glossary] ions from it. The [pb_glossary id=\"2815\"]dissolved[\/pb_glossary] [pb_glossary id=\"2687\"]minerals[\/pb_glossary] are usually ions that do not fit snugly in the [pb_glossary id=\"2709\"]silicate[\/pb_glossary] crystal structure, such as copper. The [pb_glossary id=\"2687\"]mineral[\/pb_glossary]-laden water emerges from the sea floor via [pb_glossary id=\"2921\"]hydrothermal[\/pb_glossary] vents called <strong>[pb_glossary id=\"2922\"]black smokers[\/pb_glossary]<\/strong>, named after the dark-colored precipitates produced when the hot [pb_glossary id=\"1187\"]vent[\/pb_glossary] water meets cold seawater. (see Chapter 4, [pb_glossary id=\"2675\"]Igneous Rock[\/pb_glossary] and [pb_glossary id=\"1181\"]Volcanic[\/pb_glossary] Processes) Ancient [pb_glossary id=\"2922\"]black smokers[\/pb_glossary] were an important source of copper [pb_glossary id=\"3325\"]ore[\/pb_glossary] for the inhabitants of Cyprus (Cypriots) as early as 4,000 BCE, and later by the Romans.\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"37\"]\n\n[caption id=\"attachment_4000\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/6.1-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-435\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/6.1-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 6.1 via this QR Code.[\/caption]\n<h2><span style=\"font-weight: 400\">6.2 Metamorphic textures <\/span><\/h2>\n<span style=\"font-weight: 400\">[pb_glossary id=\"2914\"]Metamorphic[\/pb_glossary] [pb_glossary id=\"2919\"]texture[\/pb_glossary] is the description of the shape and orientation of [pb_glossary id=\"2687\"]mineral[\/pb_glossary] grains in a [pb_glossary id=\"2684\"]metamorphic rock[\/pb_glossary]. [pb_glossary id=\"2684\"]Metamorphic rock[\/pb_glossary] textures are [pb_glossary id=\"2924\"]foliated[\/pb_glossary], [pb_glossary id=\"2934\"]non-foliated[\/pb_glossary], or lineated are described below.<\/span>\n\n[caption id=\"attachment_3157\" align=\"aligncenter\" width=\"791\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/MetaRx3.png\"><img class=\"wp-image-436 size-large\" title=\"(Source: Belinda Madsen) SLCC\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/MetaRx3-791x1024.png\" alt=\"Table identifying the types of metamorphic rocks.\" width=\"791\" height=\"1024\"><\/a> Metamorphic rock identification table. (Source: Belinda Madsen)[\/caption]\n<h3><span style=\"font-weight: 400\">6.2.1 Foliation and Lineation<\/span><\/h3>\n<span style=\"font-weight: 400\"><strong>[pb_glossary id=\"2924\"]Foliation[\/pb_glossary]<\/strong> is a term used that describes [pb_glossary id=\"2687\"]minerals[\/pb_glossary] lined up in planes. Certain [pb_glossary id=\"2687\"]minerals[\/pb_glossary], most notably the [pb_glossary id=\"1914\"]mica[\/pb_glossary] group, are mostly thin and planar by default. [pb_glossary id=\"2924\"]Foliated[\/pb_glossary] rocks typically appear as if the [pb_glossary id=\"2687\"]minerals[\/pb_glossary] are stacked like pages of a book, thus the use of the term \u2018folia\u2019, like a leaf<\/span><span style=\"font-weight: 400\">. Other [pb_glossary id=\"2687\"]minerals[\/pb_glossary], with hornblende being a good example, are longer in one direction, linear like a pencil or a needle, rather than a planar-shaped book. These linear objects can also be aligned within a rock. This is referred to as a <\/span><b>[pb_glossary id=\"2925\"]lineation[\/pb_glossary]<\/b><span style=\"font-weight: 400\">. Linear crystals, such as hornblende, tourmaline, or stretched [pb_glossary id=\"1915\"]quartz[\/pb_glossary] grains, can be arranged as part of a [pb_glossary id=\"2924\"]foliation[\/pb_glossary], a [pb_glossary id=\"2925\"]lineation[\/pb_glossary], or [pb_glossary id=\"2924\"]foliation[\/pb_glossary]\/[pb_glossary id=\"2925\"]lineation[\/pb_glossary] together. If they lie on a plane with [pb_glossary id=\"1914\"]mica[\/pb_glossary], but with no common or preferred direction, this is [pb_glossary id=\"2924\"]foliation[\/pb_glossary]. If the [pb_glossary id=\"2687\"]minerals[\/pb_glossary] line up and point in a common direction, but with no planar fabric, this is [pb_glossary id=\"2925\"]lineation[\/pb_glossary]. When [pb_glossary id=\"2687\"]minerals[\/pb_glossary] lie on a plane AND point in a common direction; this is both [pb_glossary id=\"2924\"]foliation[\/pb_glossary] and [pb_glossary id=\"2925\"]lineation[\/pb_glossary]. &nbsp;<\/span>\n\n[caption id=\"attachment_3164\" align=\"aligncenter\" width=\"588\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-06-Lineation.png\"><img class=\"wp-image-437\" title=\"Source: Peter Davis, Pacific Lutheran University\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-06-Lineation-300x162.png\" alt=\"Lineation is aligned linear features in a rock. An example in the figure is a bundle of aligned straws.\" width=\"588\" height=\"318\"><\/a> Example of lineation where minerals are aligned like a stack of straws or pencils. (Source: Peter Davis)[\/caption]\n\n[caption id=\"attachment_3165\" align=\"aligncenter\" width=\"563\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-05-Foliationlineation.jpg\"><img class=\"wp-image-438\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-05-Foliationlineation-300x113.jpg\" alt=\"Aligned tourmaline crystals in line with foliation. Foliation is the fine &quot;layers&quot; of the rock.\" width=\"563\" height=\"213\"><\/a> An example of foliation WITH lineation. (Source: Peter Davis)[\/caption]\n\n[caption id=\"attachment_3167\" align=\"aligncenter\" width=\"538\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-04-Foliation-without-lineation.png\"><img class=\"wp-image-439\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-04-Foliation-without-lineation-300x222.png\" alt=\"Foliated surface displays non-lineated hornblende grains. A cross-section displays a cross section of foliated plagioclase and hornblende\" width=\"538\" height=\"399\"><\/a> An example of foliation WITHOUT lineation. (Source: Peter Davis)[\/caption]\n\n[pb_glossary id=\"2924\"]Foliated[\/pb_glossary] [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] rocks are named based on the style of their foliations. Each rock name has a specific [pb_glossary id=\"2919\"]texture [\/pb_glossary] that defines and distinguishes it, with their descriptions listed below.\n\n<b>[pb_glossary id=\"2926\"]Slate[\/pb_glossary]<\/b><span style=\"font-weight: 400\"> is a fine-grained [pb_glossary id=\"2684\"]metamorphic rock[\/pb_glossary] that exhibits a [pb_glossary id=\"2924\"]foliation[\/pb_glossary] called <\/span><b>[pb_glossary id=\"2927\"]slaty cleavage[\/pb_glossary] <\/b><span style=\"font-weight: 400\">that is the flat orientation of the small platy crystals of [pb_glossary id=\"1914\"]mica[\/pb_glossary] and chlorite forming perpendicular to the direction of [pb_glossary id=\"2915\"]stress[\/pb_glossary]<\/span><i><span style=\"font-weight: 400\">.&nbsp;<\/span><\/i><span style=\"font-weight: 400\">The [pb_glossary id=\"2687\"]minerals[\/pb_glossary] in [pb_glossary id=\"2926\"]slate[\/pb_glossary] are too small to see with the unaided eye. The thin layers in [pb_glossary id=\"2926\"]slate[\/pb_glossary] may resemble sedimentary [pb_glossary id=\"2857\"]bedding[\/pb_glossary], but they are a result of [pb_glossary id=\"2918\"]directed stress[\/pb_glossary] and may lie at angles to the original [pb_glossary id=\"2857\"]strata[\/pb_glossary]. In fact, original sedimentary layering may be partially or completely obscured by the [pb_glossary id=\"2924\"]foliation[\/pb_glossary]. Thin slabs of [pb_glossary id=\"2926\"]slate[\/pb_glossary] are often used as a building material for roofs and tiles.<\/span>\n\n[caption id=\"attachment_3169\" align=\"aligncenter\" width=\"383\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-Ehemaliger_Schiefertagebau_am_Brand.jpg\">&lt;img class=\"wp-image-3169\" title=\"By Uta Baumfelder at de.wikipedia (Own work) [Public domain], <a href=\"\/\/commons.wikimedia.org\/wiki\/File%3AEhemaliger_Schiefertagebau_am_Brand.JPG&quot;\">via Wikimedia Commons<\/a>\" src=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-Ehemaliger_Schiefertagebau_am_Brand-300x225.jpg\" alt=\"Rock breaking along flat even planes.\" width=\"383\" height=\"287\"&gt;<\/a> Slate mine in Germany cleavage.[\/caption]\n\n[caption id=\"attachment_3171\" align=\"aligncenter\" width=\"420\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-07-Foliation-vs-bedding.jpg\"><img class=\"wp-image-440\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-07-Foliation-vs-bedding-300x200.jpg\" alt=\"Foliation is caused by metamorphism. Bedding is a result of sedimentary processes. They do not have to align.\" width=\"420\" height=\"280\"><\/a> Foliation vs. bedding. Foliation is caused by metamorphism. Bedding is a result of sedimentary processes. They do not have to align. (Source: Peter Davis)[\/caption]\n\n[caption id=\"attachment_3174\" align=\"alignright\" width=\"377\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-10-Phyllite-with-fold-scaled.jpg\"><img class=\"wp-image-3174\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-10-Phyllite-with-fold-scaled-1.jpg\" alt=\"A foliated rock with a slight sheen.\" width=\"377\" height=\"283\"><\/a> Phyllite with a small fold. (Source: Peter Davis)[\/caption]\n\n<b>[pb_glossary id=\"2928\"]Phyllite[\/pb_glossary] <\/b><span style=\"font-weight: 400\">is a [pb_glossary id=\"2924\"]foliated[\/pb_glossary] [pb_glossary id=\"2684\"]metamorphic rock[\/pb_glossary] in which platy [pb_glossary id=\"2687\"]minerals[\/pb_glossary] have grown larger and the surface of the [pb_glossary id=\"2924\"]foliation[\/pb_glossary] shows a sheen from light reflecting from the grains, perhaps even a wavy appearance, called crenulations<\/span><span style=\"font-weight: 400\">. Similar to [pb_glossary id=\"2928\"]phyllite[\/pb_glossary] but with even larger grains is the [pb_glossary id=\"2924\"]foliated[\/pb_glossary] [pb_glossary id=\"2684\"]metamorphic rock[\/pb_glossary] <\/span><b>[pb_glossary id=\"2929\"]schist[\/pb_glossary]<\/b><span style=\"font-weight: 400\">, which has large platy grains visible as individual crystals. Common [pb_glossary id=\"2687\"]minerals[\/pb_glossary] are [pb_glossary id=\"1914\"]muscovite[\/pb_glossary], [pb_glossary id=\"1914\"]biotite[\/pb_glossary], and porphyroblasts of garnets. A porphyroblast is a large crystal of a particular [pb_glossary id=\"2687\"]mineral[\/pb_glossary] surrounded by small grains. <\/span><b>[pb_glossary id=\"2930\"]Schistosity[\/pb_glossary]<\/b><span style=\"font-weight: 400\"> is a textural description of [pb_glossary id=\"2924\"]foliation[\/pb_glossary] created by the parallel alignment of platy visible grains. Some schists are named for their [pb_glossary id=\"2687\"]minerals[\/pb_glossary] such as [pb_glossary id=\"1914\"]mica[\/pb_glossary] [pb_glossary id=\"2929\"]schist[\/pb_glossary] (mostly micas), garnet [pb_glossary id=\"2929\"]schist[\/pb_glossary] ([pb_glossary id=\"1914\"]mica[\/pb_glossary] [pb_glossary id=\"2929\"]schist[\/pb_glossary] with garnets), and staurolite [pb_glossary id=\"2929\"]schist[\/pb_glossary] ([pb_glossary id=\"1914\"]mica[\/pb_glossary] schists with staurolite).<\/span>\n\n&nbsp;\n\n[caption id=\"attachment_3176\" align=\"aligncenter\" width=\"413\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-Schist_detail-e1492392805920.jpg\"><img class=\"wp-image-442\" title=\"Source: By Michael C. Rygel (Own work) [CC BY-SA 3.0 (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0)], via Wikimedia Commons\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-Schist_detail-e1492392805920-300x184.jpg\" alt=\"Schist is a scalely looking foliated metamorphic rock.\" width=\"413\" height=\"253\"><\/a> Schist[\/caption]\n\n[caption id=\"attachment_3177\" align=\"aligncenter\" width=\"420\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-11-Muscovite-schist.jpg\"><img class=\"wp-image-443\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-11-Muscovite-schist-300x165.jpg\" alt=\"Shiny foliated rock with small crystals of red faceted garnet among the foliated micas.\" width=\"420\" height=\"230\"><\/a> Garnet staurolite muscovite schist. (Source: Peter Davis)[\/caption]\n\n[caption id=\"attachment_3179\" align=\"alignleft\" width=\"354\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2_Gneiss.jpg\">&lt;img class=\"wp-image-3179\" title=\"By No machine-readable author provided. Siim assumed (based on copyright claims). [<a href=\"\/\/www.gnu.org\/copyleft\/fdl.html&quot;\">GFDL<\/a> or <a href=\"\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;\">CC-BY-SA-3.0<\/a>], <a href=\"\/\/commons.wikimedia.org\/wiki\/File%3AGneiss.jpg&quot;\">via Wikimedia Commons<\/a>\" src=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2_Gneiss-300x181.jpg\" alt=\"Alternating bands of light and dark minerals.\" width=\"354\" height=\"213\"&gt;<\/a> Gneiss[\/caption]&nbsp;\n\n<b>[pb_glossary id=\"2931\"]Gneissic banding[\/pb_glossary]&nbsp;<\/b><span style=\"font-weight: 400\">is a [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] [pb_glossary id=\"2924\"]foliation[\/pb_glossary]<\/span> <span style=\"font-weight: 400\">in which visible [pb_glossary id=\"2709\"]silicate[\/pb_glossary] [pb_glossary id=\"2687\"]minerals[\/pb_glossary] separate into dark and light [pb_glossary id=\"2931\"]bands[\/pb_glossary] or lineations. These grains tend to be coarse and often folded. A rock with this [pb_glossary id=\"2919\"]texture[\/pb_glossary] is called <\/span><b>[pb_glossary id=\"2932\"]gneiss[\/pb_glossary]<\/b><span style=\"font-weight: 400\">. Since gneisses form at the highest temperatures and pressures, some [pb_glossary id=\"1177\"]partial melting[\/pb_glossary] may occur. This partially melted rock is a transition between [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] and [pb_glossary id=\"2675\"]igneous[\/pb_glossary] rocks called a <\/span><b>[pb_glossary id=\"2933\"]migmatite[\/pb_glossary]<\/b><b>.<\/b>\n\n[caption id=\"attachment_2482\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/06.2-15-Mt-Blaca-Migmatite-1.jpg\"><img class=\"size-medium wp-image-48\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-15-Mt-Blaca-Migmatite-1-300x225.jpg\" alt=\"Swirling bands of light and dark minerals.\" width=\"300\" height=\"225\"><\/a> Migmatite, a rock which was partially molten. (Source: Peter Davis)[\/caption]\n\n<span style=\"font-weight: 400\">[pb_glossary id=\"2933\"]Migmatites[\/pb_glossary] appear as dark and light [pb_glossary id=\"2931\"]banded[\/pb_glossary] [pb_glossary id=\"2932\"]gneiss[\/pb_glossary] that may be swirled or twisted some since some [pb_glossary id=\"2687\"]minerals[\/pb_glossary] started to melt. Thin accumulations of light colored rock layers can occur in a darker rock that are parallel to each other, or even cut across the [pb_glossary id=\"2932\"]gneissic[\/pb_glossary] [pb_glossary id=\"2924\"]foliation[\/pb_glossary]. The lighter colored layers are interpreted to be the result of the separation of a [pb_glossary id=\"1954\"]felsic[\/pb_glossary] [pb_glossary id=\"2675\"]igneous[\/pb_glossary] melt from the adjacent highly metamorphosed darker layers, or injection of a [pb_glossary id=\"1954\"]felsic[\/pb_glossary] melt from some distance away. <\/span>\n<h3><span style=\"font-weight: 400\">6.2.2 Non-foliated<\/span><\/h3>\n[caption id=\"attachment_3185\" align=\"aligncenter\" width=\"413\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-21-Marble-scaled.jpg\"><img class=\"wp-image-3185\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-21-Marble-scaled-1.jpg\" alt=\"pink crystallized rock with interlocking crystals\" width=\"413\" height=\"300\"><\/a> Marble (Source: Peter Davis)[\/caption]\n\n[caption id=\"attachment_3188\" align=\"aligncenter\" width=\"420\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-20-Baraboo.jpg\"><img class=\"wp-image-445\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-20-Baraboo-300x275.jpg\" alt=\"Crystallized rock with interlocking crystals.\" width=\"420\" height=\"385\"><\/a> Baraboo Quartzite[\/caption]\n\n<b>[pb_glossary id=\"2934\"]Non-foliated[\/pb_glossary]<\/b><span style=\"font-weight: 400\"> textures do not have lineations, foliations, or other alignments of [pb_glossary id=\"2687\"]mineral[\/pb_glossary] grains. [pb_glossary id=\"2934\"]Non-foliated[\/pb_glossary] [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] rocks are typically [pb_glossary id=\"2831\"]composed[\/pb_glossary] of just one [pb_glossary id=\"2687\"]mineral[\/pb_glossary], and therefore, usually show the effects of [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary] with [pb_glossary id=\"2920\"]recrystallization[\/pb_glossary] in which crystals grow together, but with no preferred direction. The two most common examples of [pb_glossary id=\"2934\"]non-foliated[\/pb_glossary] rocks are [pb_glossary id=\"2935\"]quartzite[\/pb_glossary] and [pb_glossary id=\"2936\"]marble[\/pb_glossary]. <\/span><b>[pb_glossary id=\"2935\"]Quartzite[\/pb_glossary] <\/b><span style=\"font-weight: 400\">is a [pb_glossary id=\"2684\"]metamorphic rock[\/pb_glossary] from the [pb_glossary id=\"2688\"]protolith[\/pb_glossary] [pb_glossary id=\"2834\"]sandstone[\/pb_glossary]. In [pb_glossary id=\"2935\"]quartzites[\/pb_glossary], the [pb_glossary id=\"1915\"]quartz[\/pb_glossary] grains from the original [pb_glossary id=\"2834\"]sandstone[\/pb_glossary] are enlarged and interlocked by [pb_glossary id=\"2920\"]recrystallization[\/pb_glossary]. A defining characteristic for distinguishing [pb_glossary id=\"2935\"]quartzite[\/pb_glossary] from [pb_glossary id=\"2834\"]sandstone[\/pb_glossary] is that when broken with a rock hammer, the [pb_glossary id=\"1915\"]quartz[\/pb_glossary] crystals break across the grains. In a [pb_glossary id=\"2834\"]sandstone[\/pb_glossary], only a thin [pb_glossary id=\"2687\"]mineral[\/pb_glossary] cement holds the grains together, meaning that a broken piece of [pb_glossary id=\"2834\"]sandstone[\/pb_glossary] will leave the grains intact. Because most [pb_glossary id=\"2834\"]sandstones[\/pb_glossary] are rich in [pb_glossary id=\"1915\"]quartz[\/pb_glossary], and [pb_glossary id=\"1915\"]quartz[\/pb_glossary] is a mechanically and chemically durable substance, [pb_glossary id=\"2935\"]quartzite[\/pb_glossary] is very hard and resistant to [pb_glossary id=\"2676\"]weathering[\/pb_glossary].<\/span>\n\n<b>[pb_glossary id=\"2936\"]Marble[\/pb_glossary]<\/b><span style=\"font-weight: 400\"> is metamorphosed [pb_glossary id=\"2851\"]limestone[\/pb_glossary] (or dolostone) [pb_glossary id=\"2831\"]composed[\/pb_glossary] of [pb_glossary id=\"1918\"]calcite[\/pb_glossary] (or dolomite). [pb_glossary id=\"2920\"]Recrystallization[\/pb_glossary] typically generates larger interlocking crystals of [pb_glossary id=\"1918\"]calcite[\/pb_glossary] or dolomite. [pb_glossary id=\"2936\"]Marble[\/pb_glossary] and [pb_glossary id=\"2935\"]quartzite[\/pb_glossary] often look similar, but these [pb_glossary id=\"2687\"]minerals[\/pb_glossary] are considerably softer than [pb_glossary id=\"1915\"]quartz[\/pb_glossary]. Another way to distinguish [pb_glossary id=\"2936\"]marble[\/pb_glossary] from [pb_glossary id=\"2935\"]quartzite[\/pb_glossary] is with a drop of dilute hydrochloric acid. [pb_glossary id=\"2936\"]Marble[\/pb_glossary] will effervesce (fizz) if it is made of [pb_glossary id=\"1918\"]calcite[\/pb_glossary].<\/span>\n\n<span style=\"font-weight: 400\">A third [pb_glossary id=\"2934\"]non-foliated[\/pb_glossary] rock is <\/span><b>[pb_glossary id=\"2937\"]hornfels[\/pb_glossary] <\/b><span style=\"font-weight: 400\">identified by its dense, fine grained, hard, blocky or splintery [pb_glossary id=\"2919\"]texture[\/pb_glossary] [pb_glossary id=\"2831\"]composed[\/pb_glossary] of several [pb_glossary id=\"2709\"]silicate[\/pb_glossary] [pb_glossary id=\"2687\"]minerals[\/pb_glossary]. Crystals in [pb_glossary id=\"2937\"]hornfels[\/pb_glossary] grow smaller with [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary], and become so small that specialized study is required to identify them. These are common around [pb_glossary id=\"1939\"]intrusive[\/pb_glossary] [pb_glossary id=\"2675\"]igneous[\/pb_glossary] bodies and<\/span><span style=\"font-weight: 400\">&nbsp;are hard to identify. The [pb_glossary id=\"2688\"]protolith[\/pb_glossary] of [pb_glossary id=\"2937\"]hornfels[\/pb_glossary] can be even harder to distinguish, which can be anything from [pb_glossary id=\"2837\"]mudstone[\/pb_glossary] to [pb_glossary id=\"1961\"]basalt[\/pb_glossary].<\/span>\n\n[caption id=\"attachment_3191\" align=\"aligncenter\" width=\"413\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Sample_of_Quartzite-e1493780752118.jpg\">&lt;img class=\"wp-image-3191\" title=\"By Manishwiki15 (Own work) [<a href=\"\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;\">CC BY-SA 3.0<\/a>], <a href=\"\/\/commons.wikimedia.org\/wiki\/File%3ASample_of_Quartzite.JPG&quot;\">via Wikimedia Commons<\/a>\" src=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Sample_of_Quartzite-e1493780752118-300x210.jpg\" alt=\"Interlocking quartz grains in a quartzite.\" width=\"413\" height=\"289\"&gt;<\/a> Macro view of quartzite. Note the interconnectedness of the grains.[\/caption][caption id=\"attachment_3192\" align=\"aligncenter\" width=\"420\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/640px-CoralPinkSandDunesSand.jpg\">&lt;img class=\"wp-image-3192\" title=\"By Wilson44691 (Own work) [Public domain], <a href=\"\/\/commons.wikimedia.org\/wiki\/File%3ACoralPinkSandDunesSand.JPG&quot;\">via Wikimedia Commons<\/a>\" src=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/640px-CoralPinkSandDunesSand-300x225.jpg\" alt=\"Undeformed quartz grains do not interlock.\" width=\"420\" height=\"315\"&gt;<\/a> Unmetamorphosed, unconsolidated sand grains have space between the grains.[\/caption]\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"38\"]\n\n[caption id=\"attachment_4001\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/6.2-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-446\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/6.2-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 6.2 via this QR Code.[\/caption]\n<h2><span style=\"font-weight: 400\">6.3 Metamorphic Grade<\/span><\/h2>\n[caption id=\"attachment_3194\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.4_Garnet_Mica_Schist_Syros_Greece.jpg\"><img class=\"wp-image-447 size-medium\" title=\"By Graeme Churchard (GOC53) http:\/\/www.flickr.com\/people\/graeme\/ [CC BY 2.0 (http:\/\/creativecommons.org\/licenses\/by\/2.0)], via Wikimedia Commons\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_Garnet_Mica_Schist_Syros_Greece-300x225.jpg\" alt=\"Large weathered garnet crystals in a matrix of platy micas. The garnets are round-shaped with octagonal sides.\" width=\"300\" height=\"225\"><\/a> Garnet schist.[\/caption][pb_glossary id=\"2914\"]Metamorphic[\/pb_glossary] [pb_glossary id=\"2938\"]grade[\/pb_glossary] refers to the range of [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] change a rock undergoes, progressing from low (little [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] change) [pb_glossary id=\"2938\"]grade[\/pb_glossary] to high (significant metamorphic change) grade. Low-[pb_glossary id=\"2938\"]grade[\/pb_glossary] [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary] begins at temperatures and pressures just above [pb_glossary id=\"2683\"]sedimentary rock[\/pb_glossary] conditions. The sequence [pb_glossary id=\"2926\"]slate[\/pb_glossary]\u2192[pb_glossary id=\"2928\"]phyllite[\/pb_glossary]\u2192[pb_glossary id=\"2929\"]schist[\/pb_glossary]\u2192[pb_glossary id=\"2932\"]gneiss[\/pb_glossary] illustrates an increasing [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] [pb_glossary id=\"2938\"]grade[\/pb_glossary].\n\nGeologists use <strong>[pb_glossary id=\"2939\"]index minerals[\/pb_glossary]<\/strong> that form at certain temperatures and pressures to identify [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] [pb_glossary id=\"2938\"]grade[\/pb_glossary]. These [pb_glossary id=\"2939\"]index minerals[\/pb_glossary] also provide important clues to a rock\u2019s sedimentary [pb_glossary id=\"2688\"]protolith[\/pb_glossary] and the [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] conditions that created it. Chlorite, [pb_glossary id=\"1914\"]muscovite[\/pb_glossary], [pb_glossary id=\"1914\"]biotite[\/pb_glossary], garnet, and staurolite are [pb_glossary id=\"2939\"]index minerals[\/pb_glossary] representing a respective sequence of low-to-high [pb_glossary id=\"2938\"]grade[\/pb_glossary] rock. The figure shows a <strong>[pb_glossary id=\"2941\"]phase diagram[\/pb_glossary]<\/strong> of three [pb_glossary id=\"2939\"]index minerals[\/pb_glossary]\u2014sillimanite, kyanite, and andalusite\u2014with the same chemical formula (Al<sub>2<\/sub>SiO<sub>5<\/sub>) but having different crystal structures (<strong>[pb_glossary id=\"2940\"]polymorphism[\/pb_glossary]<\/strong>) created by different pressure and [pb_glossary id=\"2689\"]temperature[\/pb_glossary] conditions.\n\n[h5p id=\"39\"]\n\n[caption id=\"attachment_4003\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/6.3-Phase-diagram-QR-Code.png\"><img class=\"size-thumbnail wp-image-448\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Phase-diagram-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this interactive activity via this QR Code.[\/caption]\n\nSome [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] rocks are named based on the highest [pb_glossary id=\"2938\"]grade[\/pb_glossary] of [pb_glossary id=\"2939\"]index mineral[\/pb_glossary] present. Chlorite [pb_glossary id=\"2929\"]schist[\/pb_glossary] includes the low-[pb_glossary id=\"2938\"]grade[\/pb_glossary] [pb_glossary id=\"2939\"]index mineral[\/pb_glossary] chlorite. [pb_glossary id=\"1914\"]Muscovite[\/pb_glossary] [pb_glossary id=\"2929\"]schist[\/pb_glossary] contains the slightly higher [pb_glossary id=\"2938\"]grade[\/pb_glossary] [pb_glossary id=\"1914\"]muscovite[\/pb_glossary], indicating a greater degree of [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary]. Garnet [pb_glossary id=\"2929\"]schist[\/pb_glossary] includes the high [pb_glossary id=\"2938\"]grade[\/pb_glossary] [pb_glossary id=\"2939\"]index mineral[\/pb_glossary] garnet, and indicating it has experienced much higher pressures and temperatures than chlorite.\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"40\"]\n\n[caption id=\"attachment_4002\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/6.3-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-449\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 6.3 via this QR Code.[\/caption]\n<h2><span style=\"font-weight: 400\">6.4 Metamorphic Environments<\/span><\/h2>\n<span style=\"font-weight: 400\">As with [pb_glossary id=\"2675\"]igneous[\/pb_glossary] processes, [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] rocks form at different zones of pressure (depth) and [pb_glossary id=\"2689\"]temperature[\/pb_glossary] as shown on the pressure-[pb_glossary id=\"2689\"]temperature[\/pb_glossary] (P-T) diagram. The term <\/span><b>[pb_glossary id=\"2913\"]facies[\/pb_glossary] <\/b><span style=\"font-weight: 400\">is an [pb_glossary id=\"2644\"]objective[\/pb_glossary] description of a rock. In [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] rocks [pb_glossary id=\"2913\"]facies[\/pb_glossary]&nbsp;are groups of [pb_glossary id=\"2687\"]minerals[\/pb_glossary] called [pb_glossary id=\"2687\"]mineral[\/pb_glossary] assemblages. The names of <\/span><b>[pb_glossary id=\"2942\"]metamorphic facies[\/pb_glossary]<\/b><span style=\"font-weight: 400\"> on the pressure-[pb_glossary id=\"2689\"]temperature[\/pb_glossary] diagram reflect [pb_glossary id=\"2687\"]minerals[\/pb_glossary] and [pb_glossary id=\"2687\"]mineral[\/pb_glossary] assemblages that are stable at these pressures and temperatures and provide information about the [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] processes that have affected the rocks. This is useful when interpreting the history of a [pb_glossary id=\"2684\"]metamorphic rock[\/pb_glossary].<\/span>\n\n[caption id=\"attachment_3196\" align=\"aligncenter\" width=\"1024\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Fig-6.24-PT-graph.png\"><img class=\"wp-image-450 size-large\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig-6.24-PT-graph-1024x683.png\" alt=\"\" width=\"1024\" height=\"683\"><\/a> Pressure-temperature graphs of various metamorphic facies. (Source: Peter Davis)[\/caption]\n\n<span style=\"font-weight: 400\">In the late 1800s, British geologist George Barrow mapped zones of [pb_glossary id=\"2687\"]index minerals[\/pb_glossary] in different [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] zones of an area that underwent [pb_glossary id=\"2946\"]regional metamorphism[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. Barrow outlined a progression of [pb_glossary id=\"2939\"]index minerals[\/pb_glossary], named the Barrovian Sequence, that represents increasing [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] [pb_glossary id=\"2938\"]grade[\/pb_glossary]: chlorite (slates and phyllites) -&gt; [pb_glossary id=\"1914\"]biotite[\/pb_glossary] (phyllites and schists) -&gt; garnet (schists) -&gt; staurolite (schists) -&gt; kyanite (schists) -&gt; sillimanite (schists and gneisses).<\/span>\n\n[caption id=\"attachment_3199\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/1024px-Scotland_metamorphic_zones_EN.svg_.png\"><img class=\"size-medium wp-image-451\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/1024px-Scotland_metamorphic_zones_EN.svg_-300x208.png\" alt=\"Metamorphic zones in Scotland show increasing metamorphic grade across a transect of a deformed mountain range.\" width=\"300\" height=\"208\"><\/a> Barrovian sequence in Scotland.[\/caption]\n\n<span style=\"font-weight: 400\">The first of the Barrovian sequence has a [pb_glossary id=\"2687\"]mineral[\/pb_glossary] group that is commonly found in the [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] greenschist [pb_glossary id=\"2913\"]facies[\/pb_glossary]. Greenschist rocks form under relatively low pressure and temperatures and represent the fringes of [pb_glossary id=\"2946\"]regional metamorphism[\/pb_glossary]. The \u201cgreen\u201d part of the name is derived from &nbsp;green [pb_glossary id=\"2687\"]minerals[\/pb_glossary] like chlorite, serpentine, and epidote, and the \u201c[pb_glossary id=\"2929\"]schist[\/pb_glossary]\u201d part is applied due to the presence of platy [pb_glossary id=\"2687\"]minerals[\/pb_glossary] such as [pb_glossary id=\"1914\"]muscovite[\/pb_glossary].<\/span>\n\n<span style=\"font-weight: 400\">Many different styles of [pb_glossary id=\"2942\"]metamorphic facies[\/pb_glossary] are recognized, tied to different geologic and [pb_glossary id=\"2576\"]tectonic[\/pb_glossary] processes. Recognizing these [pb_glossary id=\"2913\"]facies[\/pb_glossary] is the most direct way to interpret the [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] history of a rock. A simplified list of major [pb_glossary id=\"2942\"]metamorphic facies[\/pb_glossary] is given below.<\/span>\n<h3><span style=\"font-weight: 400\">6.4.1 Burial Metamorphism<\/span><\/h3>\n<b>[pb_glossary id=\"2943\"]Burial metamorphism[\/pb_glossary]<\/b><span style=\"font-weight: 400\"> occurs when rocks are deeply buried, at depths of more than 2000 meters (1.24 miles)<\/span><span style=\"font-weight: 400\">. [pb_glossary id=\"2943\"]Burial metamorphism[\/pb_glossary] commonly occurs in [pb_glossary id=\"1463\"]sedimentary basins[\/pb_glossary], where rocks are buried deeply by overlying [pb_glossary id=\"2678\"]sediments[\/pb_glossary]. As an [pb_glossary id=\"1445\"]extension[\/pb_glossary] of [pb_glossary id=\"2827\"]diagenesis[\/pb_glossary], a process that occurs during [pb_glossary id=\"2682\"]lithification[\/pb_glossary] (<a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/5-weathering-erosion-and-sedimentary-rocks\/\">Chapter 5<\/a>), [pb_glossary id=\"2943\"]burial metamorphism[\/pb_glossary] can cause clay [pb_glossary id=\"2687\"]minerals[\/pb_glossary], such as smectite, in [pb_glossary id=\"2839\"]shales[\/pb_glossary] to change to another clay [pb_glossary id=\"2687\"]mineral[\/pb_glossary] illite. Or it can cause [pb_glossary id=\"1915\"]quartz[\/pb_glossary] [pb_glossary id=\"2834\"]sandstone[\/pb_glossary] to metamorphose into the [pb_glossary id=\"2935\"]quartzite[\/pb_glossary] such the Big Cottonwood [pb_glossary id=\"2960\"]Formation[\/pb_glossary] in the Wasatch Range of Utah. This [pb_glossary id=\"2960\"]formation[\/pb_glossary] was deposited as ancient near-[pb_glossary id=\"3195\"]shore[\/pb_glossary] sands in the late [pb_glossary id=\"2209\"]Proterozoic[\/pb_glossary] (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/7-geologic-time\/\">Chapter 7<\/a>), deeply buried and metamorphosed to [pb_glossary id=\"2935\"]quartzite[\/pb_glossary], folded, and later exposed at the surface in the Wasatch Range today. Increase of [pb_glossary id=\"2689\"]temperature[\/pb_glossary] with depth in combination with an increase of [pb_glossary id=\"2917\"]confining[\/pb_glossary] pressure produces low-[pb_glossary id=\"2938\"]grade[\/pb_glossary] [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] rocks with a [pb_glossary id=\"2687\"]mineral[\/pb_glossary] assemblages indicative of a zeolite [pb_glossary id=\"2913\"]facies[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. <\/span>\n<h3><span style=\"font-weight: 400\">6.4.2 Contact Metamorphism<\/span><\/h3>\n<strong>[pb_glossary id=\"2944\"]Contact metamorphism[\/pb_glossary]<\/strong> occurs in rock exposed to high [pb_glossary id=\"2689\"]temperature[\/pb_glossary] and low pressure, as might happen when hot [pb_glossary id=\"2672\"]magma[\/pb_glossary] intrudes into or [pb_glossary id=\"2673\"]lava[\/pb_glossary] flows over pre-existing [pb_glossary id=\"2688\"]protolith[\/pb_glossary]. This combination of high [pb_glossary id=\"2689\"]temperature[\/pb_glossary] and low pressure produces numerous [pb_glossary id=\"2942\"]metamorphic facies[\/pb_glossary]. The lowest pressure conditions produce [pb_glossary id=\"2937\"]hornfels[\/pb_glossary] [pb_glossary id=\"2913\"]facies[\/pb_glossary], while higher pressure creates greenschist, amphibolite, or granulite [pb_glossary id=\"2913\"]facies[\/pb_glossary].\n\nAs with all [pb_glossary id=\"2684\"]metamorphic rock[\/pb_glossary], the [pb_glossary id=\"2688\"]parent rock[\/pb_glossary] [pb_glossary id=\"2919\"]texture[\/pb_glossary] and chemistry are major factors in determining the final outcome of the [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] process, including what [pb_glossary id=\"2939\"]index minerals[\/pb_glossary] are present. Fine-grained [pb_glossary id=\"2839\"]shale[\/pb_glossary] and [pb_glossary id=\"1961\"]basalt[\/pb_glossary], which happen to be chemically similar, characteristically recrystallize to produce [pb_glossary id=\"2937\"]hornfels[\/pb_glossary]. [pb_glossary id=\"2834\"]Sandstone[\/pb_glossary] (silica) surrounding an [pb_glossary id=\"2675\"]igneous[\/pb_glossary] intrusion becomes [pb_glossary id=\"2935\"]quartzite[\/pb_glossary] via [pb_glossary id=\"2944\"]contact metamorphism[\/pb_glossary], and [pb_glossary id=\"2851\"]limestone[\/pb_glossary] ([pb_glossary id=\"1917\"]carbonate[\/pb_glossary]) becomes [pb_glossary id=\"2936\"]marble[\/pb_glossary].\n\n[caption id=\"attachment_3201\" align=\"alignleft\" width=\"185\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Metamorphic_Aureole_in_the_Henry_Mountains.jpg\">&lt;img class=\"wp-image-3201\" title=\"By Random Tree (Own work) [<a href=\"\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en&quot;\">CC0<\/a>], <a href=\"\/\/commons.wikimedia.org\/wiki\/File%3AMetamorphic_Aureole_in_the_Henry_Mountains.JPG&quot;\">via Wikimedia Commons<\/a>\" src=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Metamorphic_Aureole_in_the_Henry_Mountains-300x225.jpg\" alt=\"Altered rock adjacent to an igneous intrusion.\" width=\"185\" height=\"139\"&gt;<\/a> Contact metamorphism in outcrop.[\/caption]When [pb_glossary id=\"2944\"]contact metamorphism[\/pb_glossary] occurs deeper in the Earth, [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary] can be seen as rings of [pb_glossary id=\"2913\"]facies[\/pb_glossary] around the intrusion, resulting in <strong>[pb_glossary id=\"2945\"]aureoles[\/pb_glossary]<\/strong>. These differences in [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary] appear as distinct [pb_glossary id=\"2931\"]bands[\/pb_glossary] surrounding the intrusion, as can be seen around the Alta Stock in Little Cottonwood Canyon, Utah. The Alta Stock is a [pb_glossary id=\"1962\"]granite[\/pb_glossary] intrusion surrounded first by rings of the [pb_glossary id=\"2939\"]index minerals[\/pb_glossary] [pb_glossary id=\"2713\"]amphibole[\/pb_glossary] (tremolite) and [pb_glossary id=\"2711\"]olivine[\/pb_glossary] (forsterite), with a ring of talc (dolostone) located further away<span style=\"font-weight: 400\">.<\/span>\n<h3><span style=\"font-weight: 400\">6.4.3 Regional Metamorphism<\/span><\/h3>\n<strong>[pb_glossary id=\"2946\"]Regional metamorphism[\/pb_glossary]<\/strong> occurs when [pb_glossary id=\"2688\"]parent rock[\/pb_glossary] is subjected to increased [pb_glossary id=\"2689\"]temperature[\/pb_glossary] and pressure over a large area, and is often located in mountain ranges created by converging [pb_glossary id=\"2575\"]continental[\/pb_glossary] crustal [pb_glossary id=\"2591\"]plates[\/pb_glossary]. This is the setting for the Barrovian sequence of rock [pb_glossary id=\"2913\"]facies[\/pb_glossary], with the lowest [pb_glossary id=\"2938\"]grade[\/pb_glossary] of [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary] occurring on the flanks of the mountains and highest [pb_glossary id=\"2938\"]grade[\/pb_glossary] near the [pb_glossary id=\"2589\"]core[\/pb_glossary] of the mountain range, closest to the [pb_glossary id=\"2600\"]convergent[\/pb_glossary] boundary.\n\nAn example of an old regional [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] environment is visible in the northern Appalachian Mountains while driving east from New York state through Vermont and into New Hampshire. Along this route the degree of [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary] gradually increases from sedimentary [pb_glossary id=\"2688\"]parent rock[\/pb_glossary], to low-[pb_glossary id=\"2938\"]grade[\/pb_glossary] [pb_glossary id=\"2684\"]metamorphic rock[\/pb_glossary], then higher-[pb_glossary id=\"2938\"]grade[\/pb_glossary] [pb_glossary id=\"2684\"]metamorphic rock[\/pb_glossary], and eventually the [pb_glossary id=\"2675\"]igneous[\/pb_glossary] [pb_glossary id=\"2589\"]core[\/pb_glossary]. The rock sequence is [pb_glossary id=\"2683\"]sedimentary rock[\/pb_glossary], [pb_glossary id=\"2926\"]slate[\/pb_glossary], [pb_glossary id=\"2928\"]phyllite[\/pb_glossary], [pb_glossary id=\"2929\"]schist[\/pb_glossary], [pb_glossary id=\"2932\"]gneiss[\/pb_glossary], [pb_glossary id=\"2933\"]migmatite[\/pb_glossary], and [pb_glossary id=\"1962\"]granite[\/pb_glossary]. In fact, New Hampshire is nicknamed the [pb_glossary id=\"1962\"]Granite[\/pb_glossary] State. The reverse sequence can be seen heading east, from eastern New Hampshire to the [pb_glossary id=\"2890\"]coast[\/pb_glossary]<span style=\"font-weight: 400\">.<\/span>\n<h3><span style=\"font-weight: 400\">6.4.4 Subduction Zone Metamorphism<\/span><\/h3>\n[caption id=\"attachment_3204\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.4-25-Blueschist-e1492235808840-scaled.jpg\"><img class=\"wp-image-3204 size-medium\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4-25-Blueschist-e1492235808840-scaled-1.jpg\" alt=\"A blue rock with bands of silvery mica grains.\" width=\"300\" height=\"225\"><\/a> Blueschist (Source: Peter Davis)[\/caption]\n\n[pb_glossary id=\"2947\"]Subduction zone[\/pb_glossary] metamorphism is a type of [pb_glossary id=\"2946\"]regional metamorphism[\/pb_glossary] that occurs when a [pb_glossary id=\"2605\"]slab[\/pb_glossary] of [pb_glossary id=\"2581\"]oceanic crust[\/pb_glossary] is [pb_glossary id=\"2602\"]subducted[\/pb_glossary] under [pb_glossary id=\"2575\"]continental crust[\/pb_glossary] (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/2-plate-tectonics\/\">Chapter 2<\/a>). Because rock is a good insulator, the [pb_glossary id=\"2689\"]temperature[\/pb_glossary] of the descending [pb_glossary id=\"2581\"]oceanic[\/pb_glossary] [pb_glossary id=\"2605\"]slab[\/pb_glossary] increases slowly relative to the more rapidly increasing pressure, creating a [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] environment of high pressure and low [pb_glossary id=\"2689\"]temperature[\/pb_glossary]. Glaucophane, which has a distinctive blue color, is an [pb_glossary id=\"2939\"]index mineral[\/pb_glossary] found in [pb_glossary id=\"2948\"]blueschist[\/pb_glossary] [pb_glossary id=\"2913\"]facies[\/pb_glossary] (see [pb_glossary id=\"2942\"]metamorphic facies[\/pb_glossary] diagram). The California [pb_glossary id=\"2890\"]Coast[\/pb_glossary] Range near San Francisco has [pb_glossary id=\"2948\"]blueschist[\/pb_glossary]-[pb_glossary id=\"2913\"]facies[\/pb_glossary] rocks created by [pb_glossary id=\"2602\"]subduction[\/pb_glossary]-zone [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary], which include rocks made of [pb_glossary id=\"2948\"]blueschist[\/pb_glossary], greenstone, and red [pb_glossary id=\"2849\"]chert[\/pb_glossary]. Greenstone, which is metamorphized [pb_glossary id=\"1961\"]basalt[\/pb_glossary], gets its color from the [pb_glossary id=\"2939\"]index mineral[\/pb_glossary] chlorite.\n<h3><span style=\"font-weight: 400\">6.4.5 Fault Metamorphism<\/span><\/h3>\n[caption id=\"attachment_3208\" align=\"alignright\" width=\"398\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.4-28-Mylonite.jpg\"><img class=\"wp-image-453\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4-28-Mylonite-300x116.jpg\" alt=\"Layers of shears material with rotated grains.\" width=\"398\" height=\"153\"><\/a> Mylonite (Source: Peter Davis)[\/caption]\n\n<span style=\"font-weight: 400\">There are a range of [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] rocks made along [pb_glossary id=\"3065\"]faults[\/pb_glossary]. Near the surface, rocks are involved in repeated [pb_glossary id=\"2583\"]brittle[\/pb_glossary] [pb_glossary id=\"3065\"]faulting[\/pb_glossary] produce a material called <\/span><i><span style=\"font-weight: 400\">rock flour,<\/span><\/i><span style=\"font-weight: 400\"> which is rock ground up to the particle size of flour used for food.<\/span> <span style=\"font-weight: 400\">At lower depths,<\/span> <span style=\"font-weight: 400\">[pb_glossary id=\"3065\"]faulting[\/pb_glossary] create <\/span><b>cataclastites<\/b><span style=\"font-weight: 400\">, chaotically-crushed mixes of rock material with little internal [pb_glossary id=\"2919\"]texture[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. At depths below [pb_glossary id=\"2949\"]cataclasites[\/pb_glossary], where [pb_glossary id=\"2916\"]strain[\/pb_glossary] becomes [pb_glossary id=\"2582\"]ductile[\/pb_glossary], [pb_glossary id=\"2950\"]mylonites[\/pb_glossary] are formed. <\/span><b>[pb_glossary id=\"2950\"]Mylonites[\/pb_glossary]<\/b> <span style=\"font-weight: 400\">are [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] rocks created by dynamic [pb_glossary id=\"2920\"]recrystallization[\/pb_glossary] through directed [pb_glossary id=\"3112\"]shear forces[\/pb_glossary], generally resulting in a reduction of [pb_glossary id=\"2828\"]grain size[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. When larger, stronger crystals (like [pb_glossary id=\"1916\"]feldspar[\/pb_glossary], [pb_glossary id=\"1915\"]quartz[\/pb_glossary], garnet) embedded in a [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] matrix are [pb_glossary id=\"1447\"]sheared[\/pb_glossary] into an asymmetrical eye-shaped crystal, an <\/span><b>[pb_glossary id=\"2951\"]augen[\/pb_glossary] <\/b><span style=\"font-weight: 400\">is formed<\/span><span style=\"font-weight: 400\">.<\/span>\n\n[caption id=\"attachment_3211\" align=\"aligncenter\" width=\"540\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.4-29-Augen.jpg\"><img class=\"wp-image-454\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4-29-Augen.jpg\" alt=\"Rounded mineral grains from shear forces.\" width=\"540\" height=\"221\"><\/a> Examples of augens. (Source: Peter Davis)[\/caption]\n<h3><span style=\"font-weight: 400\">6.4.6 Shock Metamorphism<\/span><\/h3>\n[caption id=\"attachment_3212\" align=\"alignright\" width=\"218\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/820qtz.jpg\">&lt;img class=\"wp-image-3212\" title=\"By Glen A. Izett [Public domain], <a href=\"\/\/commons.wikimedia.org\/wiki\/File%3A820qtz.jpg&quot;\">via Wikimedia Commons<\/a>\" src=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/820qtz-300x253.jpg\" alt=\"A small grain of sand showing a prismatic inside with lines across it.\" width=\"218\" height=\"184\"&gt;<\/a> Shock lamellae in a quartz grain.[\/caption]&nbsp;\n\n<b>Shock<\/b><span style=\"font-weight: 400\"> (also known as impact) <\/span><b>[pb_glossary id=\"2914\"]metamorphism[\/pb_glossary]<\/b><span style=\"font-weight: 400\"> is [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary] resulting from [pb_glossary id=\"2202\"]meteor[\/pb_glossary] or other [pb_glossary id=\"1435\"]bolide[\/pb_glossary] impacts, or from a similar high-pressure shock event. [pb_glossary id=\"2952\"]Shock metamorphism[\/pb_glossary] is the result of very high pressures (and higher, but less extreme temperatures) delivered relatively rapidly. [pb_glossary id=\"2952\"]Shock metamorphism[\/pb_glossary] produces planar [pb_glossary id=\"1448\"]deformation[\/pb_glossary] features, tektites, shatter cones, and [pb_glossary id=\"1915\"]quartz[\/pb_glossary] [pb_glossary id=\"2940\"]polymorphs[\/pb_glossary]. <\/span><span style=\"font-weight: 400\">[pb_glossary id=\"2952\"]Shock metamorphism[\/pb_glossary] produces planar [pb_glossary id=\"1448\"]deformation[\/pb_glossary] features (shock [pb_glossary id=\"2860\"]laminae[\/pb_glossary]), which are narrow planes of glassy material with distinct orientations found in [pb_glossary id=\"2709\"]silicate[\/pb_glossary] [pb_glossary id=\"2687\"]mineral[\/pb_glossary] grains. Shocked [pb_glossary id=\"1915\"]quartz[\/pb_glossary] has planar [pb_glossary id=\"1448\"]deformation[\/pb_glossary] features<\/span><span style=\"font-weight: 400\">.&nbsp;<\/span>\n\n[caption id=\"attachment_3213\" align=\"alignleft\" width=\"187\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.4_ShatterConeCharlevoix1.jpg\"><img class=\"wp-image-455\" title=\"By JMGastonguay (Own work) [CC BY-SA 4.0 (http:\/\/creativecommons.org\/licenses\/by-sa\/4.0)], via Wikimedia Commons\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_ShatterConeCharlevoix1-300x225.jpg\" alt=\"Shatter cones are cone-shaped features, that show lines that converge to cone shapes.\" width=\"187\" height=\"140\"><\/a> Shatter cone.[\/caption]<span style=\"font-weight: 400\">Shatter cones are cone-shaped pieces of rock <\/span><span style=\"font-weight: 400\">created by dynamic branching [pb_glossary id=\"1934\"]fractures[\/pb_glossary] caused by impacts<\/span><span style=\"font-weight: 400\">. While not strictly a [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] structure, they are common around [pb_glossary id=\"2952\"]shock metamorphism[\/pb_glossary]. Their diameter can range from microscopic to several meters. Fine-grained rocks with shatter cones show a distinctive horsetail pattern. <\/span>\n\n<span style=\"font-weight: 400\">[pb_glossary id=\"2952\"]Shock metamorphism[\/pb_glossary] can also produce [pb_glossary id=\"2939\"]index minerals[\/pb_glossary], though they are typically only found via microscopic analysis. The [pb_glossary id=\"1915\"]quartz[\/pb_glossary] [pb_glossary id=\"3362\"]polymorphs[\/pb_glossary] coesite and stishovite are indicative of [pb_glossary id=\"2952\"]impact metamorphism[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. As discussed in chapter 3, [pb_glossary id=\"2940\"]polymorphs[\/pb_glossary] are [pb_glossary id=\"2687\"]minerals[\/pb_glossary] with the same [pb_glossary id=\"2831\"]composition[\/pb_glossary] but different crystal structures. Intense pressure (&gt; 10 GPa) and moderate to high temperatures (700-1200 \u00b0C) are required to form these [pb_glossary id=\"2687\"]minerals[\/pb_glossary].<\/span>\n\n[caption id=\"attachment_3214\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.4_Two_tektites.jpg\"><img class=\"wp-image-456 size-medium\" title=\"By JMGastonguay (Own work) [CC BY-SA 4.0 (http:\/\/creativecommons.org\/licenses\/by-sa\/4.0)], via Wikimedia Commons\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_Two_tektites-300x200.jpg\" alt=\"Shatter cones are cone-shaped features, that show lines that converge to cone shapes.\" width=\"300\" height=\"200\"><\/a> Tektites[\/caption]<span style=\"font-weight: 400\">[pb_glossary id=\"2952\"]Shock metamorphism[\/pb_glossary] can also produce glass. <strong>Tektites<\/strong> are gravel-size glass grains ejected during an impact event<\/span><span style=\"font-weight: 400\">. They resemble [pb_glossary id=\"1181\"]volcanic[\/pb_glossary] glass but, unlike [pb_glossary id=\"1181\"]volcanic[\/pb_glossary] glass, tektites contain no water or [pb_glossary id=\"1943\"]phenocrysts[\/pb_glossary], and have a different bulk and isotopic chemistry. Tektites contain partially melted [pb_glossary id=\"2958\"]inclusions[\/pb_glossary] of shocked [pb_glossary id=\"2687\"]mineral[\/pb_glossary] grains<\/span><span style=\"font-weight: 400\">. Although all are melt glasses, tektites are also chemically distinct from trinitite, which is produced from thermonuclear detonations<\/span><span style=\"font-weight: 400\">, and fulgurites, which are produced by lightning strikes<\/span><span style=\"font-weight: 400\">. All geologic glasses not derived from [pb_glossary id=\"1181\"]volcanoes[\/pb_glossary] can be called with the general term pseudotachylytes<\/span><span style=\"font-weight: 400\">, a name which can also be applied to glasses created by [pb_glossary id=\"3065\"]faulting[\/pb_glossary]. The term pseudo in this context means \u2018false\u2019 or \u2018in the appearance of\u2019, a [pb_glossary id=\"1938\"]volcanic rock[\/pb_glossary] called tachylite because the material observed looks like a [pb_glossary id=\"1938\"]volcanic rock[\/pb_glossary],&nbsp;but is produced by significant [pb_glossary id=\"1447\"]shear[\/pb_glossary] heating. <\/span>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"41\"]\n\n[caption id=\"attachment_4128\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/6.4-Did-I-Get-It-QR-Code.png\"><img class=\"wp-image-457 size-thumbnail\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/6.4-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 6.4 via this QR Code.[\/caption]\n\n<div>\n\n[caption id=\"attachment_4005\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/Metamorphic-Rocks-toast-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-458\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Metamorphic-Rocks-toast-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/Ncr-46YX-N0[\/embed]\n\n<\/div>\nhttps:\/\/youtu.be\/HUydPhIaQQU\n\n[caption id=\"attachment_4004\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/Identifying-Metamorphic-Rock-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-459\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Identifying-Metamorphic-Rock-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n<h2><span style=\"font-weight: 400\">Summary<\/span><\/h2>\n[pb_glossary id=\"2914\"]Metamorphism[\/pb_glossary] is the process that changes existing rocks (called [pb_glossary id=\"2688\"]protoliths[\/pb_glossary]) into new rocks with new [pb_glossary id=\"2687\"]minerals[\/pb_glossary] and new textures. Increases in [pb_glossary id=\"2689\"]temperature[\/pb_glossary] and pressure are the main causes of [pb_glossary id=\"2687\"]metamorphism[\/pb_glossary], with fluids adding important mobilization of materials. The primary way [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] rocks are identified is with [pb_glossary id=\"2919\"]texture[\/pb_glossary]. [pb_glossary id=\"2924\"]Foliated[\/pb_glossary] textures come from platy [pb_glossary id=\"2687\"]minerals[\/pb_glossary] forming planes in a rock, while [pb_glossary id=\"2934\"]non-foliated[\/pb_glossary] [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] rocks have no internal fabric. [pb_glossary id=\"2938\"]Grade[\/pb_glossary] describes the amount of [pb_glossary id=\"2915\"]metamorphism[\/pb_glossary] in a rock, and [pb_glossary id=\"2913\"]facies[\/pb_glossary] are a set of [pb_glossary id=\"2687\"]minerals[\/pb_glossary] that can help guide an observer to an interpretation of the [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] history of a rock. Different [pb_glossary id=\"2576\"]tectonic[\/pb_glossary] or geologic environments cause [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary], including collisions, [pb_glossary id=\"2602\"]subduction[\/pb_glossary], [pb_glossary id=\"3065\"]faulting[\/pb_glossary], and even impacts from space.\n<h3>Take this quiz to check your comprehension of this Chapter.<\/h3>\n[h5p id=\"42\"]\n\n[caption id=\"attachment_4080\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/Ch.6-Review-QR-Code.png\"><img class=\"wp-image-460 size-thumbnail\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.6-Review-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the review quiz for Chapter 6 via this QR Code.[\/caption]\n<h2><span style=\"font-weight: 400\">References<\/span><\/h2>\n<div class=\"csl-bib-body\">\n<ol>\n \t<li class=\"csl-entry\">Bucher, K., and Grapes, R., 2011, Petrogenesis of [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] rocks: Springer, 341 p.<\/li>\n \t<li class=\"csl-entry\">Jeong, I.-K., Heffner, R.H., Graf, M.J., and Billinge, S.J.L., 2003, Lattice dynamics and correlated atomic motion from the atomic pair distribution function: Phys. Rev. B Condens. Matter, v. 67, no. 10, p. 104301.<\/li>\n \t<li class=\"csl-entry\">Marshak, S., 2009, Essentials of Geology, 3rd or 4th Edition:<\/li>\n \t<li class=\"csl-entry\">Proctor, B.P., McAleer, R., Kunk, M.J., and Wintsch, R.P., 2013, Post-Taconic tilting and Acadian structural overprint of the classic Barrovian [pb_glossary id=\"2914\"]metamorphic[\/pb_glossary] [pb_glossary id=\"3135\"]gradient[\/pb_glossary] in Dutchess County, New York: Am. J. Sci., v. 313, no. 7, p. 649\u2013682.<\/li>\n \t<li class=\"csl-entry\">Timeline of Art History, 2007, Reference Reviews, v. 21, no. 8, p. 45\u201345.<\/li>\n<\/ol>\n<\/div>\n<span style=\"font-weight: 400\">&nbsp;<\/span>\n\n&nbsp;","rendered":"<figure id=\"attachment_3142\" aria-describedby=\"caption-attachment-3142\" style=\"width: 1024px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/BCG3-scaled.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-3142 size-large\" title=\"By Matt Affolter\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2021\/12\/BCG3-scaled-1.jpg\" alt=\"The painted wall is a large cliff\" width=\"1024\" height=\"768\" \/><\/a><figcaption id=\"caption-attachment-3142\" class=\"wp-caption-text\">Painted Wall of Black Canyon of the Gunnison National Park, Colorado, made of 1.7 billion-year old gneiss intruded by younger pegmatites.<\/figcaption><\/figure>\n<h1>6 Metamorphic Rocks<\/h1>\n<p><em>Contributing Author: Dr. Peter Davis, Pacific Lutheran University<\/em><\/p>\n<p><b>KEY CONCEPTS<\/b><\/p>\n<ul>\n<li>Describe the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2689\">temperature<\/a> and pressure conditions of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> environment<\/li>\n<li>Identify and describe the three principal <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> agents<\/li>\n<li>Describe what <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2920\">recrystallization<\/a> is and how it affects <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> crystals<\/li>\n<li>Explain what <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2924\">foliation<\/a> is and how it results from directed pressure and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2920\">recrystallization<\/a><\/li>\n<li>Explain the relationships among <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2926\">slate<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2928\">phyllite<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2929\">schist<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2932\">gneiss<\/a> in terms of metamorphic grade<\/li>\n<li>Define <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2939\">index mineral<\/a><\/li>\n<li>Explain how <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2942\">metamorphic facies<\/a> relate to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2591\">plate<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2576\">tectonic<\/a> processes<\/li>\n<li>Describe what a contact <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2945\">aureole<\/a> is and how <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2944\">contact metamorphism<\/a> affects surrounding rock<\/li>\n<li>Describe the role of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2921\">hydrothermal<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a> in forming <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> deposits and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_3325\">ore<\/a> bodies<\/li>\n<\/ul>\n<figure id=\"attachment_2480\" aria-describedby=\"caption-attachment-2480\" style=\"width: 379px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/Fig-6-1.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-46\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig-6-1-300x278.jpg\" alt=\"The rock cycle shows how different rock groups are interconnected. Metamorphic rocks can come from adding heat and\/or pressure to other metamorphic rock or sedimentary or igneous rocks\" width=\"379\" height=\"352\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig-6-1-300x278.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig-6-1-768x713.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig-6-1-65x60.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig-6-1-225x209.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig-6-1-350x325.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig-6-1.jpg 900w\" sizes=\"auto, (max-width: 379px) 100vw, 379px\" \/><\/a><figcaption id=\"caption-attachment-2480\" class=\"wp-caption-text\">Rock cycle showing the five materials (such as igneous rocks and sediment) and the processes by which one changes into another (such as weathering). (Source: Peter Davis)<\/figcaption><\/figure>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">Metamorphic<\/a> rocks<\/strong>, <em>meta-<\/em> meaning change and &#8211;<em>morphos<\/em>&nbsp;meaning form, is one of the three rock categories in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2671\">rock cycle<\/a> (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/1-understanding-science\/\">Chapter 1<\/a>). <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2684\">Metamorphic rock<\/a> material has been changed by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2689\">temperature<\/a>, pressure, and\/or fluids. <span style=\"font-weight: 400\">The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2671\">rock cycle<\/a> shows that both <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2675\">igneous<\/a> and sedimentary rocks can become <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> rocks. And <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> rocks themselves&nbsp; can be re-metamorphosed. <\/span>Because <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a> is caused by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2576\">plate tectonic<\/a> motion, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2684\">metamorphic rock<\/a> provides geologists with a history book of how past <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2576\">tectonic<\/a> processes shaped our planet.<\/p>\n<h2><span style=\"font-weight: 400\">6.1 Metamorphic Processes<\/span><\/h2>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">Metamorphism<\/a> occurs when solid rock changes in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2831\">composition<\/a> and\/or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2919\">texture<\/a> without the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> crystals melting, which is how <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2675\">igneous rock<\/a> is generated. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">Metamorphic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_3340\">source rocks<\/a>, the rocks that experience the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a>, are called the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2688\">parent rock<\/a> or <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2688\">protolith<\/a><\/strong>, from <em>proto<\/em>&#8211; meaning first, and <em>lithos- <\/em>meaning rock. Most <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> processes take place deep underground, inside the earth\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2580\">crust<\/a>. During <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2688\">protolith<\/a> chemistry is mildly changed by increased <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2689\">temperature<\/a> (heat), a type of pressure called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2917\">confining<\/a> pressure, and\/or chemically reactive fluids. Rock <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2919\">texture<\/a> is changed by heat, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2917\">confining<\/a> pressure, and a type of pressure called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2918\">directed stress<\/a>.<\/p>\n<h3><span style=\"font-weight: 400\">6.1.1&nbsp; Temperature (Heat) &nbsp;<\/span><\/h3>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2689\">Temperature<\/a> measures a substance\u2019s energy\u2014an increase in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2689\">temperature<\/a> represents an increase in energy. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2689\">Temperature<\/a> changes affect the chemical equilibrium or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2702\">cation<\/a> balance in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a>. At high temperatures atoms may vibrate so vigorously they jump from one position to another within the crystal lattice, which remains intact. In other words, this atom swapping can happen while the rock is still solid.<\/p>\n<p>The temperatures of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2684\">metamorphic rock<\/a> lies in between surficial processes (as in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2683\">sedimentary rock<\/a>) and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2672\">magma<\/a> in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2671\">rock cycle<\/a>. Heat-driven <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a> begins at temperatures as cold as 200\u02daC, and can continue to occur at temperatures as high as 700\u00b0C-1,100\u00b0C. Higher temperatures would create <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2672\">magma<\/a>, and thus, would no longer be a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> process.&nbsp;<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2689\">Temperature<\/a> increases with increasing depth in the Earth along a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1175\">geothermal gradient<\/a> (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/4-igneous-processes-and-volcanoes\/\">Chapter 4<\/a>) and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2684\">metamorphic rock<\/a> records these depth-related <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2689\">temperature<\/a> changes.<\/p>\n<h3><span style=\"font-weight: 400\">6.1.2 Pressure<\/span><\/h3>\n<p>Pressure <span style=\"font-weight: 400\">is the force exerted over a unit area on a material. Like heat, pressure can affect the chemical equilibrium of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> in a rock. The pressure that affects <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> rocks can be grouped into <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2917\">confining<\/a> pressure and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2918\">directed stress<\/a>. <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2915\">Stress<\/a><\/strong> is a scientific term indicating a&nbsp;force. <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2916\">Strain<\/a><\/strong> is the result of this <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2915\">stress<\/a>, including <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> changes within <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a>.<\/span><\/p>\n<h4><b>Confining Pressure<\/b><\/h4>\n<figure id=\"attachment_3148\" aria-describedby=\"caption-attachment-3148\" style=\"width: 450px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.1-02-Pressure-vs-Stress.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-432\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.1-02-Pressure-vs-Stress-300x252.png\" alt=\"Pressure is a state where all stresses on a body are equal. The magnitude of these balanced stresses increases with increasing depth within the earth. These stresses can not deform rocks other than to decrease their volume. Pressure is the term used becuase the concept of pressure is used in chemistry, which it the discipline of science used to understand the mineral reactions that occur within the rock. DIRECTED STRESSES s, s, One or more directions of stress are not equal in magnitude and or not in line with each other (non-coaxial). Unlike balanced stresses, the difference in these stresses can deform rocks within the earth.\" width=\"450\" height=\"378\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.1-02-Pressure-vs-Stress-300x252.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.1-02-Pressure-vs-Stress-1024x859.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.1-02-Pressure-vs-Stress-768x644.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.1-02-Pressure-vs-Stress-65x55.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.1-02-Pressure-vs-Stress-225x189.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.1-02-Pressure-vs-Stress-350x294.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.1-02-Pressure-vs-Stress.png 1385w\" sizes=\"auto, (max-width: 450px) 100vw, 450px\" \/><\/a><figcaption id=\"caption-attachment-3148\" class=\"wp-caption-text\">Difference between pressure and stress and how they deform rocks. Pressure (or confining pressure) has equal stress (forces) in all directions and increases with depth under the Earth\u2019s surface. Under directed stress, some stress directions (forces) are stronger than others, and this can deform rocks. (Source: Peter Davis)<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">Pressure exerted on rocks under the surface&nbsp;is due to the simple fact that rocks lie on top of one another. When pressure is exerted from rocks above, it is balanced from below and sides, and is called <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2917\">confining<\/a><\/b><span style=\"font-weight: 400\"> or <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2917\">lithostatic<\/a> pressure<\/b><span style=\"font-weight: 400\">. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2917\">Confining<\/a> pressure has equal pressure on all sides (see figure) and is&nbsp;responsible for causing chemical reactions to occur just like heat. These chemical reactions will cause new <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> to form.&nbsp;<\/span><\/p>\n<p><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2917\">Confining<\/a> pressure is measured in bars and ranges from 1 bar at sea level to around 10,000 bars at the base of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2580\">crust<\/a>. &nbsp;For <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> rocks, pressures range from a relatively low-pressure of 3,000 bars around 50,000 bars, which occurs around 15-35 kilometers below the surface.<\/span><\/p>\n<h4><b>Directed Stress<\/b><\/h4>\n<figure id=\"attachment_3150\" aria-describedby=\"caption-attachment-3150\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2_800px-P535973.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-433 size-medium\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2_800px-P535973-300x225.jpg\" alt=\"Pebbles in quartzite deformed by directed stress\" width=\"300\" height=\"225\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2_800px-P535973-300x225.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2_800px-P535973-768x576.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2_800px-P535973-65x49.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2_800px-P535973-225x169.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2_800px-P535973-350x263.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2_800px-P535973.jpg 800w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3150\" class=\"wp-caption-text\">Pebbles (that used to be spherical or close to spherical) in quartzite deformed by directed stress<\/figcaption><\/figure>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2918\">Directed stress<\/a><\/strong>, also called differential or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2918\">tectonic stress<\/a>, is an unequal balance of forces on a rock in one or more directions (see previous figure). Directed <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2915\">stresses<\/a> are generated by the movement of lithospheric <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2591\">plates<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2915\">Stress<\/a> indicates a type of force acting on rock. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2916\">Strain<\/a> describes the resultant processes caused by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2915\">stress<\/a> and includes <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> changes in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a>. In contrast to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2917\">confining<\/a> pressure, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2918\">directed stress<\/a> occurs at much lower pressures and does not generate chemical reactions that change <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2831\">composition<\/a> and atomic structure. Instead, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2918\">directed stress<\/a> modifies the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2688\">parent rock<\/a> at a mechanical level, changing the arrangement, size, and\/or shape of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> crystals. These crystalline changes create identifying textures, which is shown in the figure below comparing the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1940\">phaneritic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2919\">texture<\/a> of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2675\">igneous<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1962\">granite<\/a> with the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2924\">foliated<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2919\">texture<\/a> of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2932\">gneiss<\/a>.<\/p>\n<figure id=\"attachment_3152\" aria-describedby=\"caption-attachment-3152\" style=\"width: 1024px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.1-03-Granite-vs-Gneiss.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-434 size-large\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.1-03-Granite-vs-Gneiss-1024x443.jpg\" alt=\"Two rocks with very similar colors. One is a granite and another is a gneiss that has aligned dark minerals.\" width=\"1024\" height=\"443\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.1-03-Granite-vs-Gneiss-1024x443.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.1-03-Granite-vs-Gneiss-300x130.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.1-03-Granite-vs-Gneiss-768x332.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.1-03-Granite-vs-Gneiss-65x28.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.1-03-Granite-vs-Gneiss-225x97.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.1-03-Granite-vs-Gneiss-350x151.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.1-03-Granite-vs-Gneiss.jpg 1175w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/a><figcaption id=\"caption-attachment-3152\" class=\"wp-caption-text\">An igneous rock granite (left) and foliated high-temperature and high-pressure metamorphic rock gneiss (right) illustrating a metamorphic texture. (Source: Peter Davis)<\/figcaption><\/figure>\n<p>Directed <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2915\">stresses<\/a> produce rock textures in many ways. Crystals are rotated, changing their orientation in space. Crystals can get fractured, reducing their <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2828\">grain size<\/a>. Conversely, they may grow larger as atoms migrate. Crystal shapes also become deformed. These mechanical changes occur via <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2920\">recrystallization<\/a><\/strong>, which is when <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2815\">dissolve<\/a> from an area of rock experiencing high <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2915\">stress<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2707\">precipitate<\/a> or regrow in a location having lower <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2915\">stress<\/a>. For example, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2920\">recrystallization<\/a> increases <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2828\">grain size<\/a> much like adjacent soap bubbles coalesce to form larger ones. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2920\">Recrystallization<\/a> rearranges <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> crystals without fracturing the rock structure, deforming the rock like silly putty; these changes provide important clues to understanding the creation and movement of deep underground rock <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_3065\">faults<\/a>.<\/p>\n<h3><span style=\"font-weight: 400\">6.1.3 Fluids<\/span><\/h3>\n<p>A third <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> agent is chemically reactive fluids that are expelled by crystallizing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2672\">magma<\/a> and created by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> reactions. These reactive fluids are made of mostly water (H<sub>2<\/sub>O) and carbon dioxide (CO<sub>2<\/sub>), and smaller amounts of potassium (K), sodium (Na), iron (Fe), magnesium (Mg), calcium (Ca), and aluminum (Al). These fluids react with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2688\">protolith<\/a>, changing its chemical equilibrium and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2831\">composition<\/a>, in a process similar to the reactions driven by heat and pressure. In addition to using <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2700\">elements<\/a> found in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2688\">protolith<\/a>, the chemical reaction may incorporate substances contributed by the fluids to create new <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a>. In general, this style of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a>, in which fluids play an important role, is called <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2921\">hydrothermal<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a><\/strong> or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2921\">hydrothermal<\/a> alteration. Water actively participates in chemical reactions and allows extra mobility of the components in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2921\">hydrothermal<\/a> alteration.<\/p>\n<p>Fluids-activated <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a> is frequently involved in creating economically important <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> deposits that are located next to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2675\">igneous<\/a> intrusions or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2672\">magma<\/a> bodies. For example, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_3324\">mining<\/a> districts in the Cottonwood Canyons and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">Mineral<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1461\">Basin<\/a> of northern Utah produce valuable <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_3325\">ores<\/a> such as argentite (silver <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1921\">sulfide<\/a>), galena (lead <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1921\">sulfide<\/a>), and chalcopyrite (copper iron <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1921\">sulfide<\/a>), as well as the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1924\">native<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2700\">element<\/a> gold. These <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> deposits were created from the interaction between a granitic intrusion called the Little Cottonwood Stock and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1971\">country rock<\/a> consisting of mostly <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2851\">limestone<\/a> and dolostone. Hot, circulating fluids expelled by the crystallizing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1962\">granite<\/a> reacted with and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2815\">dissolved<\/a> the surrounding <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2851\">limestone<\/a> and dolostone, precipitating out new <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> created by the chemical reaction. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2921\">Hydrothermal<\/a> alternation of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1956\">mafic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2586\">mantle<\/a> rock, such as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2711\">olivine<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1961\">basalt<\/a>, creates the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2684\">metamorphic rock<\/a> <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2923\">serpentinite<\/a><\/strong>, a member of the serpentine subgroup of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a>. This <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> process happens at mid-ocean <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2630\">spreading centers<\/a> where newly formed <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2581\">oceanic crust<\/a> interacts with seawater.<\/p>\n<p><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/BlackSmoker.jpg\">&lt;img class=&#8221;wp-image-2545&#8243; title=&#8221;By University of Washington; NOAA\/OAR\/OER. (NOAA Photo Library: expl2366) [<\/a><a href=\"\/\/creativecommons.org\/licenses\/by\/2.0&quot;\">CC BY 2.0<\/a> or Public domain], <a href=\"\/\/commons.wikimedia.org\/wiki\/File%3AExpl2366_-_Flickr_-_NOAA_Photo_Library.jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/BlackSmoker-233&#215;300.jpg&#8221; alt=&#8221;There is a large build up of minerals around the vent&#8221; width=&#8221;304&#8243; height=&#8221;392&#8243;&gt; Black smoker hydrothermal vent with a colony of giant (6\u2019+) tube worms.Some <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2921\">hydrothermal<\/a> alterations remove <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2700\">elements<\/a> from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2688\">parent rock<\/a> rather than deposit them. This happens when seawater circulates down through <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1934\">fractures<\/a> in the fresh, still-hot <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1961\">basalt<\/a>, reacting with and removing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> ions from it. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2815\">dissolved<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> are usually ions that do not fit snugly in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2709\">silicate<\/a> crystal structure, such as copper. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a>-laden water emerges from the sea floor via <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2921\">hydrothermal<\/a> vents called <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2922\">black smokers<\/a><\/strong>, named after the dark-colored precipitates produced when the hot <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1187\">vent<\/a> water meets cold seawater. (see Chapter 4, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2675\">Igneous Rock<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1181\">Volcanic<\/a> Processes) Ancient <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2922\">black smokers<\/a> were an important source of copper <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_3325\">ore<\/a> for the inhabitants of Cyprus (Cypriots) as early as 4,000 BCE, and later by the Romans.<\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-37\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-37\" class=\"h5p-iframe\" data-content-id=\"37\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"6.1 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4000\" aria-describedby=\"caption-attachment-4000\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/6.1-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-435\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/6.1-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.1-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.1-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.1-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.1-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.1-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.1-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.1-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.1-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4000\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 6.1 via this QR Code.<\/figcaption><\/figure>\n<h2><span style=\"font-weight: 400\">6.2 Metamorphic textures <\/span><\/h2>\n<p><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">Metamorphic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2919\">texture<\/a> is the description of the shape and orientation of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> grains in a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2684\">metamorphic rock<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2684\">Metamorphic rock<\/a> textures are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2924\">foliated<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2934\">non-foliated<\/a>, or lineated are described below.<\/span><\/p>\n<figure id=\"attachment_3157\" aria-describedby=\"caption-attachment-3157\" style=\"width: 791px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/MetaRx3.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-436 size-large\" title=\"(Source: Belinda Madsen) SLCC\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/MetaRx3-791x1024.png\" alt=\"Table identifying the types of metamorphic rocks.\" width=\"791\" height=\"1024\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/MetaRx3-791x1024.png 791w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/MetaRx3-232x300.png 232w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/MetaRx3-768x994.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/MetaRx3-1187x1536.png 1187w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/MetaRx3-1583x2048.png 1583w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/MetaRx3-65x84.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/MetaRx3-225x291.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/MetaRx3-350x453.png 350w\" sizes=\"auto, (max-width: 791px) 100vw, 791px\" \/><\/a><figcaption id=\"caption-attachment-3157\" class=\"wp-caption-text\">Metamorphic rock identification table. (Source: Belinda Madsen)<\/figcaption><\/figure>\n<h3><span style=\"font-weight: 400\">6.2.1 Foliation and Lineation<\/span><\/h3>\n<p><span style=\"font-weight: 400\"><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2924\">Foliation<\/a><\/strong> is a term used that describes <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> lined up in planes. Certain <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a>, most notably the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1914\">mica<\/a> group, are mostly thin and planar by default. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2924\">Foliated<\/a> rocks typically appear as if the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> are stacked like pages of a book, thus the use of the term \u2018folia\u2019, like a leaf<\/span><span style=\"font-weight: 400\">. Other <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a>, with hornblende being a good example, are longer in one direction, linear like a pencil or a needle, rather than a planar-shaped book. These linear objects can also be aligned within a rock. This is referred to as a <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2925\">lineation<\/a><\/b><span style=\"font-weight: 400\">. Linear crystals, such as hornblende, tourmaline, or stretched <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1915\">quartz<\/a> grains, can be arranged as part of a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2924\">foliation<\/a>, a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2925\">lineation<\/a>, or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2924\">foliation<\/a>\/<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2925\">lineation<\/a> together. If they lie on a plane with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1914\">mica<\/a>, but with no common or preferred direction, this is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2924\">foliation<\/a>. If the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> line up and point in a common direction, but with no planar fabric, this is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2925\">lineation<\/a>. When <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> lie on a plane AND point in a common direction; this is both <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2924\">foliation<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2925\">lineation<\/a>. &nbsp;<\/span><\/p>\n<figure id=\"attachment_3164\" aria-describedby=\"caption-attachment-3164\" style=\"width: 588px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-06-Lineation.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-437\" title=\"Source: Peter Davis, Pacific Lutheran University\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-06-Lineation-300x162.png\" alt=\"Lineation is aligned linear features in a rock. An example in the figure is a bundle of aligned straws.\" width=\"588\" height=\"318\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-06-Lineation-300x162.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-06-Lineation-1024x554.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-06-Lineation-768x415.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-06-Lineation-65x35.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-06-Lineation-225x122.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-06-Lineation-350x189.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-06-Lineation.png 1311w\" sizes=\"auto, (max-width: 588px) 100vw, 588px\" \/><\/a><figcaption id=\"caption-attachment-3164\" class=\"wp-caption-text\">Example of lineation where minerals are aligned like a stack of straws or pencils. (Source: Peter Davis)<\/figcaption><\/figure>\n<figure id=\"attachment_3165\" aria-describedby=\"caption-attachment-3165\" style=\"width: 563px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-05-Foliationlineation.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-438\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-05-Foliationlineation-300x113.jpg\" alt=\"Aligned tourmaline crystals in line with foliation. Foliation is the fine &quot;layers&quot; of the rock.\" width=\"563\" height=\"213\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-05-Foliationlineation-300x113.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-05-Foliationlineation-1024x387.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-05-Foliationlineation-768x290.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-05-Foliationlineation-65x25.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-05-Foliationlineation-225x85.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-05-Foliationlineation-350x132.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-05-Foliationlineation.jpg 1048w\" sizes=\"auto, (max-width: 563px) 100vw, 563px\" \/><\/a><figcaption id=\"caption-attachment-3165\" class=\"wp-caption-text\">An example of foliation WITH lineation. (Source: Peter Davis)<\/figcaption><\/figure>\n<figure id=\"attachment_3167\" aria-describedby=\"caption-attachment-3167\" style=\"width: 538px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-04-Foliation-without-lineation.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-439\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-04-Foliation-without-lineation-300x222.png\" alt=\"Foliated surface displays non-lineated hornblende grains. A cross-section displays a cross section of foliated plagioclase and hornblende\" width=\"538\" height=\"399\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-04-Foliation-without-lineation-300x222.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-04-Foliation-without-lineation-1024x759.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-04-Foliation-without-lineation-768x569.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-04-Foliation-without-lineation-65x48.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-04-Foliation-without-lineation-225x167.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-04-Foliation-without-lineation-350x259.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-04-Foliation-without-lineation.png 1242w\" sizes=\"auto, (max-width: 538px) 100vw, 538px\" \/><\/a><figcaption id=\"caption-attachment-3167\" class=\"wp-caption-text\">An example of foliation WITHOUT lineation. (Source: Peter Davis)<\/figcaption><\/figure>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2924\">Foliated<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> rocks are named based on the style of their foliations. Each rock name has a specific <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2919\">texture <\/a> that defines and distinguishes it, with their descriptions listed below.<\/p>\n<p><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2926\">Slate<\/a><\/b><span style=\"font-weight: 400\"> is a fine-grained <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2684\">metamorphic rock<\/a> that exhibits a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2924\">foliation<\/a> called <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2927\">slaty cleavage<\/a> <\/b><span style=\"font-weight: 400\">that is the flat orientation of the small platy crystals of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1914\">mica<\/a> and chlorite forming perpendicular to the direction of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2915\">stress<\/a><\/span><i><span style=\"font-weight: 400\">.&nbsp;<\/span><\/i><span style=\"font-weight: 400\">The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2926\">slate<\/a> are too small to see with the unaided eye. The thin layers in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2926\">slate<\/a> may resemble sedimentary <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2857\">bedding<\/a>, but they are a result of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2918\">directed stress<\/a> and may lie at angles to the original <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2857\">strata<\/a>. In fact, original sedimentary layering may be partially or completely obscured by the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2924\">foliation<\/a>. Thin slabs of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2926\">slate<\/a> are often used as a building material for roofs and tiles.<\/span><\/p>\n<p><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-Ehemaliger_Schiefertagebau_am_Brand.jpg\">&lt;img class=&#8221;wp-image-3169&#8243; title=&#8221;By Uta Baumfelder at de.wikipedia (Own work) [Public domain], <\/a><a href=\"\/\/commons.wikimedia.org\/wiki\/File%3AEhemaliger_Schiefertagebau_am_Brand.JPG&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-Ehemaliger_Schiefertagebau_am_Brand-300&#215;225.jpg&#8221; alt=&#8221;Rock breaking along flat even planes.&#8221; width=&#8221;383&#8243; height=&#8221;287&#8243;&gt; Slate mine in Germany cleavage.<\/p>\n<figure id=\"attachment_3171\" aria-describedby=\"caption-attachment-3171\" style=\"width: 420px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-07-Foliation-vs-bedding.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-440\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-07-Foliation-vs-bedding-300x200.jpg\" alt=\"Foliation is caused by metamorphism. Bedding is a result of sedimentary processes. They do not have to align.\" width=\"420\" height=\"280\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-07-Foliation-vs-bedding-300x200.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-07-Foliation-vs-bedding-1024x683.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-07-Foliation-vs-bedding-768x512.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-07-Foliation-vs-bedding-65x43.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-07-Foliation-vs-bedding-225x150.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-07-Foliation-vs-bedding-350x233.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-07-Foliation-vs-bedding.jpg 1105w\" sizes=\"auto, (max-width: 420px) 100vw, 420px\" \/><\/a><figcaption id=\"caption-attachment-3171\" class=\"wp-caption-text\">Foliation vs. bedding. Foliation is caused by metamorphism. Bedding is a result of sedimentary processes. They do not have to align. (Source: Peter Davis)<\/figcaption><\/figure>\n<figure id=\"attachment_3174\" aria-describedby=\"caption-attachment-3174\" style=\"width: 377px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-10-Phyllite-with-fold-scaled.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-3174\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-10-Phyllite-with-fold-scaled-1.jpg\" alt=\"A foliated rock with a slight sheen.\" width=\"377\" height=\"283\" \/><\/a><figcaption id=\"caption-attachment-3174\" class=\"wp-caption-text\">Phyllite with a small fold. (Source: Peter Davis)<\/figcaption><\/figure>\n<p><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2928\">Phyllite<\/a> <\/b><span style=\"font-weight: 400\">is a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2924\">foliated<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2684\">metamorphic rock<\/a> in which platy <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> have grown larger and the surface of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2924\">foliation<\/a> shows a sheen from light reflecting from the grains, perhaps even a wavy appearance, called crenulations<\/span><span style=\"font-weight: 400\">. Similar to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2928\">phyllite<\/a> but with even larger grains is the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2924\">foliated<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2684\">metamorphic rock<\/a> <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2929\">schist<\/a><\/b><span style=\"font-weight: 400\">, which has large platy grains visible as individual crystals. Common <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1914\">muscovite<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1914\">biotite<\/a>, and porphyroblasts of garnets. A porphyroblast is a large crystal of a particular <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> surrounded by small grains. <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2930\">Schistosity<\/a><\/b><span style=\"font-weight: 400\"> is a textural description of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2924\">foliation<\/a> created by the parallel alignment of platy visible grains. Some schists are named for their <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> such as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1914\">mica<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2929\">schist<\/a> (mostly micas), garnet <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2929\">schist<\/a> (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1914\">mica<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2929\">schist<\/a> with garnets), and staurolite <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2929\">schist<\/a> (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1914\">mica<\/a> schists with staurolite).<\/span><\/p>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_3176\" aria-describedby=\"caption-attachment-3176\" style=\"width: 413px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-Schist_detail-e1492392805920.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-442\" title=\"Source: By Michael C. Rygel (Own work) [CC BY-SA 3.0 (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0)], via Wikimedia Commons\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-Schist_detail-e1492392805920-300x184.jpg\" alt=\"Schist is a scalely looking foliated metamorphic rock.\" width=\"413\" height=\"253\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-Schist_detail-e1492392805920-300x184.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-Schist_detail-e1492392805920-768x470.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-Schist_detail-e1492392805920-65x40.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-Schist_detail-e1492392805920-225x138.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-Schist_detail-e1492392805920-350x214.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-Schist_detail-e1492392805920.jpg 1011w\" sizes=\"auto, (max-width: 413px) 100vw, 413px\" \/><\/a><figcaption id=\"caption-attachment-3176\" class=\"wp-caption-text\">Schist<\/figcaption><\/figure>\n<figure id=\"attachment_3177\" aria-describedby=\"caption-attachment-3177\" style=\"width: 420px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-11-Muscovite-schist.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-443\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-11-Muscovite-schist-300x165.jpg\" alt=\"Shiny foliated rock with small crystals of red faceted garnet among the foliated micas.\" width=\"420\" height=\"230\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-11-Muscovite-schist-300x165.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-11-Muscovite-schist-1024x562.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-11-Muscovite-schist-768x421.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-11-Muscovite-schist-65x36.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-11-Muscovite-schist-225x123.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-11-Muscovite-schist-350x192.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-11-Muscovite-schist.jpg 1105w\" sizes=\"auto, (max-width: 420px) 100vw, 420px\" \/><\/a><figcaption id=\"caption-attachment-3177\" class=\"wp-caption-text\">Garnet staurolite muscovite schist. (Source: Peter Davis)<\/figcaption><\/figure>\n<p><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2_Gneiss.jpg\">&lt;img class=&#8221;wp-image-3179&#8243; title=&#8221;By No machine-readable author provided. Siim assumed (based on copyright claims). [<\/a><a href=\"\/\/www.gnu.org\/copyleft\/fdl.html&quot;\">GFDL<\/a> or <a href=\"\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;\">CC-BY-SA-3.0<\/a>], <a href=\"\/\/commons.wikimedia.org\/wiki\/File%3AGneiss.jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2_Gneiss-300&#215;181.jpg&#8221; alt=&#8221;Alternating bands of light and dark minerals.&#8221; width=&#8221;354&#8243; height=&#8221;213&#8243;&gt; Gneiss&nbsp;<\/p>\n<p><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2931\">Gneissic banding<\/a>&nbsp;<\/b><span style=\"font-weight: 400\">is a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2924\">foliation<\/a><\/span> <span style=\"font-weight: 400\">in which visible <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2709\">silicate<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> separate into dark and light <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2931\">bands<\/a> or lineations. These grains tend to be coarse and often folded. A rock with this <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2919\">texture<\/a> is called <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2932\">gneiss<\/a><\/b><span style=\"font-weight: 400\">. Since gneisses form at the highest temperatures and pressures, some <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1177\">partial melting<\/a> may occur. This partially melted rock is a transition between <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2675\">igneous<\/a> rocks called a <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2933\">migmatite<\/a><\/b><b>.<\/b><\/p>\n<figure id=\"attachment_2482\" aria-describedby=\"caption-attachment-2482\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/06.2-15-Mt-Blaca-Migmatite-1.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"size-medium wp-image-48\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-15-Mt-Blaca-Migmatite-1-300x225.jpg\" alt=\"Swirling bands of light and dark minerals.\" width=\"300\" height=\"225\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-15-Mt-Blaca-Migmatite-1-300x225.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-15-Mt-Blaca-Migmatite-1-1024x768.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-15-Mt-Blaca-Migmatite-1-768x576.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-15-Mt-Blaca-Migmatite-1-1536x1152.jpg 1536w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-15-Mt-Blaca-Migmatite-1-65x49.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-15-Mt-Blaca-Migmatite-1-225x169.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-15-Mt-Blaca-Migmatite-1-350x263.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-15-Mt-Blaca-Migmatite-1.jpg 1600w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-2482\" class=\"wp-caption-text\">Migmatite, a rock which was partially molten. (Source: Peter Davis)<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2933\">Migmatites<\/a> appear as dark and light <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2931\">banded<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2932\">gneiss<\/a> that may be swirled or twisted some since some <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> started to melt. Thin accumulations of light colored rock layers can occur in a darker rock that are parallel to each other, or even cut across the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2932\">gneissic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2924\">foliation<\/a>. The lighter colored layers are interpreted to be the result of the separation of a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1954\">felsic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2675\">igneous<\/a> melt from the adjacent highly metamorphosed darker layers, or injection of a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1954\">felsic<\/a> melt from some distance away. <\/span><\/p>\n<h3><span style=\"font-weight: 400\">6.2.2 Non-foliated<\/span><\/h3>\n<figure id=\"attachment_3185\" aria-describedby=\"caption-attachment-3185\" style=\"width: 413px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-21-Marble-scaled.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-3185\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-21-Marble-scaled-1.jpg\" alt=\"pink crystallized rock with interlocking crystals\" width=\"413\" height=\"300\" \/><\/a><figcaption id=\"caption-attachment-3185\" class=\"wp-caption-text\">Marble (Source: Peter Davis)<\/figcaption><\/figure>\n<figure id=\"attachment_3188\" aria-describedby=\"caption-attachment-3188\" style=\"width: 420px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.2-20-Baraboo.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-445\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-20-Baraboo-300x275.jpg\" alt=\"Crystallized rock with interlocking crystals.\" width=\"420\" height=\"385\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-20-Baraboo-300x275.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-20-Baraboo-1024x940.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-20-Baraboo-768x705.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-20-Baraboo-1536x1409.jpg 1536w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-20-Baraboo-2048x1879.jpg 2048w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-20-Baraboo-65x60.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-20-Baraboo-225x206.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.2-20-Baraboo-350x321.jpg 350w\" sizes=\"auto, (max-width: 420px) 100vw, 420px\" \/><\/a><figcaption id=\"caption-attachment-3188\" class=\"wp-caption-text\">Baraboo Quartzite<\/figcaption><\/figure>\n<p><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2934\">Non-foliated<\/a><\/b><span style=\"font-weight: 400\"> textures do not have lineations, foliations, or other alignments of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> grains. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2934\">Non-foliated<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> rocks are typically <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2831\">composed<\/a> of just one <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a>, and therefore, usually show the effects of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a> with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2920\">recrystallization<\/a> in which crystals grow together, but with no preferred direction. The two most common examples of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2934\">non-foliated<\/a> rocks are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2935\">quartzite<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2936\">marble<\/a>. <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2935\">Quartzite<\/a> <\/b><span style=\"font-weight: 400\">is a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2684\">metamorphic rock<\/a> from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2688\">protolith<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2834\">sandstone<\/a>. In <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2935\">quartzites<\/a>, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1915\">quartz<\/a> grains from the original <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2834\">sandstone<\/a> are enlarged and interlocked by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2920\">recrystallization<\/a>. A defining characteristic for distinguishing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2935\">quartzite<\/a> from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2834\">sandstone<\/a> is that when broken with a rock hammer, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1915\">quartz<\/a> crystals break across the grains. In a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2834\">sandstone<\/a>, only a thin <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> cement holds the grains together, meaning that a broken piece of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2834\">sandstone<\/a> will leave the grains intact. Because most <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2834\">sandstones<\/a> are rich in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1915\">quartz<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1915\">quartz<\/a> is a mechanically and chemically durable substance, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2935\">quartzite<\/a> is very hard and resistant to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2676\">weathering<\/a>.<\/span><\/p>\n<p><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2936\">Marble<\/a><\/b><span style=\"font-weight: 400\"> is metamorphosed <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2851\">limestone<\/a> (or dolostone) <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2831\">composed<\/a> of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1918\">calcite<\/a> (or dolomite). <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2920\">Recrystallization<\/a> typically generates larger interlocking crystals of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1918\">calcite<\/a> or dolomite. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2936\">Marble<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2935\">quartzite<\/a> often look similar, but these <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> are considerably softer than <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1915\">quartz<\/a>. Another way to distinguish <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2936\">marble<\/a> from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2935\">quartzite<\/a> is with a drop of dilute hydrochloric acid. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2936\">Marble<\/a> will effervesce (fizz) if it is made of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1918\">calcite<\/a>.<\/span><\/p>\n<p><span style=\"font-weight: 400\">A third <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2934\">non-foliated<\/a> rock is <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2937\">hornfels<\/a> <\/b><span style=\"font-weight: 400\">identified by its dense, fine grained, hard, blocky or splintery <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2919\">texture<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2831\">composed<\/a> of several <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2709\">silicate<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a>. Crystals in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2937\">hornfels<\/a> grow smaller with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a>, and become so small that specialized study is required to identify them. These are common around <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1939\">intrusive<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2675\">igneous<\/a> bodies and<\/span><span style=\"font-weight: 400\">&nbsp;are hard to identify. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2688\">protolith<\/a> of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2937\">hornfels<\/a> can be even harder to distinguish, which can be anything from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2837\">mudstone<\/a> to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1961\">basalt<\/a>.<\/span><\/p>\n<p><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Sample_of_Quartzite-e1493780752118.jpg\">&lt;img class=&#8221;wp-image-3191&#8243; title=&#8221;By Manishwiki15 (Own work) [<\/a><a href=\"\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;\">CC BY-SA 3.0<\/a>], <a href=\"\/\/commons.wikimedia.org\/wiki\/File%3ASample_of_Quartzite.JPG&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Sample_of_Quartzite-e1493780752118-300&#215;210.jpg&#8221; alt=&#8221;Interlocking quartz grains in a quartzite.&#8221; width=&#8221;413&#8243; height=&#8221;289&#8243;&gt; Macro view of quartzite. Note the interconnectedness of the grains.<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/640px-CoralPinkSandDunesSand.jpg\">&lt;img class=&#8221;wp-image-3192&#8243; title=&#8221;By Wilson44691 (Own work) [Public domain], <\/a><a href=\"\/\/commons.wikimedia.org\/wiki\/File%3ACoralPinkSandDunesSand.JPG&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/640px-CoralPinkSandDunesSand-300&#215;225.jpg&#8221; alt=&#8221;Undeformed quartz grains do not interlock.&#8221; width=&#8221;420&#8243; height=&#8221;315&#8243;&gt; Unmetamorphosed, unconsolidated sand grains have space between the grains.<\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-38\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-38\" class=\"h5p-iframe\" data-content-id=\"38\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"6.2 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4001\" aria-describedby=\"caption-attachment-4001\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/6.2-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-446\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/6.2-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.2-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.2-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.2-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.2-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.2-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.2-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.2-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.2-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4001\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 6.2 via this QR Code.<\/figcaption><\/figure>\n<h2><span style=\"font-weight: 400\">6.3 Metamorphic Grade<\/span><\/h2>\n<figure id=\"attachment_3194\" aria-describedby=\"caption-attachment-3194\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.4_Garnet_Mica_Schist_Syros_Greece.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-447 size-medium\" title=\"By Graeme Churchard (GOC53) http:\/\/www.flickr.com\/people\/graeme\/ [CC BY 2.0 (http:\/\/creativecommons.org\/licenses\/by\/2.0)], via Wikimedia Commons\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_Garnet_Mica_Schist_Syros_Greece-300x225.jpg\" alt=\"Large weathered garnet crystals in a matrix of platy micas. The garnets are round-shaped with octagonal sides.\" width=\"300\" height=\"225\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_Garnet_Mica_Schist_Syros_Greece-300x225.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_Garnet_Mica_Schist_Syros_Greece-65x49.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_Garnet_Mica_Schist_Syros_Greece-225x169.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_Garnet_Mica_Schist_Syros_Greece-350x263.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_Garnet_Mica_Schist_Syros_Greece.jpg 640w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3194\" class=\"wp-caption-text\">Garnet schist.<\/figcaption><\/figure>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">Metamorphic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2938\">grade<\/a> refers to the range of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> change a rock undergoes, progressing from low (little <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> change) <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2938\">grade<\/a> to high (significant metamorphic change) grade. Low-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2938\">grade<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a> begins at temperatures and pressures just above <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2683\">sedimentary rock<\/a> conditions. The sequence <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2926\">slate<\/a>\u2192<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2928\">phyllite<\/a>\u2192<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2929\">schist<\/a>\u2192<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2932\">gneiss<\/a> illustrates an increasing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2938\">grade<\/a>.<\/p>\n<p>Geologists use <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2939\">index minerals<\/a><\/strong> that form at certain temperatures and pressures to identify <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2938\">grade<\/a>. These <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2939\">index minerals<\/a> also provide important clues to a rock\u2019s sedimentary <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2688\">protolith<\/a> and the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> conditions that created it. Chlorite, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1914\">muscovite<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1914\">biotite<\/a>, garnet, and staurolite are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2939\">index minerals<\/a> representing a respective sequence of low-to-high <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2938\">grade<\/a> rock. The figure shows a <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2941\">phase diagram<\/a><\/strong> of three <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2939\">index minerals<\/a>\u2014sillimanite, kyanite, and andalusite\u2014with the same chemical formula (Al<sub>2<\/sub>SiO<sub>5<\/sub>) but having different crystal structures (<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2940\">polymorphism<\/a><\/strong>) created by different pressure and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2689\">temperature<\/a> conditions.<\/p>\n<div id=\"h5p-39\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-39\" class=\"h5p-iframe\" data-content-id=\"39\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"6.3 Phase diagram\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4003\" aria-describedby=\"caption-attachment-4003\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/6.3-Phase-diagram-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-448\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Phase-diagram-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Phase-diagram-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Phase-diagram-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Phase-diagram-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Phase-diagram-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Phase-diagram-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Phase-diagram-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Phase-diagram-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Phase-diagram-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4003\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this interactive activity via this QR Code.<\/figcaption><\/figure>\n<p>Some <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> rocks are named based on the highest <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2938\">grade<\/a> of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2939\">index mineral<\/a> present. Chlorite <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2929\">schist<\/a> includes the low-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2938\">grade<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2939\">index mineral<\/a> chlorite. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1914\">Muscovite<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2929\">schist<\/a> contains the slightly higher <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2938\">grade<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1914\">muscovite<\/a>, indicating a greater degree of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a>. Garnet <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2929\">schist<\/a> includes the high <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2938\">grade<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2939\">index mineral<\/a> garnet, and indicating it has experienced much higher pressures and temperatures than chlorite.<\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-40\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-40\" class=\"h5p-iframe\" data-content-id=\"40\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"6.3 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4002\" aria-describedby=\"caption-attachment-4002\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/6.3-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-449\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.3-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4002\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 6.3 via this QR Code.<\/figcaption><\/figure>\n<h2><span style=\"font-weight: 400\">6.4 Metamorphic Environments<\/span><\/h2>\n<p><span style=\"font-weight: 400\">As with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2675\">igneous<\/a> processes, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> rocks form at different zones of pressure (depth) and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2689\">temperature<\/a> as shown on the pressure-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2689\">temperature<\/a> (P-T) diagram. The term <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2913\">facies<\/a> <\/b><span style=\"font-weight: 400\">is an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2644\">objective<\/a> description of a rock. In <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> rocks <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2913\">facies<\/a>&nbsp;are groups of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> assemblages. The names of <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2942\">metamorphic facies<\/a><\/b><span style=\"font-weight: 400\"> on the pressure-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2689\">temperature<\/a> diagram reflect <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> assemblages that are stable at these pressures and temperatures and provide information about the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> processes that have affected the rocks. This is useful when interpreting the history of a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2684\">metamorphic rock<\/a>.<\/span><\/p>\n<figure id=\"attachment_3196\" aria-describedby=\"caption-attachment-3196\" style=\"width: 1024px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Fig-6.24-PT-graph.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-450 size-large\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig-6.24-PT-graph-1024x683.png\" alt=\"\" width=\"1024\" height=\"683\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig-6.24-PT-graph-1024x683.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig-6.24-PT-graph-300x200.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig-6.24-PT-graph-768x512.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig-6.24-PT-graph-1536x1024.png 1536w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig-6.24-PT-graph-2048x1365.png 2048w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig-6.24-PT-graph-65x43.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig-6.24-PT-graph-225x150.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig-6.24-PT-graph-350x233.png 350w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/a><figcaption id=\"caption-attachment-3196\" class=\"wp-caption-text\">Pressure-temperature graphs of various metamorphic facies. (Source: Peter Davis)<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">In the late 1800s, British geologist George Barrow mapped zones of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">index minerals<\/a> in different <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> zones of an area that underwent <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2946\">regional metamorphism<\/a><\/span><span style=\"font-weight: 400\">. Barrow outlined a progression of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2939\">index minerals<\/a>, named the Barrovian Sequence, that represents increasing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2938\">grade<\/a>: chlorite (slates and phyllites) -&gt; <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1914\">biotite<\/a> (phyllites and schists) -&gt; garnet (schists) -&gt; staurolite (schists) -&gt; kyanite (schists) -&gt; sillimanite (schists and gneisses).<\/span><\/p>\n<figure id=\"attachment_3199\" aria-describedby=\"caption-attachment-3199\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/1024px-Scotland_metamorphic_zones_EN.svg_.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-medium wp-image-451\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/1024px-Scotland_metamorphic_zones_EN.svg_-300x208.png\" alt=\"Metamorphic zones in Scotland show increasing metamorphic grade across a transect of a deformed mountain range.\" width=\"300\" height=\"208\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1024px-Scotland_metamorphic_zones_EN.svg_-300x208.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1024px-Scotland_metamorphic_zones_EN.svg_-768x532.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1024px-Scotland_metamorphic_zones_EN.svg_-65x45.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1024px-Scotland_metamorphic_zones_EN.svg_-225x156.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1024px-Scotland_metamorphic_zones_EN.svg_-350x242.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/1024px-Scotland_metamorphic_zones_EN.svg_.png 1024w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3199\" class=\"wp-caption-text\">Barrovian sequence in Scotland.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The first of the Barrovian sequence has a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> group that is commonly found in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> greenschist <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2913\">facies<\/a>. Greenschist rocks form under relatively low pressure and temperatures and represent the fringes of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2946\">regional metamorphism<\/a>. The \u201cgreen\u201d part of the name is derived from &nbsp;green <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> like chlorite, serpentine, and epidote, and the \u201c<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2929\">schist<\/a>\u201d part is applied due to the presence of platy <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> such as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1914\">muscovite<\/a>.<\/span><\/p>\n<p><span style=\"font-weight: 400\">Many different styles of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2942\">metamorphic facies<\/a> are recognized, tied to different geologic and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2576\">tectonic<\/a> processes. Recognizing these <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2913\">facies<\/a> is the most direct way to interpret the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> history of a rock. A simplified list of major <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2942\">metamorphic facies<\/a> is given below.<\/span><\/p>\n<h3><span style=\"font-weight: 400\">6.4.1 Burial Metamorphism<\/span><\/h3>\n<p><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2943\">Burial metamorphism<\/a><\/b><span style=\"font-weight: 400\"> occurs when rocks are deeply buried, at depths of more than 2000 meters (1.24 miles)<\/span><span style=\"font-weight: 400\">. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2943\">Burial metamorphism<\/a> commonly occurs in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1463\">sedimentary basins<\/a>, where rocks are buried deeply by overlying <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2678\">sediments<\/a>. As an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1445\">extension<\/a> of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2827\">diagenesis<\/a>, a process that occurs during <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2682\">lithification<\/a> (<a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/5-weathering-erosion-and-sedimentary-rocks\/\">Chapter 5<\/a>), <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2943\">burial metamorphism<\/a> can cause clay <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a>, such as smectite, in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2839\">shales<\/a> to change to another clay <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> illite. Or it can cause <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1915\">quartz<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2834\">sandstone<\/a> to metamorphose into the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2935\">quartzite<\/a> such the Big Cottonwood <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2960\">Formation<\/a> in the Wasatch Range of Utah. This <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2960\">formation<\/a> was deposited as ancient near-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_3195\">shore<\/a> sands in the late <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2209\">Proterozoic<\/a> (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/7-geologic-time\/\">Chapter 7<\/a>), deeply buried and metamorphosed to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2935\">quartzite<\/a>, folded, and later exposed at the surface in the Wasatch Range today. Increase of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2689\">temperature<\/a> with depth in combination with an increase of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2917\">confining<\/a> pressure produces low-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2938\">grade<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> rocks with a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> assemblages indicative of a zeolite <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2913\">facies<\/a><\/span><span style=\"font-weight: 400\">. <\/span><\/p>\n<h3><span style=\"font-weight: 400\">6.4.2 Contact Metamorphism<\/span><\/h3>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2944\">Contact metamorphism<\/a><\/strong> occurs in rock exposed to high <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2689\">temperature<\/a> and low pressure, as might happen when hot <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2672\">magma<\/a> intrudes into or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2673\">lava<\/a> flows over pre-existing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2688\">protolith<\/a>. This combination of high <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2689\">temperature<\/a> and low pressure produces numerous <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2942\">metamorphic facies<\/a>. The lowest pressure conditions produce <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2937\">hornfels<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2913\">facies<\/a>, while higher pressure creates greenschist, amphibolite, or granulite <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2913\">facies<\/a>.<\/p>\n<p>As with all <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2684\">metamorphic rock<\/a>, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2688\">parent rock<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2919\">texture<\/a> and chemistry are major factors in determining the final outcome of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> process, including what <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2939\">index minerals<\/a> are present. Fine-grained <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2839\">shale<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1961\">basalt<\/a>, which happen to be chemically similar, characteristically recrystallize to produce <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2937\">hornfels<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2834\">Sandstone<\/a> (silica) surrounding an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2675\">igneous<\/a> intrusion becomes <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2935\">quartzite<\/a> via <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2944\">contact metamorphism<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2851\">limestone<\/a> (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1917\">carbonate<\/a>) becomes <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2936\">marble<\/a>.<\/p>\n<p><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Metamorphic_Aureole_in_the_Henry_Mountains.jpg\">&lt;img class=&#8221;wp-image-3201&#8243; title=&#8221;By Random Tree (Own work) [<\/a><a href=\"\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en&quot;\">CC0<\/a>], <a href=\"\/\/commons.wikimedia.org\/wiki\/File%3AMetamorphic_Aureole_in_the_Henry_Mountains.JPG&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Metamorphic_Aureole_in_the_Henry_Mountains-300&#215;225.jpg&#8221; alt=&#8221;Altered rock adjacent to an igneous intrusion.&#8221; width=&#8221;185&#8243; height=&#8221;139&#8243;&gt; Contact metamorphism in outcrop.When <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2944\">contact metamorphism<\/a> occurs deeper in the Earth, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a> can be seen as rings of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2913\">facies<\/a> around the intrusion, resulting in <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2945\">aureoles<\/a><\/strong>. These differences in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a> appear as distinct <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2931\">bands<\/a> surrounding the intrusion, as can be seen around the Alta Stock in Little Cottonwood Canyon, Utah. The Alta Stock is a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1962\">granite<\/a> intrusion surrounded first by rings of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2939\">index minerals<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2713\">amphibole<\/a> (tremolite) and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2711\">olivine<\/a> (forsterite), with a ring of talc (dolostone) located further away<span style=\"font-weight: 400\">.<\/span><\/p>\n<h3><span style=\"font-weight: 400\">6.4.3 Regional Metamorphism<\/span><\/h3>\n<p><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2946\">Regional metamorphism<\/a><\/strong> occurs when <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2688\">parent rock<\/a> is subjected to increased <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2689\">temperature<\/a> and pressure over a large area, and is often located in mountain ranges created by converging <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2575\">continental<\/a> crustal <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2591\">plates<\/a>. This is the setting for the Barrovian sequence of rock <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2913\">facies<\/a>, with the lowest <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2938\">grade<\/a> of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a> occurring on the flanks of the mountains and highest <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2938\">grade<\/a> near the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2589\">core<\/a> of the mountain range, closest to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2600\">convergent<\/a> boundary.<\/p>\n<p>An example of an old regional <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> environment is visible in the northern Appalachian Mountains while driving east from New York state through Vermont and into New Hampshire. Along this route the degree of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a> gradually increases from sedimentary <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2688\">parent rock<\/a>, to low-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2938\">grade<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2684\">metamorphic rock<\/a>, then higher-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2938\">grade<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2684\">metamorphic rock<\/a>, and eventually the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2675\">igneous<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2589\">core<\/a>. The rock sequence is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2683\">sedimentary rock<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2926\">slate<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2928\">phyllite<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2929\">schist<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2932\">gneiss<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2933\">migmatite<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1962\">granite<\/a>. In fact, New Hampshire is nicknamed the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1962\">Granite<\/a> State. The reverse sequence can be seen heading east, from eastern New Hampshire to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2890\">coast<\/a><span style=\"font-weight: 400\">.<\/span><\/p>\n<h3><span style=\"font-weight: 400\">6.4.4 Subduction Zone Metamorphism<\/span><\/h3>\n<figure id=\"attachment_3204\" aria-describedby=\"caption-attachment-3204\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.4-25-Blueschist-e1492235808840-scaled.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-3204 size-medium\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4-25-Blueschist-e1492235808840-scaled-1.jpg\" alt=\"A blue rock with bands of silvery mica grains.\" width=\"300\" height=\"225\" \/><\/a><figcaption id=\"caption-attachment-3204\" class=\"wp-caption-text\">Blueschist (Source: Peter Davis)<\/figcaption><\/figure>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2947\">Subduction zone<\/a> metamorphism is a type of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2946\">regional metamorphism<\/a> that occurs when a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2605\">slab<\/a> of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2581\">oceanic crust<\/a> is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2602\">subducted<\/a> under <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2575\">continental crust<\/a> (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/2-plate-tectonics\/\">Chapter 2<\/a>). Because rock is a good insulator, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2689\">temperature<\/a> of the descending <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2581\">oceanic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2605\">slab<\/a> increases slowly relative to the more rapidly increasing pressure, creating a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> environment of high pressure and low <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2689\">temperature<\/a>. Glaucophane, which has a distinctive blue color, is an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2939\">index mineral<\/a> found in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2948\">blueschist<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2913\">facies<\/a> (see <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2942\">metamorphic facies<\/a> diagram). The California <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2890\">Coast<\/a> Range near San Francisco has <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2948\">blueschist<\/a>&#8211;<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2913\">facies<\/a> rocks created by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2602\">subduction<\/a>-zone <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a>, which include rocks made of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2948\">blueschist<\/a>, greenstone, and red <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2849\">chert<\/a>. Greenstone, which is metamorphized <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1961\">basalt<\/a>, gets its color from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2939\">index mineral<\/a> chlorite.<\/p>\n<h3><span style=\"font-weight: 400\">6.4.5 Fault Metamorphism<\/span><\/h3>\n<figure id=\"attachment_3208\" aria-describedby=\"caption-attachment-3208\" style=\"width: 398px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.4-28-Mylonite.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-453\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4-28-Mylonite-300x116.jpg\" alt=\"Layers of shears material with rotated grains.\" width=\"398\" height=\"153\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4-28-Mylonite-300x116.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4-28-Mylonite-65x25.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4-28-Mylonite-225x87.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4-28-Mylonite-350x135.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4-28-Mylonite.jpg 752w\" sizes=\"auto, (max-width: 398px) 100vw, 398px\" \/><\/a><figcaption id=\"caption-attachment-3208\" class=\"wp-caption-text\">Mylonite (Source: Peter Davis)<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">There are a range of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> rocks made along <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_3065\">faults<\/a>. Near the surface, rocks are involved in repeated <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2583\">brittle<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_3065\">faulting<\/a> produce a material called <\/span><i><span style=\"font-weight: 400\">rock flour,<\/span><\/i><span style=\"font-weight: 400\"> which is rock ground up to the particle size of flour used for food.<\/span> <span style=\"font-weight: 400\">At lower depths,<\/span> <span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_3065\">faulting<\/a> create <\/span><b>cataclastites<\/b><span style=\"font-weight: 400\">, chaotically-crushed mixes of rock material with little internal <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2919\">texture<\/a><\/span><span style=\"font-weight: 400\">. At depths below <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2949\">cataclasites<\/a>, where <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2916\">strain<\/a> becomes <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2582\">ductile<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2950\">mylonites<\/a> are formed. <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2950\">Mylonites<\/a><\/b> <span style=\"font-weight: 400\">are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> rocks created by dynamic <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2920\">recrystallization<\/a> through directed <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_3112\">shear forces<\/a>, generally resulting in a reduction of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2828\">grain size<\/a><\/span><span style=\"font-weight: 400\">. When larger, stronger crystals (like <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1916\">feldspar<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1915\">quartz<\/a>, garnet) embedded in a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> matrix are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1447\">sheared<\/a> into an asymmetrical eye-shaped crystal, an <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2951\">augen<\/a> <\/b><span style=\"font-weight: 400\">is formed<\/span><span style=\"font-weight: 400\">.<\/span><\/p>\n<figure id=\"attachment_3211\" aria-describedby=\"caption-attachment-3211\" style=\"width: 540px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.4-29-Augen.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-454\" title=\"Source: Peter Davis\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4-29-Augen.jpg\" alt=\"Rounded mineral grains from shear forces.\" width=\"540\" height=\"221\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4-29-Augen.jpg 601w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4-29-Augen-300x123.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4-29-Augen-65x27.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4-29-Augen-225x92.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4-29-Augen-350x143.jpg 350w\" sizes=\"auto, (max-width: 540px) 100vw, 540px\" \/><\/a><figcaption id=\"caption-attachment-3211\" class=\"wp-caption-text\">Examples of augens. (Source: Peter Davis)<\/figcaption><\/figure>\n<h3><span style=\"font-weight: 400\">6.4.6 Shock Metamorphism<\/span><\/h3>\n<p><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/820qtz.jpg\">&lt;img class=&#8221;wp-image-3212&#8243; title=&#8221;By Glen A. Izett [Public domain], <\/a><a href=\"\/\/commons.wikimedia.org\/wiki\/File%3A820qtz.jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/820qtz-300&#215;253.jpg&#8221; alt=&#8221;A small grain of sand showing a prismatic inside with lines across it.&#8221; width=&#8221;218&#8243; height=&#8221;184&#8243;&gt; Shock lamellae in a quartz grain.&nbsp;<\/p>\n<p><b>Shock<\/b><span style=\"font-weight: 400\"> (also known as impact) <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a><\/b><span style=\"font-weight: 400\"> is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a> resulting from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2202\">meteor<\/a> or other <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1435\">bolide<\/a> impacts, or from a similar high-pressure shock event. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2952\">Shock metamorphism<\/a> is the result of very high pressures (and higher, but less extreme temperatures) delivered relatively rapidly. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2952\">Shock metamorphism<\/a> produces planar <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1448\">deformation<\/a> features, tektites, shatter cones, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1915\">quartz<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2940\">polymorphs<\/a>. <\/span><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2952\">Shock metamorphism<\/a> produces planar <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1448\">deformation<\/a> features (shock <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2860\">laminae<\/a>), which are narrow planes of glassy material with distinct orientations found in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2709\">silicate<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> grains. Shocked <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1915\">quartz<\/a> has planar <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1448\">deformation<\/a> features<\/span><span style=\"font-weight: 400\">.&nbsp;<\/span><\/p>\n<figure id=\"attachment_3213\" aria-describedby=\"caption-attachment-3213\" style=\"width: 187px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.4_ShatterConeCharlevoix1.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-455\" title=\"By JMGastonguay (Own work) [CC BY-SA 4.0 (http:\/\/creativecommons.org\/licenses\/by-sa\/4.0)], via Wikimedia Commons\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_ShatterConeCharlevoix1-300x225.jpg\" alt=\"Shatter cones are cone-shaped features, that show lines that converge to cone shapes.\" width=\"187\" height=\"140\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_ShatterConeCharlevoix1-300x225.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_ShatterConeCharlevoix1-65x49.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_ShatterConeCharlevoix1-225x169.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_ShatterConeCharlevoix1-350x263.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_ShatterConeCharlevoix1.jpg 640w\" sizes=\"auto, (max-width: 187px) 100vw, 187px\" \/><\/a><figcaption id=\"caption-attachment-3213\" class=\"wp-caption-text\">Shatter cone.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">Shatter cones are cone-shaped pieces of rock <\/span><span style=\"font-weight: 400\">created by dynamic branching <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1934\">fractures<\/a> caused by impacts<\/span><span style=\"font-weight: 400\">. While not strictly a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> structure, they are common around <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2952\">shock metamorphism<\/a>. Their diameter can range from microscopic to several meters. Fine-grained rocks with shatter cones show a distinctive horsetail pattern. <\/span><\/p>\n<p><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2952\">Shock metamorphism<\/a> can also produce <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2939\">index minerals<\/a>, though they are typically only found via microscopic analysis. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1915\">quartz<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_3362\">polymorphs<\/a> coesite and stishovite are indicative of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2952\">impact metamorphism<\/a><\/span><span style=\"font-weight: 400\">. As discussed in chapter 3, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2940\">polymorphs<\/a> are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> with the same <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2831\">composition<\/a> but different crystal structures. Intense pressure (&gt; 10 GPa) and moderate to high temperatures (700-1200 \u00b0C) are required to form these <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a>.<\/span><\/p>\n<figure id=\"attachment_3214\" aria-describedby=\"caption-attachment-3214\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/06.4_Two_tektites.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-456 size-medium\" title=\"By JMGastonguay (Own work) [CC BY-SA 4.0 (http:\/\/creativecommons.org\/licenses\/by-sa\/4.0)], via Wikimedia Commons\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_Two_tektites-300x200.jpg\" alt=\"Shatter cones are cone-shaped features, that show lines that converge to cone shapes.\" width=\"300\" height=\"200\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_Two_tektites-300x200.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_Two_tektites-65x43.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_Two_tektites-225x150.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_Two_tektites-350x234.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/06.4_Two_tektites.jpg 640w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3214\" class=\"wp-caption-text\">Tektites<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2952\">Shock metamorphism<\/a> can also produce glass. <strong>Tektites<\/strong> are gravel-size glass grains ejected during an impact event<\/span><span style=\"font-weight: 400\">. They resemble <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1181\">volcanic<\/a> glass but, unlike <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1181\">volcanic<\/a> glass, tektites contain no water or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1943\">phenocrysts<\/a>, and have a different bulk and isotopic chemistry. Tektites contain partially melted <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2958\">inclusions<\/a> of shocked <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">mineral<\/a> grains<\/span><span style=\"font-weight: 400\">. Although all are melt glasses, tektites are also chemically distinct from trinitite, which is produced from thermonuclear detonations<\/span><span style=\"font-weight: 400\">, and fulgurites, which are produced by lightning strikes<\/span><span style=\"font-weight: 400\">. All geologic glasses not derived from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1181\">volcanoes<\/a> can be called with the general term pseudotachylytes<\/span><span style=\"font-weight: 400\">, a name which can also be applied to glasses created by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_3065\">faulting<\/a>. The term pseudo in this context means \u2018false\u2019 or \u2018in the appearance of\u2019, a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1938\">volcanic rock<\/a> called tachylite because the material observed looks like a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1938\">volcanic rock<\/a>,&nbsp;but is produced by significant <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_1447\">shear<\/a> heating. <\/span><\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-41\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-41\" class=\"h5p-iframe\" data-content-id=\"41\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"6.4 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4128\" aria-describedby=\"caption-attachment-4128\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/6.4-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-457 size-thumbnail\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/6.4-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.4-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.4-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.4-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.4-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.4-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.4-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.4-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/6.4-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4128\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 6.4 via this QR Code.<\/figcaption><\/figure>\n<div>\n<figure id=\"attachment_4005\" aria-describedby=\"caption-attachment-4005\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/Metamorphic-Rocks-toast-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-458\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Metamorphic-Rocks-toast-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Metamorphic-Rocks-toast-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Metamorphic-Rocks-toast-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Metamorphic-Rocks-toast-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Metamorphic-Rocks-toast-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Metamorphic-Rocks-toast-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Metamorphic-Rocks-toast-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Metamorphic-Rocks-toast-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Metamorphic-Rocks-toast-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4005\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-1\" title=\"Metamorphic Rocks (&amp; toast)\" width=\"500\" height=\"375\" src=\"https:\/\/www.youtube.com\/embed\/Ncr-46YX-N0?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<\/div>\n<p><iframe loading=\"lazy\" id=\"oembed-2\" title=\"Identifying Metamorphic Rocks -- Earth Rocks!\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/HUydPhIaQQU?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<figure id=\"attachment_4004\" aria-describedby=\"caption-attachment-4004\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/Identifying-Metamorphic-Rock-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-459\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Identifying-Metamorphic-Rock-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Identifying-Metamorphic-Rock-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Identifying-Metamorphic-Rock-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Identifying-Metamorphic-Rock-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Identifying-Metamorphic-Rock-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Identifying-Metamorphic-Rock-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Identifying-Metamorphic-Rock-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Identifying-Metamorphic-Rock-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Identifying-Metamorphic-Rock-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4004\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<h2><span style=\"font-weight: 400\">Summary<\/span><\/h2>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">Metamorphism<\/a> is the process that changes existing rocks (called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2688\">protoliths<\/a>) into new rocks with new <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> and new textures. Increases in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2689\">temperature<\/a> and pressure are the main causes of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">metamorphism<\/a>, with fluids adding important mobilization of materials. The primary way <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> rocks are identified is with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2919\">texture<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2924\">Foliated<\/a> textures come from platy <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> forming planes in a rock, while <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2934\">non-foliated<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> rocks have no internal fabric. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2938\">Grade<\/a> describes the amount of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2915\">metamorphism<\/a> in a rock, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2913\">facies<\/a> are a set of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2687\">minerals<\/a> that can help guide an observer to an interpretation of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> history of a rock. Different <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2576\">tectonic<\/a> or geologic environments cause <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphism<\/a>, including collisions, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2602\">subduction<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_3065\">faulting<\/a>, and even impacts from space.<\/p>\n<h3>Take this quiz to check your comprehension of this Chapter.<\/h3>\n<div id=\"h5p-42\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-42\" class=\"h5p-iframe\" data-content-id=\"42\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Chapter 6 Review\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4080\" aria-describedby=\"caption-attachment-4080\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/Ch.6-Review-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-460 size-thumbnail\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.6-Review-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.6-Review-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.6-Review-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.6-Review-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.6-Review-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.6-Review-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.6-Review-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.6-Review-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.6-Review-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4080\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the review quiz for Chapter 6 via this QR Code.<\/figcaption><\/figure>\n<h2><span style=\"font-weight: 400\">References<\/span><\/h2>\n<div class=\"csl-bib-body\">\n<ol>\n<li class=\"csl-entry\">Bucher, K., and Grapes, R., 2011, Petrogenesis of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> rocks: Springer, 341 p.<\/li>\n<li class=\"csl-entry\">Jeong, I.-K., Heffner, R.H., Graf, M.J., and Billinge, S.J.L., 2003, Lattice dynamics and correlated atomic motion from the atomic pair distribution function: Phys. Rev. B Condens. Matter, v. 67, no. 10, p. 104301.<\/li>\n<li class=\"csl-entry\">Marshak, S., 2009, Essentials of Geology, 3rd or 4th Edition:<\/li>\n<li class=\"csl-entry\">Proctor, B.P., McAleer, R., Kunk, M.J., and Wintsch, R.P., 2013, Post-Taconic tilting and Acadian structural overprint of the classic Barrovian <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_2914\">metamorphic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_461_3135\">gradient<\/a> in Dutchess County, New York: Am. J. Sci., v. 313, no. 7, p. 649\u2013682.<\/li>\n<li class=\"csl-entry\">Timeline of Art History, 2007, Reference Reviews, v. 21, no. 8, p. 45\u201345.<\/li>\n<\/ol>\n<\/div>\n<p><span style=\"font-weight: 400\">&nbsp;<\/span><\/p>\n<p>&nbsp;<\/p>\n<div class=\"glossary\"><span class=\"screen-reader-text\" id=\"definition\">definition<\/span><template id=\"term_461_2689\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2689\"><div tabindex=\"-1\"><p>The measure of the vibrational (kinetic) energy of a substance.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2914\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2914\"><div tabindex=\"-1\"><p>Rocks and minerals that change within the Earth are called metamorphic, changed by heat and pressure. Metamorphism is the name of the process.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2920\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2920\"><div tabindex=\"-1\"><p>The process of changing a mineral without melting.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2687\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2687\"><div tabindex=\"-1\"><p>A natural substance that is typically solid, has a crystalline structure, and is typically formed by inorganic processes. Minerals are the building blocks of most rocks.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2924\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2924\"><div tabindex=\"-1\"><p>A planer alignment of minerals and textures within a rock.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2926\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2926\"><div tabindex=\"-1\"><p>Metamorphic rock with a strong foliation but no visible minerals, derived from mudstones or shales.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2928\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2928\"><div tabindex=\"-1\"><p>A rock more metamorphosed than slate, to the point that microscopic (but larger) mica gives the rock a glow, called a sheen.&nbsp;Crenulation, or small bends\/folds in the foliation can be present.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2929\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2929\"><div tabindex=\"-1\"><p>Rock more metamorphosed than phyllite, to the point that mica grains are visible. Larger porphyroblasts are sometimes present.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2932\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2932\"><div tabindex=\"-1\"><p>A very high grade metamorphic rock, higher grade than schist, with a separation of light and dark minerals.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2939\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2939\"><div tabindex=\"-1\"><p>Minerals that form at a specific range of temperatures and pressures. Using a collection of index minerals narrows down the conditions of rock formation.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2942\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2942\"><div tabindex=\"-1\"><p>A specific set of index minerals tied to specific styles of metamorphism. When these minerals are present, it allows a history of metamorphism to be determined.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2591\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2591\"><div tabindex=\"-1\"><p>A solid part&nbsp;of the lithosphere which moves as a unit, i.e. the entire plate generally moves the same direction at the same speed.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2576\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2576\"><div tabindex=\"-1\"><p>The theory that the outer layer of the Earth (the lithosphere) is broken in several plates, and these plates move relative to one another, causing the major topographic features of Earth (e.g. mountains, oceans) and most earthquakes and volcanoes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2945\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2945\"><div tabindex=\"-1\"><p>A zone of contact metamorphism that surrounds an intrusion. Since intrusions are typically somewhat round in cross section, the pattern of metamorphism is concentric about the intrusion.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2944\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2944\"><div tabindex=\"-1\"><p>Metamorphism that occurs when rocks are next to a hot intrusion of magma.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2921\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2921\"><div tabindex=\"-1\"><p>Metamorphism which occurs with hot fluids going within rocks, altering and changing the rocks.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_3325\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_3325\"><div tabindex=\"-1\"><p>Valuable material in the Earth, typically used for metallic mineral resources.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2671\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2671\"><div tabindex=\"-1\"><p>The process of changing rocks on Earth into different forms, namely igneous, sedimentary, and metamorphic.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2684\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2684\"><div tabindex=\"-1\"><p>Rocks formed via heat and pressure which change the minerals within the rock.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2675\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2675\"><div tabindex=\"-1\"><p>Rocks that are formed from liquid rock, i.e. from volcanic processes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2831\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2831\"><div tabindex=\"-1\"><p>The mineral make up of a rock, i.e. which minerals are found within a rock.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2919\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2919\"><div tabindex=\"-1\"><p>Arrangement of minerals within a rock.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_3340\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_3340\"><div tabindex=\"-1\"><p>A rock that contains material which can be turned into petroleum resources. Organic-rich muds form good source rocks.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2688\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2688\"><div tabindex=\"-1\"><p>The rocks that existed before the changes that lead to a metamorphic rock, i.e. what rock would exist if the metamorphism was reversed.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2580\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2580\"><div tabindex=\"-1\"><p>The outermost chemical layer of the Earth, defined by its low density and higher concentrations of lighter elements. The crust has two types: <strong>continental<\/strong>, which is the thick, more ductile, and lowest density, and <strong>oceanic<\/strong>, which is higher density, more brittle, and thinner.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2917\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2917\"><div tabindex=\"-1\"><p>Non-directional pressure resulting from burial.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2918\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2918\"><div tabindex=\"-1\"><p>Stress that has a strong directional component (unequal), typically creating elongated or flattened features.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2702\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2702\"><div tabindex=\"-1\"><p>A positively-charged ion. In geology, this commonly includes ions of the elements Ca+2, Na+1, K+1, Fe+2,+3, Al+3, and Mg+2.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2683\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2683\"><div tabindex=\"-1\"><p>Rocks that are formed by sedimentary processes, including sediments lithifying and precipitation from solution.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2672\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2672\"><div tabindex=\"-1\"><p>Liquid rock within the Earth.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1175\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1175\"><div tabindex=\"-1\"><p>The average change in temperature that is experienced as material moves into the Earth. Near the surface, this rate is about 25\u00b0C\/km.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2915\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2915\"><div tabindex=\"-1\"><p>Force applied to an object, typically dealing with forces within the Earth.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2916\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2916\"><div tabindex=\"-1\"><p>The deformation that results from application of a stress.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1940\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1940\"><div tabindex=\"-1\"><p>Large, easy-to-see crystals within an igneous rock. This is common in intrusive rocks.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1962\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1962\"><div tabindex=\"-1\"><p>General name of a felsic rock that is intrusive. Has more felsic minerals than mafic minerals.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2828\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2828\"><div tabindex=\"-1\"><p>The average diameter of a grain of sediment, ranging from small, also known as fine-grained (e.g. clay, silt) to large, also known as coarse-grained (e.g. boulder).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2815\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2815\"><div tabindex=\"-1\"><p>The process in which solids (like minerals) are disassociated and the ionic components are dispersed in a liquid (usually water).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2707\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2707\"><div tabindex=\"-1\"><p>The act of a solid coming out of solution, typically resulting from a drop in temperature or a decrease of the dissolving material.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_3065\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_3065\"><div tabindex=\"-1\"><p>Planer feature where two blocks of bedrock move past each other via earthquakes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2700\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2700\"><div tabindex=\"-1\"><p>A group of all atoms with a specific number of protons, having specific, universal, and unique properties.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_3324\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_3324\"><div tabindex=\"-1\"><p>Place where material is extracted from the Earth for human use.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1461\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1461\"><div tabindex=\"-1\"><p>A down-warped feature in the crust.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1921\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1921\"><div tabindex=\"-1\"><p>Minerals bonded via a sulfur (S-2) atom.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1924\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1924\"><div tabindex=\"-1\"><p>Minerals made from just a single element, bonded to itself. Examples include gold, silver, copper, and diamond, which is a native version of carbon.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1971\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1971\"><div tabindex=\"-1\"><p>Term for the underlying lithified rocks that make up the geologic record in an area. This term can sometimes refer to only the deeper, crystalline (non-layered) rocks.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2851\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2851\"><div tabindex=\"-1\"><p>A chemical or biochemical rock made of mainly calcite.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1956\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1956\"><div tabindex=\"-1\"><p>Can refer to a volcanic rock with lower silica composition, or the minerals that make up those rocks, namely olivine, pyroxene, amphibole, and biotite. Mafic rocks are darker in color and contain more minerals that are dark in color, but can contain some plagioclase feldspar. Primary mafic rocks are basalt (extrusive) and gabbro (intrusive).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2586\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2586\"><div tabindex=\"-1\"><p>Middle chemical layer of the Earth, made of mainly iron and magnesium silicates. It is generally denser than the crust (except for older oceanic crust) and less dense than the core.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2711\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2711\"><div tabindex=\"-1\"><p>(Fe,Mg)2SiO4.&nbsp;Typically translucent olive green and equant, with no cleavage. Common in mafic igneous rocks and in the mantle, but easily weathered in surface conditions. Structure is isolated silica tetrahedra. Known as peridot when a gem.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1961\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1961\"><div tabindex=\"-1\"><p>General name of a mafic rock that is extrusive. Generally has a black groundmass color.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2923\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2923\"><div tabindex=\"-1\"><p>Rock formed from hydrothermal alteration of basalt, made of serpentine.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2630\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2630\"><div tabindex=\"-1\"><p>A divergent boundary within an oceanic plate, where new lithosphere and crust is created as the two plates spread apart. Mid-ocean ridge and spreading center are synonyms.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2581\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2581\"><div tabindex=\"-1\"><p>The thin, outer layer of the Earth which makes up the rocky bottom of the ocean basins. It is made of rocks similar to basalt, and as it cools, even become more dense than the upper mantle below.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1934\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1934\"><div tabindex=\"-1\"><p>A break within a rock that has no relative movement between the sides. Caused by cooling, pressure release, tectonic forces, etc.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2709\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2709\"><div tabindex=\"-1\"><p>Mineral group in which the silica tetrahedra, SiO4-4, is the building block.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2922\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2922\"><div tabindex=\"-1\"><p>Mineral chimneys that form at hydrothermal vents.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1187\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1187\"><div tabindex=\"-1\"><p>Opening of a volcano where lava can erupt.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1181\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1181\"><div tabindex=\"-1\"><p>Place where lava is erupted at the surface.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2934\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2934\"><div tabindex=\"-1\"><p>Metamorphic textures that do not have a directional component of its minerals.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1914\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1914\"><div tabindex=\"-1\"><p>X1A2-3Z4O10(OH,\u202fF)2, where commonly X=K, Na, Ca; A=Al, Mg, Fe; Z=Si, Al. Has two more-common occurrences, light-colored (translucent and pearly tan) muscovite, and dark colored biotite. Has one strong cleavage, and is typically seen as sheets, in stacks or \"books.\" Common in many igneous and metamorphic rocks. Structure is two-dimensional sheets of silica tetrahedra in a hexagonal netowork.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2925\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2925\"><div tabindex=\"-1\"><p>Linear alignment of minerals within a rock.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1915\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1915\"><div tabindex=\"-1\"><p>SiO2. Transparent, but can be any color imaginable with impurities. No cleavage, hard, and commonly forms equant masses. Perfect crystals are hexagonal prisms topped with pyramidal shapes. One of the most common minerals, and is found in many different geologic settings, including the dominant component of sand on the surface of Earth. Structure is a three-dimensional network of silica tetrahedra, connected as much as possible to each other.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2927\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2927\"><div tabindex=\"-1\"><p>A microscopic foliation in slate, in which flat slabs and planes of rock develop.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2857\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2857\"><div tabindex=\"-1\"><p>Discernible layers of rock, typically from a sedimentary rock.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2930\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2930\"><div tabindex=\"-1\"><p>Term for coarse grained, visible, platy minerals in a planar fabric, typical of schists.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2931\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2931\"><div tabindex=\"-1\"><p>A separation of light (felsic) and dark (mafic) minerals in higher grade metamorphic rocks like gneiss.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1177\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1177\"><div tabindex=\"-1\"><p>The process of some material being derived from a heterogenous mixture when melting (e.g. rocks). Because all rocks are made of many different components, they have many different melting points. As they are heated, certain easy-to-melt components will be melted first.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2933\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2933\"><div tabindex=\"-1\"><p>A rock transitional between metamorphic and igneous rock, i.e. rocks so metamorphosed that they begin the process of melting.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1954\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1954\"><div tabindex=\"-1\"><p>Can refer to a volcanic rock with higher silica composition, or the minerals that make up those rocks, namely quartz, feldspar (both potassium feldspar and plagioclase feldspar), and muscovite mica. Felsic rocks are lighter in color and contain more minerals that are light in color, but can contain some biotite and amphibole. Primary felsic rocks are rhyolite (extrusive) and granite (intrusive).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2935\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2935\"><div tabindex=\"-1\"><p>A metamorphosed sandstone.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2936\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2936\"><div tabindex=\"-1\"><p>A metamorphosed limestone.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2834\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2834\"><div tabindex=\"-1\"><p>A rock primarily made of sand.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2676\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2676\"><div tabindex=\"-1\"><p>Breaking down rocks into small pieces by chemical or mechanical means.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1918\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1918\"><div tabindex=\"-1\"><p>CaCO3. Pure form is clear, but can take on many different colors with impurities. It is soft, fizzes in acid, and has three cleavages that are not at 90\u00b0. Thus, it can form slanted blocks, though it is visually common to be without any structure. Found in many sedimentary rocks from marine settings, rarely in igneous rocks, in the metamorphic rock marble, but is common as a secondary mineral throughout surface rocks.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2937\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2937\"><div tabindex=\"-1\"><p>A dense, hard metamorphic rock, typically derived from contact metamorphism.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1939\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1939\"><div tabindex=\"-1\"><p>Igneous rock cooling, and thus forming, inside of the Earth, i.e. under the surface.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2837\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2837\"><div tabindex=\"-1\"><p>A rock made of primarily mud, i.e. particles smaller than sand (\u22640.064 mm).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2938\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2938\"><div tabindex=\"-1\"><p>A qualitative measure of the amount of metamorphism that has occurred or the amount of a resource present in an ore.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2941\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2941\"><div tabindex=\"-1\"><p>Chart that show the stability of different phases of a substance at different conditions.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2940\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2940\"><div tabindex=\"-1\"><p>A specific chemical composition that forms different minerals and different temperatures and pressures. Quartz has several different polymorphs, including coesite, tridimite, and stishovite.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2913\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2913\"><div tabindex=\"-1\"><p>A specific set of features that are tied together in an interpretive group. Facies can be based on mineralogy, biologic factors, fossils, rock types, etc.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2644\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2644\"><div tabindex=\"-1\"><p>An observation that is completely free of bias, i.e. anyone and everyone would make the same observation.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2946\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2946\"><div tabindex=\"-1\"><p>Metamorphism that occurs with large-scale tectonic processes, like collision zones.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2943\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2943\"><div tabindex=\"-1\"><p>Metamorphism that is caused by confining pressure and heat, both increasing with depth.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1463\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1463\"><div tabindex=\"-1\"><p>A local or regional depression which allows sediments to accumulate.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2678\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2678\"><div tabindex=\"-1\"><p>Pieces of rock that have been weathered and possibly eroded.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1445\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1445\"><div tabindex=\"-1\"><p>Stresses that pull objects apart into a larger surface area or volume; stretching forces.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2827\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2827\"><div tabindex=\"-1\"><p>Changes in sedimentary rocks due to increased (but low when compared to metamorphism) temperatures and pressures. This can include deposition of new minerals (e.g. limestone converting to dolomite) or dissolution of existing minerals.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2682\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2682\"><div tabindex=\"-1\"><p>The process of turning sediment into a sedimentary rocks, including deposition, compaction, and cementation.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2839\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2839\"><div tabindex=\"-1\"><p>A very fine-grained rock with very thin layering (fissile).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2960\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2960\"><div tabindex=\"-1\"><p>An extensive, distinct, and mapped set of geologic layers.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_3195\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_3195\"><div tabindex=\"-1\"><p>The part of the coastline which is directly related to water-land interaction, specifically the tidal zone and the range of wave base.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2209\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2209\"><div tabindex=\"-1\"><p>Meaning \"earlier life,\" the third eon of Earth's history, starting at 2.5 billion years ago and ending at 541 million years ago. Marked by increasing atmospheric oxygen and the supercontinent Rodinia.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2673\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2673\"><div tabindex=\"-1\"><p>Liquid rock on the surface of the Earth.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1917\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1917\"><div tabindex=\"-1\"><p>Mineral group in which the carbonate ion, CO3-2, is the building block. This can also refer to the rocks that are made from these minerals, namely limestone and dolomite (dolostone).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2713\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2713\"><div tabindex=\"-1\"><p>(RSi4O11)2, where R is a large number of different cations that can sub in. Can be many colors, but the common form, hornblende, is dark brown to black. Has two cleavages at 54\u00b0 and 126\u00b0. Crystals are typically elongated needles or diamond shapes. Common in many igneous rocks and some metamorphic rocks. Structure is a double chain of silica tetrahedra.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2575\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2575\"><div tabindex=\"-1\"><p>The layers of igneous, sedimentary, and metamorphic rocks that form the continents. Continental crust is much thicker than oceanic crust. Continental crust is defined as having higher concentrations of&nbsp;very light elements like K, Na, and Ca, and is the lowest density rocky layer of Earth. Its average composition is similar to granite.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2589\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2589\"><div tabindex=\"-1\"><p>The innermost chemical layer of the Earth, made chiefly of iron and nickel. It has both liquid and solid components.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2600\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2600\"><div tabindex=\"-1\"><p>Place where two plates come together, casing subduction or collision.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2890\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2890\"><div tabindex=\"-1\"><p>The entire area which is related to land-sea interactions.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2947\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2947\"><div tabindex=\"-1\"><p>Metamorphism that occurs in subduction zones, typically lower temperature and higher pressure.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2605\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2605\"><div tabindex=\"-1\"><p>Name given to the subducting plate, where volatiles are driven out at depth, causing volcanism.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2602\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2602\"><div tabindex=\"-1\"><p>A process where an oceanic plate descends bellow a less dense plate, causing the removal of the plate from the surface. Subduction causes the largest earthquakes possible, as the subducting plate can lock as it goes down. Volcanism is also caused as the plate releases volatiles into the mantle, causing melting.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2948\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2948\"><div tabindex=\"-1\"><p>A metamorphic facies of low temperature, high pressure rocks, typified by the rock blueschist, a metamorphic rock containing a blue amphibole called glaucophane.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2849\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2849\"><div tabindex=\"-1\"><p>A very fine grained version of silica deposited with or without microfossils.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2583\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2583\"><div tabindex=\"-1\"><p>A property of solids in which a force applied to an object causes the object to fracture, break, or snap. Most rocks, at low temperatures, are brittle.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2949\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2949\"><div tabindex=\"-1\"><p>A type of breccia that forms in a brittle way within fault zones.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2582\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2582\"><div tabindex=\"-1\"><p>A property of a solid, such that when a force is applied, the solid flows, stretches, or bends along with the force, instead of cracking or breaking. For example, many plastics are ductile.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2950\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2950\"><div tabindex=\"-1\"><p>Fault-formed rock via ductile deformation, deeper within the Earth.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_3112\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_3112\"><div tabindex=\"-1\"><p>Component of the gravitational force which pushes material downslope.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1916\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1916\"><div tabindex=\"-1\"><p>Consisting of three end members:&nbsp;potassium feldspar (K-spar, KAlSi3O8), plagioclase with calcium (CaAl2Si2O8, called anorthite), and plagioclase with sodium (NaAlSi3O8, called albite). Commonly blocky, with two cleavages as ~90\u00b0. Plagioclase is typically more dull white and grey, and K-spar is more vibrant white, orange, or red. The most common mineral found within the crust, and a major component of almost all igneous rocks, some sedimentary rocks, and some metamorphic rocks. Structure is a three-dimensional framework of silica tetrahedra, with locations open for cations (K, Na, Ca).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1447\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1447\"><div tabindex=\"-1\"><p>Stress within an object that causes a side-to-side movement within an internal fabric or weakness.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2951\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2951\"><div tabindex=\"-1\"><p>Strong crystals that do not deform as easily under ductile deformation, and form lens-shaped porphyroblasts.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2202\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2202\"><div tabindex=\"-1\"><p>A stoney and\/or metallic object from our solar system which was never incorporated into a planet and has fallen onto Earth. Meteorite is used for the rock on Earth, meteoroid for the object in space, and meteor as the object travels in Earth's atmosphere.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1435\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1435\"><div tabindex=\"-1\"><p>A large extraterrestrial object, such as a meteor or asteroid, that hits the surface of the Earth.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2952\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2952\"><div tabindex=\"-1\"><p>Metamorphism caused by bolide impacts.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1448\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1448\"><div tabindex=\"-1\"><p>A strain that occurs in a substance in which the item changes shape due to a stress.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2860\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2860\"><div tabindex=\"-1\"><p>Thin (less than 1 cm) beds of rock.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_3362\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_3362\"><div tabindex=\"-1\"><p>Minerals with the same composition and different crystal structures<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1943\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1943\"><div tabindex=\"-1\"><p>A large crystal within an igneous rock. These can be seen within phaneritic and porphyritic rocks.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_2958\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_2958\"><div tabindex=\"-1\"><p>A piece of a rock that is caught up inside of another rock.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_1938\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_1938\"><div tabindex=\"-1\"><p>Igneous rock cooling, and thus forming, outside of the Earth, i.e. on the surface.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_461_3135\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_461_3135\"><div tabindex=\"-1\"><p>Slope of a stream channel.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><\/div>","protected":false},"author":83,"menu_order":6,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[48],"contributor":[],"license":[],"class_list":["post-461","chapter","type-chapter","status-publish","hentry","chapter-type-numberless"],"part":19,"_links":{"self":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters\/461","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/users\/83"}],"version-history":[{"count":3,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters\/461\/revisions"}],"predecessor-version":[{"id":3407,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters\/461\/revisions\/3407"}],"part":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/parts\/19"}],"metadata":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters\/461\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/media?parent=461"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapter-type?post=461"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/contributor?post=461"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/license?post=461"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}