Which Of The Following Changes In Conditions Would Represent Heating During Burial?

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

The last blazon of rock is metamorphic rocks. Let's see what these rocks are like and how they're formed.

What You'll Learn to Practice

• Define the characteristics of a metamorphic rock.
• Discuss the effect of estrus, pressure and deformation on rocks.

Characteristics of Metamorphic Rocks

A metamorphic rock used to be another type of rock, but it was changed inside the World 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 chemical environment of the rock. Metamorphism tin be caused by burial, tectonic stress, heating by magma, or alteration by fluids. At advanced stages of metamorphism, it is common for a metamorphic rock to develop such a different fix of minerals and such a thoroughly changed texture that information technology is difficult to recognize what the protolith was.

A rock undergoing metamorphism remains a solid stone during the process. Rocks do not cook during virtually conditions of metamorphism. At the highest course of metamorphism, rocks begin to partially melt, at which point the purlieus of metamorphic atmospheric condition is surpassed and the igneous function of the stone bicycle is entered.

Even though rocks remain solid during metamorphism, fluid is generally present in the microscopic spaces betwixt the minerals. This fluid phase may play a major function in the chemic reactions that are an important part of how metamorphism occurs. The fluid usually consists largely of water.

Metamorphic rocks provide a record of the processes that occurred inside Earth every bit the rock was subjected to changing physical and chemical weather. This gives the geologist literally "inside data" on what occurs within the Earth during such processes equally the formation of new mountain ranges, the collision of continents, the subduction of oceanic plates, and the circulation of body of water h2o into hot oceanic crust. Metamorphic rocks are like probes that accept gone downward into the Earth and come dorsum, bringing an record of the atmospheric condition they encountered on their journey in the depths of the Earth.

Figure 1. The platy layers in this large outcrop of metamorphic stone bear witness the furnishings of pressure on rocks during metamorphism.

In the large outcrop of metamorphic rocks in figure i, the rocks' platy appearance is a upshot of the process metamorphism. Metamorphism is the addition of heat and/or pressure to existing rocks, which causes them to change physically and/or chemically and then that they get a new rock. Metamorphic rocks may alter so much that they may not resemble the original rock.

Metamorphism

Any type of rock—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's physical or chemical makeup without melting the rock entirely.

Effigy 2. A foliated metamorphic rock.

Rocks change during metamorphism considering the minerals demand to be stable under the new temperature and pressure atmospheric condition. The need for stability may cause the structure of minerals to rearrange and form new minerals. Ions may move between minerals to create minerals of dissimilar chemical composition. Hornfels, with its alternate bands of dark and calorie-free crystals, is a good example of how minerals rearrange themselves during metamorphism. Hornfels is shown in tabular array 1.

Extreme pressure may also lead to foliation, the flat layers that course in rocks as the rocks are squeezed by pressure level (figure 2). Foliation unremarkably forms when pressure is exerted in only one direction. Metamorphic rocks may likewise be not-foliated. Quartzite and limestone, shown in table 6, are nonfoliated.

The ii principal types of metamorphism are both related to oestrus within Earth:

1. Regional metamorphism: Changes in enormous quantities of stone 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 loftier temperatures.
2. Contact metamorphism: Changes in a rock that is in contact with magma because of the magma's extreme rut.

Factors that Control Metamorphism

The reason rocks undergo metamorphism is that the minerals in a rock are only 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 by new minerals, minerals that are stable in the new conditions.

Chemical Composition of the Protolith

The blazon of rock undergoes metamorphism is a major cistron in determing what type of metamorphic stone it becomes. In brusque the identify of the protolith plays a big part the identity of the metamorphic stone. A fluid phase may introduce or remove chemical substances into or out of the stone during metamorphism, only in most metamorphic rock, most of the atoms in the protolith are be present in the metamorphic rock after metamorphism; the atoms will likely exist rearranged into new mineral forms within the stone. Therefore, not only does the protolith make up one's mind the initial chemical science of the metamorphic rock, most metamorphic rocks do not change their bulk (overall) chemical compositions very much during metamorphism. The fact that most metamorphic rocks retain nigh of their original atoms means that even if the rock was so thoroughly metamorphosed that information technology no longer looks at all similar the protolith, the stone tin be analyzed in terms of its bulk chemical composition to determine what type of rock the protolith was.

Temperature

Temperature is another major factor of metamorphism. There are ii ways to remember well-nigh how the temperature of a rock tin be increased as a outcome of geologic processes.

If rocks are cached inside the Earth, the deeper they become, the higher the temperatures they experience. This is because temperature inside the Earth increases along what is called the geothermal slope, or geotherm for brusk. Therefore, if rocks are simply buried deep enough plenty sediment, they volition experience temperatures loftier plenty to cause metamorphism. This temperature is about 200ºC (approximately 400ºF).

Tectonic processes are some other way rocks can exist moved deeper along the geotherm. Faulting and folding the rocks of the chaff, tin can move rocks to much greater depth than simple burial tin.

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

Pressure

Pressure is a measure of the stress, the physical force, being applied to the surface of a textile. It is defined as the force per unit area acting on the surface, in a management perpendicular to the surface.

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

If pressure does not apply every bit in all directions, differential stress occurs. In that location are two types of differential stress.

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

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

Differential stress has a major influence on the the appearance of a metamorphic rock. Differential stress can flatten pre-existing grains in the rock, as shown in the diagram below.

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

Fluids

Whatever open space between the mineral grains in a stone, however microscopic, may comprise a fluid phase. Nearly unremarkably, if in that location is a fluid phase in a rock during metamorphism, it will exist a hydrous fluid, consisting of water and things dissolved in the h2o. Less commonly, information technology may exist a carbon dioxide fluid or some other fluid. The presence of a fluid phase is a major factor during metamorphism because it helps determine which metamorphic reactions will occur and how fast they will occur. The fluid phase can as well influence the rate at which mineral crystals deform or alter shape. Nearly of this influence is due to the dissolved ions that pass in and out of the fluid stage. If during metamorphism plenty ions are introduced to or removed from the rock via the fluid to change the bulk chemic composition of the stone, the stone is said to have undergone metasomatism. Yet, well-nigh metamorphic rocks do not undergo sufficient change in their bulk chemistry to be considered metasomatic rocks.

Time

Most metamorphism of rocks takes identify slowly inside the Earth. Regional metamorphism takes place on a timescale of millions of years. Metamorphism normally involves tedious changes to rocks in the solid state, as atoms or ions diffuse out of unstable minerals that are breaking downwards in the given pressure and temperature weather and drift 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 pressure conditions that prevailed during metamorphism. As the pressure and temperature increment, rocks undergo metamorphism at higher metamorphic grade. Rocks irresolute from one type of metamorphic stone to another every bit they encounter higher grades of metamorphism are said to be undergoing prograde metamorphism.

Low-class metamorphism takes place at approximately 200–320 ºC and relatively low pressure. This is non far beyond the conditions in which sediments get lithified into sedimentary rocks, and information technology is common for a low-grade metamorphic rock to wait somewhat like its protolith. Low grade metamorphic rocks tend to characterized by an abundance of hydrous minerals, minerals that contain water inside their crystal construction. Examples of depression form hydrous minerals include clay, serpentine, and chlorite. Nether low grade metamorphism many of the metamorphic minerals will non grow large plenty to be seen without a microscope.

Medium-class metamorphism takes place at approximately at 320–450 ºC and at moderate pressures. Depression form hydrous minerals are replaced past micas such as biotite and muscovite, and not-hydrous minerals such as garnet may abound. Garnet is an instance of a mineral which may form porphyroblasts, metamorphic mineral grains that are larger in size and more equant in shape (nigh the aforementioned diameter in all directions), thus continuing out among the smaller, flatter, or more than elongate minerals.

High-course metamorphism takes identify at temperatures above virtually 450 ºC. Micas tend to break down. New minerals such as hornblende will course, which is stable at higher temperatures. Withal, equally metamorphic grade increases to even higher class, all hydrous minerals, which includes hornblende, may break downwardly and be replaced by other, higher-temperature, not-hydrous minerals such as pyroxene.

Alphabetize Minerals

Index minerals, which are indicators of metamorphic grade. In a given rock blazon, which starts with a item chemical composition, lower-course index minerals are replaced past higher-grade alphabetize minerals in a sequence of chemical reactions that proceeds as the rock undergoes prograde metamorphism. For example, in rocks made of metamorphosed shale, metamorphism may prograde through the following index minerals:

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

Alphabetize minerals are used by geologists to map metamorphic grade in regions of metamorphic stone. 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 alphabetize mineral it contains. By drawing lines around the areas where each type of index mineral occurs, the geologist delineates the zones of dissimilar metamorphic grades in the region. The lines are known every bit isograds.

Types of Metamorphism

Regional Metamorphism

Regional metamorphism occurs where large areas of stone are subjected to large amounts of differential stress for long intervals of time, atmospheric condition typically associated with mountain building. Mount building occurs at subduction zones and at continental collision zones where two plates each begetting continental chaff, converge upon each other.

Most 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 become ductile, which means they are relatively soft even though they are still solid. The folding and deformation of the stone 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 even convoluted shapes. The diagram below shows folds forming during an early stage of regional metamorphism, along with evolution of foliation, in response to normal stress.

The photograph below shows high-grade metamorphic rock that has undergone several stages of foliation development and folding during regional metamorphism, and may even have reached such a high temperature that information technology 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 torso 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 thousand (a few feet) thick, ranging up to contact metamorphic zones over chiliad m (over 3000 anxiety) beyond around larger intrusions that released more oestrus into the adjacent crust. 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 form 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 weather, information technology is sometimes referred to as loftier-temperature, low-pressure level metamorphism. Hornfels, which is a difficult metamorphic stone formed from fine-grained clastic sedimentary rocks, is a common product of contact metamorphism.

Hydrothermal Metamorphism

Hydrothermal metamorphism is the issue of extensive interaction of rock with high-temperature fluids. The difference in limerick between the existing stone 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 sea water. If the fluid introduces substantal amounts of ions into the rock and removes substantial amounts of ions from information technology, the fluid has metasomatized the stone—inverse its chemical composition.

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

Burial Metamorphism

Burying metamorphism occurs to rocks buried below sediments to depths that exceed the conditions in which sedimentary rocks form. Because rocks undergoing burial metamorphism encounter the uniform stress of lithostatic force per unit area, non differential pressure level, they do not develop foliation. Burial metamorphism is the lowest course of metamorphism. The primary blazon of mineral that unremarkably grows during burial metamorphism is zeolite, a grouping of low-density silicate minerals. Information technology usually requires a strong microscope see the small grains of zeolite minerals that form during burial metamorphism.

Subduction Zone Metamorphism

During subduction, a tectonic plate, consisting of oceanic crust and lithospheric mantle, is recycled back into the deeper mantle. In about subduction zones the subducting plate is relatively cold compared with the high temperature information technology had when starting time formed at a mid-ocean spreading ridge. Subduction takes the rocks to great depth in the Globe relatively quickly. This produces a characteristic blazon of metamorphism, sometimes called high-pressure, low-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 loftier-P, low-T weather create a distinctive set of metamorphic minerals including a blazon of amphibole, chosen glaucophane, that has a blue colour. Blueschist is the proper name given to this type of metamorphic rock. Blueschist is mostly interpreted as having been produced within a subduction zone, even if the plate boundaries have subsequently shifted and that location is no longer at a subduction zone.

Metamorphic Facies

Much every bit the minerals and textures of sedimentary rocks tin can exist used equally windows to run across into the environment in which the sediments were deposited on the Earth's surface, the minerals and textures of metamorphic rocks provide windows through which nosotros view the conditions of pressure level, temperature, fluids, and stress that occurred within the Earth during metamorphism. The pressure and temperature conditions nether which specific types of metamorphic rocks course has been determined past a combination labratory experiments, physics-based theoretical calculations, along with evidence in the textures of the rocks and their field relations as recorded on geologic maps. The cognition of temperatures and pressures at which particular types of metamorphic rocks course led to the concept of metamorphic facies. Each metamorphic facies is represented by a specific type of metamorphic rock that forms under a specific pressure and temperature conditions.

Even 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 type of stone that will class in those conditions. For example, if the protolith is basalt, it will 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 green, will form instead. If it tin exist determined that a muscovite-biotite schist formed at around 350ºC temperature and 400 MPa pressure, it tin can exist stated that the rock formed in the greenschist facies, even though the stone is non itself a greenschist.

The diagram below shows metamorphic facies in terms of pressure and temperature condiditons inside the World. Globe's surface conditions are well-nigh the top left corner of the graph at about 15ºC which is the average temperature at Globe's surface and 0.1 MPa (megapascals), which is near the average atmospheric pressure level on the Globe'south surface. But as atmospheric pressure level comes from the weight of all the air higher up a indicate on the Earth's surface, pressure level inside the Earth comes from the weight of all the rock above a given depth. Rocks are much denser than air and MPa is the unit most normally uses to limited pressures inside the Earth. 1 MPa equals nearly x atmospheres. A pressure of k MPa corresponds to a depth of most 35 km within the Earth. Although force per unit area inside the World is determined by the depth, temperature depends on more than depth. Temperature depends on the heat menses, which varies from location to location. The mode temperature changes with depth within the Earth is called the geothermal gradient, geotherm for short. In the diagram beneath, 3 different geotherms are marked with dashed lines. The three geotherms correspond different geological settings in the Earth.

High-pressure level, depression-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 weather condition.

Loftier-temperature, depression-pressure geotherms occur in the vicinity of igneous intrusions in the shallow chaff, underlying a volcanically active surface area. Rocks that have their pressure and temperature weather increased along such a geotherm volition metamorphose in the hornfels facies and, if it gets hot enough, in the granulite facies.

Blueschist facies and hornfels facies are associated with unusual geothermal gradients. The most common atmospheric condition in the Earth are plant forth geotherms between those two extremes. Well-nigh regional metamorphic rocks are formed in atmospheric condition within this range of geothermal gradients, passing through the greenschist facies to the amphibolites facies. At the maximum pressures and temperatures the rocks may encounter within the Earth in this range of geotherms, they volition enter either the granulite or eclogite facies. Regionally metamorphosed rocks that comprise 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. Nearly foliated metamorphic rocks originate from regional metamorphism. Some unfoliated metamorphic rocks, such every bit hornfels, originate only by contact metamorphism, but others can originate either by contact metamorphism or by regional metamorphism. Quartz and marble are prime examples of unfoliated that can be produced by either regional or contact metamorphism. Both stone types consist of metamorphic minerals that practice non accept apartment or elongate shapes and thus cannot become layered fifty-fifty 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 form in outcrops as well as how those outcrops are related to other types of rock with which they are in contact. Field evidence is oft required to know for sure whether rocks are products of regional metamorphism, contact metamorphism, or another type of metamorphism. If only looking at rock samples in a laboratory, ane can be certain of the blazon of metamorphism that produced a foliated metamorphic rock such every bit schist or gneiss, or a hornfels, which is unfoliated, only ane cannot be certain 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. Even so, a more than complete proper noun of each detail blazon of foliated metamorphic rock includes the main minerals that the rock comprises, such as biotite-garnet schist rather than only schist.

• slate—slates grade at low metamorphic grade by the growth of fine-grained chlorite and clay minerals. The preferred orientation of these canvass silicates causes the stone 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 as the base of pool tables, beneath a layer of rubber and felt. Roof tiles are also sometimes made of slate.
• phyllite—phyllite is a low-medium grade regional metamorphic rock in which the clay minerals and chlorite have been at to the lowest degree partly replaced past 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 accept produced a prepare of folds in the stone, making the foliation surfaces wavy or irregular, in contrast to the frequently perfectly flat surfaces of slaty cleavage.
• schist—the size of mineral crystals tends to grow 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 sail silicates, ordinarily 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 than simply micas among its minerals, such equally quartz, feldspars, and garnet.
• amphibolite—a poorly foliated to unfoliated mafic metamorphic stone, usually consisting largely of the common black amphibole known as hornblende, plus plagioclase, plus or minus biotite and peradventure other minerals; it usually does not contain any quartz. Amphibolite forms at medium-high metamorphic grades. Amphibolite is also listed below in the section on unfoliated metamorphic rocks.
• gneiss—like the discussion schist, the give-and-take gneiss is originated from the German language; it is pronounced "nice." Equally metamorphic form proceed to increase, sheet silicates become unstable and dark minerals such as hornblende or pyroxene start to grow. The dark-colored minerals tend to form split bands or stripes in the rock, giving it a gneissic foliation of dark and light streaks. Gneiss is a high-grade metamorphic rock. Many types of gneiss wait somewhat like granite, except that the gneiss has night and low-cal stripes whereas in granite randomly oriented and distributed minerals with no stripes or layers.
• migmatite—a combination of loftier-grade regional metamorphic rock – usually gneiss or schist – and granitic igneous rock. The granitic rock in migmatite probably originated from partial melting of some of the metamorphic rock, though in some migmatites the granite may take intruded the rock from deeper in the chaff. In migmatite you can see metamorphic stone that has reached the limits of metamorphism and begun transitioning into the igneous phase of the rock cycle by melting to form magma.

Names of unlike styles of foliation come from the common 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 abound nether differential stress, or considering the minerals that grew during metamorphism are not minerals that have elongate or apartment 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 heat from the nearby magma "bakes" the sedimentary rocks and recrystallizes the minerals in them into a new texture that no longer breaks easily along the original sedimentary bedding planes. Depending on the composition of the stone and the temperature reached, minerals indicative of high metamorphic class such every bit pyroxene may occur in some hornfels, though many hornfels have minerals indicating medium form metamorphism.
• amphibolite—amphibolites are dark-colored rocks with amphibole, usually the common blackness amphibole known equally 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-loftier grades of metamorphism from basalt or gabbro.
• quartzite—quartzite is a metamorphic rock made almost entirely of quartz, for which the protolith was quartz arenite. Considering quartz is stable over a broad range of force per unit area and temperature, piddling or no new minerals class in quartzite during metamorphism. Instead, the quartz grains recrystallize into a denser, harder rock than the original sandstone. If struck by a rock hammer, quartzite will commonly break correct through the quartz grains, rather than effectually them equally when quartz arenite is broken.
• marble—marble is a metamorphic rock made up about entirely of either calcite or dolomite, for which the protolith was either limestone or dolostone, respectively. Marbles may have bands of unlike colors which were plain-featured into convoluted folds while the stone was ductile. Such marble is oft used equally decorative stone in buildings. Some marble, which is considered better quality rock for etching into statues, lacks color bands.

Tabular array one. Mutual Metamorphic Rocks and Their Parent Rock
Movie	Rock Proper name	Blazon of Metamorphic Stone	Comments
	Slate	Foliated	Metamorphism of shale
	Phyllite	Foliated	Metamorphism of slate, simply under greater estrus and pressure than slate
	Schist	Foliated	Ofttimes derived from metamorphism of claystone or shale; metamorphosed under more oestrus and pressure than phyllite
	Gneiss	Foliated	Metamorphism of various unlike rocks, under farthermost atmospheric condition of heat and pressure level
	Hornfels	Non-foliated	Contact metamorphism of diverse different stone types
	Quartzite	Not-foliated	Metamorphism of sandstone
	Marble	Not-foliated	Metamorphism of limestone
	Metaconglomerate	Non-foliated	Metamorphism of conglomerate

Metamorphic Rock Classification

Foliated Metamorphic Rocks
Crystal Size	Mineralogy	Protolith	Metamorphism	Stone Name
very fine	clay minerals	shale	low grade regional	slate
fine	clay minerals, biotite, muscovite	shale	low grade regional	phyllite
medium to coarse	biotite, muscovite, quartz, garnet, plagioclase	shale, basalt	medium grade regional	schist
medium to coarse	amphibole, plagioclase, biotite	basalt	medium class regional	amphibolite (Note: may be unfoliated)
medium to coarse	plagioclase, orthoclase, quartz, biotite, amphibole, pyroxene	basalt, granite, shale	high grade 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

Note that not all minerals listed in the mineralogy column will exist present in every rock of that type and that some rocks may have minerals not listed here.

Uses of Metamorphic Rocks

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

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

Quartzite is very hard and is often crushed and used in building railroad tracks (come across effigy 4). Schist and slate are sometimes used as building and landscape materials. Graphite, the "lead" in pencils, is a mineral unremarkably found in metamorphic rocks.

Figure iv. Crushed quartzite is sometimes placed under railroad tracks because information technology is very hard and durable.

Identifying Metamorphic Rocks

This video discusses how to identify a metamorphic rocks:

Check Your Understanding

Answer the question(southward) below to see how well you understand the topics covered in the previous department. This short quiz doesnot count toward your class in the course, and you lot tin retake it an unlimited number of times.

Use this quiz to check your understanding and decide whether to (i) report the previous section further or (2) movement on to the adjacent section.

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

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