What Is The Degree To Which A Parent Rock Changes During Metamorphism Called?

Identify metamorphic rocks and the steps of the rock wheel related to their formation.

The last blazon of stone is metamorphic rocks. Allow'southward meet what these rocks are like and how they're formed.

What You'll Learn to Do

• Ascertain the characteristics of a metamorphic rock.
• Discuss the result of heat, pressure and deformation on rocks.

Characteristics of Metamorphic Rocks

A metamorphic rock used to exist another blazon of rock, simply it was changed inside the Earth to become a new type of rock. The word metamorphism comes from aboriginal Greek words for "change" (meta) and "form" (morph). The type of rock that a metamorphic rock used to be, prior to metamorphism, is called the protolith. During metamorphism the mineral content and texture of the protolith are changed due to changes in the physical and chemic environment of the rock. Metamorphism tin be acquired by burial, tectonic stress, heating by magma, or alteration by fluids. At advanced stages of metamorphism, it is mutual for a metamorphic rock to develop such a different set up of minerals and such a thoroughly changed texture that it is hard to recognize what the protolith was.

A rock undergoing metamorphism remains a solid stone during the process. Rocks practice non cook during most conditions of metamorphism. At the highest grade of metamorphism, rocks begin to partially melt, at which point the boundary of metamorphic conditions is surpassed and the igneous part of the rock wheel is entered.

Even though rocks remain solid during metamorphism, fluid is more often than not nowadays in the microscopic spaces betwixt the minerals. This fluid phase may play a major function in the chemical reactions that are an of import role of how metamorphism occurs. The fluid usually consists largely of water.

Metamorphic rocks provide a tape of the processes that occurred within Earth every bit the rock was subjected to changing physical and chemic conditions. This gives the geologist literally "inside information" on what occurs within the Earth during such processes as the formation of new mountain ranges, the collision of continents, the subduction of oceanic plates, and the circulation of sea water into hot oceanic crust. Metamorphic rocks are similar probes that have gone downwardly into the Earth and come dorsum, bringing an record of the weather they encountered on their journey in the depths of the Globe.

Figure ane. The platy layers in this large outcrop of metamorphic rock show the effects of force per unit area on rocks during metamorphism.

In the large outcrop of metamorphic rocks in effigy 1, the rocks' platy advent is a result of the process metamorphism. Metamorphism is the addition of oestrus and/or pressure to existing rocks, which causes them to alter physically and/or chemically so that they get a new rock. Metamorphic rocks may alter so much that they may non resemble the original stone.

Metamorphism

Any type of stone—igneous, sedimentary, or metamorphic—tin can become a metamorphic rock. All that is needed is enough heat and/or pressure to alter the existing rock'south physical or chemical makeup without melting the rock entirely.

Figure 2. A foliated metamorphic rock.

Rocks change during metamorphism because the minerals need to be stable under the new temperature and pressure conditions. The need for stability may cause the structure of minerals to rearrange and grade new minerals. Ions may move between minerals to create minerals of different chemical limerick. Hornfels, with its alternating bands of nighttime and calorie-free crystals, is a practiced example of how minerals rearrange themselves during metamorphism. Hornfels is shown in table 1.

Farthermost force per unit area may also pb to foliation, the apartment layers that form in rocks every bit the rocks are squeezed by pressure (figure 2). Foliation normally forms when pressure level is exerted in only i direction. Metamorphic rocks may likewise exist non-foliated. Quartzite and limestone, shown in table half dozen, are nonfoliated.

The 2 main types of metamorphism are both related to heat inside Earth:

1. Regional metamorphism: Changes in enormous quantities of rock over a wide area caused by the extreme pressure from overlying stone or from compression caused by geologic processes. Deep burial exposes the rock to high temperatures.
2. Contact metamorphism: Changes in a stone that is in contact with magma because of the magma's extreme heat.

Factors that Command Metamorphism

The reason rocks undergo metamorphism is that the minerals in a rock are simply stable under a limited range of pressure, temperature, and chemical weather condition. When rocks are subjected to large enough changes in these factors, the minerals volition undergo chemical reactions that result in their replacement past new minerals, minerals that are stable in the new atmospheric condition.

Chemic Composition of the Protolith

The type of rock undergoes metamorphism is a major factor in determing what type of metamorphic rock it becomes. In short the identify of the protolith plays a big role the identity of the metamorphic stone. A fluid stage may introduce or remove chemical substances into or out of the stone during metamorphism, but in virtually metamorphic rock, near of the atoms in the protolith are exist nowadays in the metamorphic rock later metamorphism; the atoms will likely be rearranged into new mineral forms within the stone. Therefore, not only does the protolith determine the initial chemistry of the metamorphic rock, most metamorphic rocks do not modify their bulk (overall) chemical compositions very much during metamorphism. The fact that well-nigh metamorphic rocks retain well-nigh of their original atoms means that even if the rock was and so thoroughly metamorphosed that information technology no longer looks at all similar the protolith, the rock tin be analyzed in terms of its bulk chemic composition to determine what type of stone the protolith was.

Temperature

Temperature is another major factor of metamorphism. There are ii ways to call up about how the temperature of a rock can exist increased as a outcome of geologic processes.

If rocks are buried within the Earth, the deeper they go, the higher the temperatures they experience. This is considering temperature inside the Globe increases along what is called the geothermal gradient, or geotherm for brusque. Therefore, if rocks are only buried deep enough enough sediment, they will experience temperatures loftier enough to cause metamorphism. This temperature is well-nigh 200ºC (approximately 400ºF).

Tectonic processes are another way rocks tin can exist moved deeper along the geotherm. Faulting and folding the rocks of the crust, can movement rocks to much greater depth than simple burial can.

Yet another way a rock in the Earth's crust can have its temperature greatly increased is by the intrusion of magma nearby. Magma intrusion subjects nearby stone to higher temperature with no increase in depth or pressure.

Pressure

Pressure is a measure of the stress, the physical force, being applied to the surface of a textile. Information technology is defined every bit the force per unit of measurement area acting on the surface, in a direction perpendicular to the surface.

Lithostatic pressure is the pressure exerted on a rock by all the surrounding stone. The source of the pressure level is the weight of all the rocks above. Lithostatic pressure increases as depth within the Earth increases and is a uniform stress—the force per unit area applies equally in all directions on the rock.

If pressure level does non utilize equally in all directions, differential stress occurs. There are 2 types of differential stress.

Normal stress compresses (pushes together) rock in one direction, the direction of maximum stress. At the same time, in a perpendicular management, the rock undergoes tension (stretching), in the management of minimum stress.

Shear stress pushes one side of the rock in a management parallel to the side, while at the same time, the other side of the rock is being pushed in the opposite direction.

Differential stress has a major influence on the the advent of a metamorphic rock. Differential stress tin flatten pre-existing grains in the stone, equally shown in the diagram below.

Metamorphic minerals that grow under differential stress volition have a preferred orientation if the minerals have diminutive structures that tend to brand them form either flat or elongate crystals. This will be particularly apparent for micas or other sheet silicates that abound during metamorphism, such as biotite, muscovite, chlorite, talc, or serpentine. If any of these flat minerals are growing under normal stress, they will grow with their sheets oriented perpendicular to the direction of maximum compression. This results in a rock that can be hands broken along the parallel mineral sheets. Such a rock is said to exist foliated, or to have foliation.

Fluids

Whatever open space between the mineral grains in a rock, notwithstanding microscopic, may contain a fluid phase. Most unremarkably, if in that location is a fluid phase in a stone during metamorphism, it volition be a hydrous fluid, consisting of water and things dissolved in the h2o. Less unremarkably, it may be a carbon dioxide fluid or some other fluid. The presence of a fluid stage is a major cistron during metamorphism because it helps determine which metamorphic reactions volition occur and how fast they will occur. The fluid phase can also influence the rate at which mineral crystals deform or change shape. Most of this influence is due to the dissolved ions that laissez passer in and out of the fluid phase. If during metamorphism enough ions are introduced to or removed from the rock via the fluid to change the bulk chemical limerick of the stone, the rock is said to have undergone metasomatism. However, most metamorphic rocks do non undergo sufficient change in their majority chemistry to be considered metasomatic rocks.

Time

Virtually metamorphism of rocks takes place slowly inside the Earth. Regional metamorphism takes identify on a timescale of millions of years. Metamorphism usually involves slow changes to rocks in the solid state, as atoms or ions lengthened out of unstable minerals that are breaking down in the given pressure and temperature weather condition and migrate into new minerals that are stable in those conditions. This type of chemical reaction takes a long time.

Grades of Metamorphism

Metamorphic grade refers to the general temperature and force per unit area conditions that prevailed during metamorphism. Equally the pressure and temperature increase, rocks undergo metamorphism at higher metamorphic grade. Rocks changing from ane type of metamorphic stone to another as they encounter higher grades of metamorphism are said to be undergoing prograde metamorphism.

Low-form metamorphism takes place at approximately 200–320 ºC and relatively depression pressure. This is non far across the conditions in which sediments become lithified into sedimentary rocks, and it is mutual for a depression-grade metamorphic rock to look somewhat like its protolith. Low form metamorphic rocks tend to characterized past an abundance of hydrous minerals, minerals that contain h2o within their crystal structure. Examples of depression grade hydrous minerals include clay, serpentine, and chlorite. Nether low course metamorphism many of the metamorphic minerals will not grow large enough to be seen without a microscope.

Medium-grade metamorphism takes identify at approximately at 320–450 ºC and at moderate pressures. Depression form hydrous minerals are replaced past micas such equally biotite and muscovite, and non-hydrous minerals such every bit garnet may grow. Garnet is an example of a mineral which may form porphyroblasts, metamorphic mineral grains that are larger in size and more equant in shape (nearly the same bore in all directions), thus continuing out amidst the smaller, flatter, or more elongate minerals.

High-grade metamorphism takes identify at temperatures above most 450 ºC. Micas tend to break down. New minerals such as hornblende will form, which is stable at higher temperatures. Notwithstanding, as metamorphic grade increases to fifty-fifty higher grade, all hydrous minerals, which includes hornblende, may interruption down and exist replaced past other, higher-temperature, non-hydrous minerals such every bit pyroxene.

Alphabetize Minerals

Index minerals, which are indicators of metamorphic class. In a given stone type, which starts with a item chemical composition, lower-grade alphabetize minerals are replaced by college-grade index minerals in a sequence of chemical reactions that proceeds as the stone undergoes prograde metamorphism. For case, in rocks made of metamorphosed shale, metamorphism may prograde through the following alphabetize minerals:

• chlorite characterizes the lowest regional metamorphic grade
• biotite replaces chlorite at the adjacent metamorphic class, which could be considered medium-depression course
• garnet appears at the side by side metamorphic grade, medium grade
• staurolite marks the next metamorphic course, which is medium-high class
• sillimanite is a characteristic mineral of high class metamorphic rocks

Alphabetize minerals are used by geologists to map metamorphic form in regions of metamorphic rock. A geologist maps and collects rock samples across the region and marks the geologic map with the location of each rock sample and the type of index mineral it contains. By drawing lines around the areas where each type of index mineral occurs, the geologist delineates the zones of different metamorphic grades in the region. The lines are known as isograds.

Types of Metamorphism

Regional Metamorphism

Regional metamorphism occurs where large areas of rock are subjected to large amounts of differential stress for long intervals of fourth dimension, weather condition typically associated with mount building. Mountain building occurs at subduction zones and at continental collision zones where ii plates each bearing continental crust, converge upon each other.

Well-nigh foliated metamorphic rocks—slate, phyllite, schist, and gneiss—are formed during regional metamorphism. As the rocks become heated at depth in the Earth during regional metamorphism they go ductile, which means they are relatively soft even though they are all the same solid. The folding and deformation of the rock while information technology is ductile may greatly distort the original shapes and orientations of the rock, producing folded layers and mineral veins that have highly deformed or fifty-fifty convoluted shapes. The diagram below shows folds forming during an early on stage of regional metamorphism, along with development of foliation, in response to normal stress.

The photograph below shows loftier-grade metamorphic rock that has undergone several stages of foliation development and folding during regional metamorphism, and may fifty-fifty have reached such a high temperature that it began to cook.

Contact Metamorphism

Contact metamorphism occurs to solid rock next to an igneous intrusion and is caused by the heat from the nearby body of magma. Because contact metamorphism is not acquired by changes in pressure or by differential stress, contact metamorphic rocks do not become foliated. Where intrusions of magma occur at shallow levels of the crust, the zone of contact metamorphism around the intrusion is relatively narrow, sometimes only a few m (a few anxiety) thick, ranging up to contact metamorphic zones over 1000 1000 (over 3000 feet) beyond around larger intrusions that released more heat into the adjacent chaff. The zone of contact metamorphism surrounding an igneous intrusion is called the metamorphic aureole. The rocks closest to the contact with the intrusion are heated to the highest temperatures, so the metamorphic grade is highest there and diminishes with increasing distance away from the contact. Because contact metamorphism occurs at shallow to moderate depths in the crust and subjects the rocks to temperatures up to the verge of igneous conditions, information technology is sometimes referred to as loftier-temperature, low-pressure metamorphism. Hornfels, which is a hard metamorphic rock formed from fine-grained clastic sedimentary rocks, is a common product of contact metamorphism.

Hydrothermal Metamorphism

Hydrothermal metamorphism is the result of all-encompassing interaction of rock with high-temperature fluids. The difference in composition between the existing rock and the invading fluid drives the chemical reactions. The hydrothermal fluid may originate from a magma that intruded nearby and caused fluid to circulate in the nearby crust, from circulating hot groundwater, or from ocean h2o. If the fluid introduces substantal amounts of ions into the rock and removes substantial amounts of ions from it, the fluid has metasomatized the rock—changed its chemical composition.

Body of water h2o that penetrates hot, croaky oceanic crust and circulates as hydrothermal fluid in ocean floor basalts produces extensive hydrothermal metamorphism adjacent to mid-body of water spreading ridges and other ocean-floor volcanic zones. Much of the basalt subjected to this type of metamorphism turns into a blazon of metamorphic rock known as greenschist. Greenschist contains a set of minerals, some of them green, which may include chlorite, epidote, talc, Na-plagioclase, or actinolite. The fluids eventually escape through vents in the ocean flooring known as black smokers, producing thick deposits of minerals on the sea floor around the vents.

Burying Metamorphism

Burial metamorphism occurs to rocks buried below sediments to depths that exceed the weather condition in which sedimentary rocks form. Considering rocks undergoing burial metamorphism encounter the uniform stress of lithostatic pressure level, not differential pressure, they do not develop foliation. Burial metamorphism is the lowest grade of metamorphism. The main type of mineral that usually grows during burial metamorphism is zeolite, a group of low-density silicate minerals. It usually requires a strong microscope see the small grains of zeolite minerals that course during burial metamorphism.

Subduction Zone Metamorphism

During subduction, a tectonic plate, consisting of oceanic crust and lithospheric pall, is recycled dorsum into the deeper mantle. In almost subduction zones the subducting plate is relatively cold compared with the high temperature it had when first formed at a mid-body of water spreading ridge. Subduction takes the rocks to great depth in the Earth relatively chop-chop. This produces a characteristic type of metamorphism, sometimes called high-pressure, depression-temperature (high-P, low-T) metamorphism, which only occurs deep in a subduction zone. In oceanic basalts that are part of a subducting plate, the high-P, low-T atmospheric condition create a distinctive ready of metamorphic minerals including a type of amphibole, called glaucophane, that has a blue colour. Blueschist is the name given to this type of metamorphic stone. Blueschist is generally interpreted equally having been produced inside a subduction zone, fifty-fifty if the plate boundaries have later shifted and that location is no longer at a subduction zone.

Metamorphic Facies

Much as the minerals and textures of sedimentary rocks can be used as windows to run across into the surroundings in which the sediments were deposited on the World's surface, the minerals and textures of metamorphic rocks provide windows through which we view the conditions of pressure level, temperature, fluids, and stress that occurred within the Earth during metamorphism. The pressure and temperature atmospheric condition under which specific types of metamorphic rocks grade has been adamant by a combination labratory experiments, physics-based theoretical calculations, along with testify in the textures of the rocks and their field relations as recorded on geologic maps. The knowledge of temperatures and pressures at which item types of metamorphic rocks course led to the concept of metamorphic facies. Each metamorphic facies is represented by a specific type of metamorphic stone that forms under a specific force per unit area and temperature conditions.

Fifty-fifty though the name of the each metamorphic facies is taken from a type of rock that forms nether those conditions, that is not the only blazon of rock that volition form in those conditions. For example, if the protolith is basalt, it volition turn into greenschist under greenschist facies conditions, and that is what facies is named for. However, if the protolith is shale, a muscovite-biotite schist, which is not greenish, will course instead. If it tin be determined that a muscovite-biotite schist formed at effectually 350ºC temperature and 400 MPa pressure, information technology can be stated that the rock formed in the greenschist facies, fifty-fifty though the rock is not itself a greenschist.

The diagram below shows metamorphic facies in terms of pressure and temperature condiditons within the Globe. Earth's surface conditions are near the acme left corner of the graph at well-nigh 15ºC which is the average temperature at Earth'southward surface and 0.1 MPa (megapascals), which is almost the average atmospheric pressure on the Earth'south surface. Just as atmospheric pressure comes from the weight of all the air above a point on the Earth's surface, pressure level inside the Globe comes from the weight of all the stone to a higher place a given depth. Rocks are much denser than air and MPa is the unit most usually uses to express pressures inside the Earth. One MPa equals nearly ten atmospheres. A pressure of g MPa corresponds to a depth of about 35 km inside the Globe. Although pressure inside the Earth is adamant past the depth, temperature depends on more than than depth. Temperature depends on the heat flow, which varies from location to location. The way temperature changes with depth within the Globe is called the geothermal slope, geotherm for brusk. In the diagram below, three different geotherms are marked with dashed lines. The three geotherms represent different geological settings in the Globe.

High-pressure, low-temperature geotherms occurs in subduction zones. As the diagram shows, rocks undergoing prograde metamorphism in subduction zones volition be subjected to zeolite, blueschist, and ultimately eclogite facies conditions.

High-temperature, low-pressure level geotherms occur in the vicinity of igneous intrusions in the shallow crust, underlying a volcanically agile expanse. Rocks that take their pressure level and temperature weather condition increased along such a geotherm will metamorphose in the hornfels facies and, if information technology gets hot plenty, in the granulite facies.

Blueschist facies and hornfels facies are associated with unusual geothermal gradients. The most common conditions in the Earth are establish along geotherms between those two extremes. Most regional metamorphic rocks are formed in conditions within this range of geothermal gradients, passing through the greenschist facies to the amphibolites facies. At the maximum pressures and temperatures the rocks may come across within the Earth in this range of geotherms, they volition enter either the granulite or eclogite facies. Regionally metamorphosed rocks that contain hydrous fluids will begin to melt before they pass beyond the amphibolite facies.

Types of Metamorphic Rocks

Metamorphic rock fall into ii categories, foliated and unfoliated. Most foliated metamorphic rocks originate from regional metamorphism. Some unfoliated metamorphic rocks, such equally hornfels, originate only past contact metamorphism, but others can originate either by contact metamorphism or past regional metamorphism. Quartz and marble are prime examples of unfoliated that tin can be produced past either regional or contact metamorphism. Both rock types consist of metamorphic minerals that do not have flat or elongate shapes and thus cannot get layered even if they are produced under differential stress.

A geologist working with metamorphic rocks collects the rocks in the field and looks for the patterns the rocks course in outcrops likewise as how those outcrops are related to other types of rock with which they are in contact. Field evidence is often required to know for sure whether rocks are products of regional metamorphism, contact metamorphism, or some other blazon of metamorphism. If only looking at rock samples in a laboratory, one can be sure of the type of metamorphism that produced a foliated metamorphic rock such as schist or gneiss, or a hornfels, which is unfoliated, but one cannot be sure of the blazon of metamorphism that produced an unfoliated marble or quartzite.

Foliated Metamorphic Rocks

Foliated metamorphic rocks are named for their style of foliation. Yet, a more consummate name of each particular blazon of foliated metamorphic rock includes the main minerals that the rock comprises, such equally biotite-garnet schist rather than only schist.

• slate—slates form at low metamorphic form past the growth of fine-grained chlorite and clay minerals. The preferred orientation of these canvas silicates causes the rock to easily break along parallel planes, giving the rock a slaty cleavage. Some slate breaks into such extensively flat sheets of rock that it is used equally the base of puddle tables, beneath a layer of rubber and felt. Roof tiles are also sometimes fabricated of slate.
• phyllite—phyllite is a depression-medium grade regional metamorphic rock in which the clay minerals and chlorite take been at least partly replaced by mica mica minerals, muscovite and biotite. This gives the surfaces of phyllite a satiny luster, much brighter than the surface of a piece of slate. It is also common for the differential stresses under which phyllite forms to have produced a set of folds in the stone, making the foliation surfaces wavy or irregular, in contrast to the often perfectly flat surfaces of slaty cleavage.
• schist—the size of mineral crystals tends to abound larger with increasing metamorphic grade. Schist is a product of medium grades of metamorphism and is characterized past visibly prominent, parallel sheets of mica or like sheet silicates, commonly either muscovite or biotite, or both. In schist, the sheets of mica are usually arranged in irregular planes rather than perfectly flat planes, giving the rock a schistose foliation (or simply schistosity). Schist often contains more than just micas amid its minerals, such every bit quartz, feldspars, and garnet.
• amphibolite—a poorly foliated to unfoliated mafic metamorphic rock, usually consisting largely of the mutual black amphibole known equally hornblende, plus plagioclase, plus or minus biotite and maybe other minerals; information technology usually does not contain whatever quartz. Amphibolite forms at medium-high metamorphic grades. Amphibolite is also listed below in the section on unfoliated metamorphic rocks.
• gneiss—similar the give-and-take schist, the word gneiss is originated from the High german; it is pronounced "squeamish." Equally metamorphic course continue to increment, sheet silicates go unstable and nighttime minerals such as hornblende or pyroxene start to grow. The nighttime-colored minerals tend to class carve up bands or stripes in the rock, giving it a gneissic foliation of dark and light streaks. Gneiss is a high-course metamorphic rock. Many types of gneiss expect somewhat like granite, except that the gneiss has dark and light stripes whereas in granite randomly oriented and distributed minerals with no stripes or layers.
• migmatite—a combination of high-grade regional metamorphic rock – usually gneiss or schist – and granitic igneous rock. The granitic stone in migmatite probably originated from partial melting of some of the metamorphic stone, though in some migmatites the granite may take intruded the rock from deeper in the chaff. In migmatite you can encounter metamorphic rock that has reached the limits of metamorphism and begun transitioning into the igneous stage of the rock bicycle by melting to form magma.

Names of different styles of foliation come from the mutual rocks that exhibit such foliation:

• slate has slaty foliation
• phyllite has phyllitic foliation
• schist has schistose foliation
• gneiss has gneissic foliation (also called gneissose foliation)

Nonfoliated Metamorphic Rocks

Nonfoliated metamorphic rocks lack a planar (oriented) textile, either because the minerals did not grow under differential stress, or because the minerals that grew during metamorphism are not minerals that have elongate or flat shapes. Because they lack foliation, these rocks are named entirely on the basis of their mineralogy.

• hornfels—hornfels are very hard rocks formed by contact metamorphism of shale, siltstone, or sandstone. The rut from the nearby magma "bakes" the sedimentary rocks and recrystallizes the minerals in them into a new texture that no longer breaks hands forth the original sedimentary bedding planes. Depending on the limerick of the rock and the temperature reached, minerals indicative of loftier metamorphic grade such as pyroxene may occur in some hornfels, though many hornfels take minerals indicating medium grade metamorphism.
• amphibolite—amphibolites are dark-colored rocks with amphibole, commonly the mutual black amphibole known as hornblende, as their most abundant mineral, forth with plagioclase and possibly other minerals, though usually no quartz. Amphibolites are poorly foliated to unfoliated and form at medium to medium-high grades of metamorphism from basalt or gabbro.
• quartzite—quartzite is a metamorphic stone fabricated nearly entirely of quartz, for which the protolith was quartz arenite. Because quartz is stable over a wide range of pressure level and temperature, little or no new minerals form in quartzite during metamorphism. Instead, the quartz grains recrystallize into a denser, harder rock than the original sandstone. If struck past a rock hammer, quartzite will commonly break right through the quartz grains, rather than around them as when quartz arenite is cleaved.
• marble—marble is a metamorphic rock fabricated up almost entirely of either calcite or dolomite, for which the protolith was either limestone or dolostone, respectively. Marbles may have bands of dissimilar colors which were deformed into convoluted folds while the rock was ductile. Such marble is often used as decorative stone in buildings. Some marble, which is considered amend quality stone for carving into statues, lacks color bands.

Table 1. Common Metamorphic Rocks and Their Parent Stone
Pic	Stone Name	Blazon of Metamorphic Stone	Comments
	Slate	Foliated	Metamorphism of shale
	Phyllite	Foliated	Metamorphism of slate, but under greater heat and pressure level than slate
	Schist	Foliated	Oftentimes derived from metamorphism of claystone or shale; metamorphosed under more than heat and pressure than phyllite
	Gneiss	Foliated	Metamorphism of various different rocks, under extreme conditions of heat and pressure
	Hornfels	Non-foliated	Contact metamorphism of diverse dissimilar rock types
	Quartzite	Not-foliated	Metamorphism of sandstone
	Marble	Non-foliated	Metamorphism of limestone
	Metaconglomerate	Not-foliated	Metamorphism of conglomerate

Metamorphic Rock Nomenclature

Foliated Metamorphic Rocks
Crystal Size	Mineralogy	Protolith	Metamorphism	Rock Name
very fine	clay minerals	shale	depression grade regional	slate
fine	clay minerals, biotite, muscovite	shale	low class regional	phyllite
medium to coarse	biotite, muscovite, quartz, garnet, plagioclase	shale, basalt	medium grade regional	schist
medium to coarse	amphibole, plagioclase, biotite	basalt	medium form regional	amphibolite (Note: may exist unfoliated)
medium to coarse	plagioclase, orthoclase, quartz, biotite, amphibole, pyroxene	basalt, granite, shale	high class regional	gneiss
Unfoliated Metamorphic Rocks
Crystal Size	Mineralogy	Protolith	Metamorphism	Rock Name
fine to coarse	quartz	sandstone	regional or contact	quartzite
fine to coarse	calcite	limestone	regional or contact	marble
fine	pyroxene, amphibole, plagioclase	shale	contact	hornfels

Annotation that not all minerals listed in the mineralogy column volition be present in every rock of that type and that some rocks may take minerals not listed here.

Uses of Metamorphic Rocks

Figure 3. Marble is used for decorative items and in art.

Quartzite and marble are ordinarily used for building materials and artwork. Marble is beautiful for statues and decorative items such equally vases (meet an example in figure iii). Ground up marble is as well a component of toothpaste, plastics, and paper.

Quartzite is very hard and is ofttimes crushed and used in building railroad tracks (see figure 4). Schist and slate are sometimes used every bit edifice and landscape materials. Graphite, the "atomic number 82" in pencils, is a mineral normally found in metamorphic rocks.

Figure 4. Crushed quartzite is sometimes placed nether railroad tracks because information technology is very difficult and durable.

Identifying Metamorphic Rocks

This video discusses how to identify a metamorphic rocks:

Bank check Your Understanding

Respond the question(s) beneath to run into how well you understand the topics covered in the previous section. This short quiz doesnon count toward your class in the form, and you can retake it an unlimited number of times.

Use this quiz to cheque your understanding and decide whether to (i) study the previous department farther or (ii) move on to the adjacent section.

Source: https://courses.lumenlearning.com/wmopen-geology/chapter/outcome-metamorphic-rocks/

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