Quartzite, a form of metamorphic rock, from the Museum of Geology at University of Tartu collection.

Metamorphic rock is the result of the transformation of a pre-existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure (temperatures greater than 150 to 200 °C and pressures of 1500 bars^[1]) causing profound physical and/or chemical change. The protolith may be sedimentary rock, igneous rock or another older metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and are classified by texture and by chemical and mineral assemblage (metamorphic facies). They may be formed simply by being deep beneath the Earth's surface, subjected to high temperatures and the great pressure of the rock layers above. They can be formed by tectonic processes such as continental collisions which cause horizontal pressure, friction and distortion. They are also formed when rock is heated up by the intrusion of hot molten rock called magma from the Earth's interior. Image File history File links Quartzite. ... Image File history File links Quartzite. ... Quartzite Quartzite (from German Quarzit[1]) is a hard, metamorphic rock which was originally sandstone. ... The University of Tartu (Estonian: ; Russian: ; German: ) is a classical university in the city of Tartu, Estonia. ... Rock redirects here. ... Metamorphism can be defined as the solid state recrystallisation of pre-existing rocks due to changes in heat and/or pressure and/or introduction of fluids i. ... Two types of sedimentary rock: limey shale overlaid by limestone. ... Igneous rocks (etymology from Latin ignis, fire) are rocks formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... This article is about Earth as a planet. ... World geologic provinces (USGS) Oceanic crust  0-20 Ma  20-65 Ma  >65 Ma Geologic province  Shield  Platform  Orogen  Basin  Large igneous province  Extended crust In geology, a crust is the outermost solid shell of a planet or moon. ... A chemical substance is any material substance used in or obtained by a process in chemistry: A chemical compound is a substance consisting of two or more chemical elements that are chemically combined in fixed proportions. ... For other uses, see Mineral (disambiguation). ... The tectonic plates of the world were mapped in the second half of the 20th century. ... Pluton redirects here. ... Magma is molten rock located beneath the surface of the Earth (or any other terrestrial planet), and which often collects in a magma chamber. ...

The study of metamorphic rocks (now exposed at the Earth's surface following erosion and uplift) provides us with very valuable information about the temperatures and pressures that occur at great depths within the Earth's crust.

Some examples of metamorphic rocks are gneiss, slate, marble and schist. Gneiss Gneiss (IPA: ) is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from preexisting formations that were originally either igneous or sedimentary rocks, which most commonly forms on ancient seabeds. ... For other uses, see Slate (disambiguation). ... For other uses, see Marble (disambiguation). ... Schist The schists form a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. ...

Metamorphic minerals

Metamorphic minerals are those that form only at the high temperatures and pressures associated with the process of metamorphism. These minerals, known as index minerals, include sillimanite, kyanite, staurolite, andalusite, and some garnet. The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... Sillimanite: Biotite gneiss (Mesozoic and Paleozoic) Sillimanite is an alumino-sillicate mineral with the chemical formula Al2SiO5. ... Kyanite, whose name derives from the Greek, kyanos, meaning blue, is a typically blue silicate mineral, commonly found in aluminium-rich metamorphic pegmatites and/or sedimentary rock. ... Staurolite Staurolite is a red brown to black mostly opaque nesosilicate mineral with a white streak. ... Andalusite-cordierite schist (Large brown crystals are Andalusite Andalusite is an aluminium nesosilicate mineral with the chemical formula Al2SiO5. ... Garnet is a group of minerals that have been used since the Bronze Age as gemstones and abrasives. ...

Other minerals, such as olivines, pyroxenes, amphiboles, micas, feldspars, and quartz, may be found in metamorphic rocks, but are not necessarily the result of the process of metamorphism. These minerals formed during the crystallization of igneous rocks. They are stable at high temperatures and pressures and may remain chemically unchanged during the metamorphic process. However, all minerals are stable only within certain limits, and the presence of some minerals in metamorphic rocks indicates the approximate temperatures and pressures at which they were formed. The mineral olivine (also called chrysolite and, when gem-quality, peridot) is a magnesium iron silicate with the formula (Mg,Fe)2SiO4. ... Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... For the logical fallacy, see Amphibology. ... Rock with mica Mica sheet Mica flakes The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. ... This article does not cite any references or sources. ... For other uses, see Quartz (disambiguation). ... Frost crystallization on a shrub. ...

The change in the particle size of the rock during the process of metamorphism is called recrystallization. For instance, the small calcite crystals in the sedimentary rock limestone change into larger crystals in the metamorphic rock marble, or in metamorphosed sandstone, recrystallisation of the original quartz sand grains results in very compact quartzite, in which the often larger quartz crystals are interlocked. Both high temperatures and pressures contribute to recrystallization. High temperatures allow the atoms and ions in solid crystals to migrate, thus reorganizing the crystals, while high pressures cause solution of the crystals within the rock at their point of contact. Insulin crystals Recrystallization is an essentially physical process that has meanings in chemistry, metallurgy and geology. ... Doubly refracting Calcite from Iceberg claim, Dixon, New Mexico. ... For other uses, see Limestone (disambiguation). ... For other uses, see Marble (disambiguation). ... Properties For other meanings of Atom, see Atom (disambiguation). ... This article is about the electrically charged particle. ...

Foliation

Metamorphic rock foliated in two perpendicular directions, found in Mosaic Canyon of Death Valley National Park

The layering within metamorphic rocks is called foliation (derived from the Latin word folia, meaning "leaves"), and it occurs when a the rock is being compressed from one direction to a recrystallizing rock. This causes the platy or elongated crystals of minerals, such as mica and chlorite, to grow with their long axes perpendicular to the direction of the force. This results in a banded, or foliated, rock, with the bands showing the colors of the minerals that formed them. Image File history File linksMetadata Size of this preview: 800 × 531 pixel Image in higher resolution (2048 × 1360 pixel, file size: 2. ... Image File history File linksMetadata Size of this preview: 800 × 531 pixel Image in higher resolution (2048 × 1360 pixel, file size: 2. ... Death Valley National Park is a mostly arid United States National Park located east of the Sierra Nevada mountain range in southern Inyo County and northern San Bernardino County in California with a small extension into southwestern Nye County and extreme southern Esmeralda County in Nevada. ... Foliation is any penetrative planar fabric present in rocks. ... For other uses, see Latin (disambiguation). ... Rock with mica Mica sheet Mica flakes The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. ... Chlorite is a group of phyllosilicate minerals often classified as clays. ...

Textures are separated into foliated and non-foliated categories. Foliated rock is a product of differential stress that deforms the rock in one plane, sometimes creating a plane of cleavage: for example, slate is a foliated metamorphic rock, originating from shale. Non-foliated rock does not have planar patterns of stress. Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite planes, creating smooth surfaces, of which there are several named types: Basal cleavage: cleavage parallel to the base of a crystal, or to the plane of the lateral axes. ... For other uses, see Slate (disambiguation). ... Shale Shale is a fine-grained sedimentary rock whose original constituents were clays or muds. ...

Rocks that were subjected to uniform pressure from all sides, or those which lack minerals with distinctive growth habits, will not be foliated. Slate is an example of a very fine-grained, foliated metamorphic rock, while phyllite is coarse, schist coarser, and gneiss very coarse-grained. Marble is generally not foliated, which allows its use as a material for sculpture and architecture. Phyllite Phyllite is a type of foliated metamorphic rock primarily composed of quartz, sericite mica, and chlorite; the rock represents a gradiation in the degree of metamorphism between slate and mica schist. ... Schist The schists form a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. ... Gneiss Gneiss (IPA: ) is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from preexisting formations that were originally either igneous or sedimentary rocks, which most commonly forms on ancient seabeds. ... Sculptor redirects here. ... This article is about building architecture. ...

Another important mechanism of metamorphism is that of chemical reactions that occur between minerals without them melting. In the process atoms are exchanged between the minerals, and thus new minerals are formed. Many complex high-temperature reactions may take place, and each mineral assemblage produced provides us with a clue as to the temperatures and pressures at the time of metamorphism.

Metasomatism is the drastic change in the bulk chemical composition of a rock that often occurs during the processes of metamorphism. It is due to the introduction of chemicals from other surrounding rocks. Water may transport these chemicals rapidly over great distances. Because of the role played by water, metamorphic rocks generally contain many elements that were absent from the original rock, and lack some which were originally present. Still, the introduction of new chemicals is not necessary for recrystallization to occur. Metasomatism is the chemical alteration of a rock by hydrothermal and other fluids. ...

Types of metamorphism

Contact metamorphism

Contact metamorphism is the name given to the changes that take place when magma is injected into the surrounding solid rock (country rock). The changes that occur are greatest wherever the magma comes into contact with the rock because the temperatures are highest at this boundary and decrease with distance from it. Around the igneous rock that forms from the cooling magma is a metamorphosed zone called a contact metamorphism aureole. Aureoles may show all degrees of metamorphism from the contact area to unmetamorphosed (unchanged) country rock some distance away. The formation of important ore minerals may occur by the process of metasomatism at or near the contact zone. For other uses, see Ore (disambiguation). ... Metasomatism is the chemical alteration of a rock by hydrothermal and other fluids. ...

When a rock is contact altered by an igneous intrusion it very frequently becomes more indurated, and more coarsely crystalline. Many altered rocks of this type were formerly called hornstones, and the term hornfels is often used by geologists to signify those fine grained, compact, non-foliated products of contact metamorphism. A shale may become a dark argillaceous hornfels, full of tiny plates of brownish biotite; a marl or impure limestone may change to a grey, yellow or greenish lime-silicate-honrfels or siliceous marble, tough and splintery, with abundant augite, garnet, wollastonite and other minerals in which calcite is an important component. A diabase or andesite may become a diabase hornfels or andesite hornfels with development of new hornblende and biotite and a partial recrystallization of the original feldspar. Chert or flint may become a finely crystalline quartz rock; sandstones lose their clastic structure and are converted into a mosaic of small close-fitting grains of quartz in a metamorphic rock called quartzite. Hornfels (German, meaning hornstone) is the group designation for a series of contact metamorphic rocks that have been baked and indurated by the heat of intrusive granitic masses and have been rendered massive, hard, splintery, and in some cases exceedingly tough and durable. ... Shale Shale is a fine-grained sedimentary rock whose original constituents were clays or muds. ... Argillaceous minerals are minerals containing substantial amounts of clay-like components (Greek: ἄργιλλος = clay). ... A Biotite slice Biotite is a common phyllosilicate mineral that contains potassium, magnesium, iron and aluminium. ... Marls are calcium carbonate or lime rich muds or mudstones which contain variable amounts of clays and calcite or aragonite. ... For other uses, see Limestone (disambiguation). ... For other uses, see Marble (disambiguation). ... Augite is a single chain inosilicate mineral described chemically as (Ca,Mg,Fe)SiO3 or calcium magnesium iron silicate. ... Garnet is a group of minerals that have been used since the Bronze Age as gemstones and abrasives. ... Wollastonite is a calcium inosilicate mineral (CaSiO3) that may contain small amounts of iron, magnesium, and manganese substituting for calcium. ... Doubly refracting Calcite from Iceberg claim, Dixon, New Mexico. ... It has been suggested that this article or section be merged with Dolerite. ... A sample of andesite (dark groundmass) with amygdaloidal vesicules filled with zeolite. ... Chert Chert (IPA: ) is a fine-grained silica-rich cryptocrystalline sedimentary rock that may contain small fossils. ... This article is about the sedimentary rock. ... Red sandstone interior of Lower Antelope Canyon, Arizona, worn smooth due to erosion by flash flooding over millions of years Sandstone is a sedimentary rock composed mainly of sand-size mineral or rock grains. ... In geology, the term clastic refers to sediments formed from fragments of pre-existing rock. ... Quartzite Quartzite (from German Quarzit[1]) is a hard, metamorphic rock which was originally sandstone. ...

If the rock was originally banded or foliated (as, for example, a laminated sandstone or a foliated calc-schist) this character may not be obliterated, and a banded hornfels is the product; fossils even may have their shapes preserved, though entirely recrystallized, and in many contact-altered lavas the vesicles are still visible, though their contents have usually entered into new combinations to form minerals which were not originally present. The minute structures, however, disappear, often completely, if the thermal alteration is very profound; thus small grains of quartz in a shale are lost or blend with the surrounding particles of clay, and the fine ground-mass of lavas is entirely reconstructed. Foliation is any penetrative planar fabric present in rocks. ... Schist The schists form a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. ... For other uses, see Fossil (disambiguation). ... Look up lava, Aa, pahoehoe in Wiktionary, the free dictionary. ... In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ...

By recrystallization in this manner peculiar rocks of very distinct types are often produced. Thus shales may pass into cordierite rocks, or may show large crystals of andalusite (and chiastolite), staurolite, garnet, kyanite and sillimanite, all derived from the aluminous content of the original shale. A considerable amount of mica (both muscovite and biotite) is often simultaneously formed, and the resulting product has a close resemblance to many kinds of schist. Limestones, if pure, are often turned into coarsely crystalline marbles; but if there was an admixture of clay or sand in the original rock such minerals as garnet, epidote, idocrase, wollastonite, will be present. Sandstones when greatly heated may change into coarse quartzites composed of large clear grains of quartz. These more intense stages of alteration are not so commonly seen in igneous rocks, because their minerals, being formed at high temperatures, are not so easily transformed or recrystallized. Cordierite is a magnesium iron aluminum cyclosilicate with associated water. ... Andalusite-cordierite schist (Large brown crystals are Andalusite Andalusite is an aluminium nesosilicate mineral with the chemical formula Al2SiO5. ... The mineral chiastolite is a variety of Andalusite with the chemical composition Al2OSiO4. ... Staurolite Staurolite is a red brown to black mostly opaque nesosilicate mineral with a white streak. ... Garnet is a group of minerals that have been used since the Bronze Age as gemstones and abrasives. ... Kyanite, whose name derives from the Greek, kyanos, meaning blue, is a typically blue silicate mineral, commonly found in aluminium-rich metamorphic pegmatites and/or sedimentary rock. ... Sillimanite: Biotite gneiss (Mesozoic and Paleozoic) Sillimanite is an alumino-sillicate mineral with the chemical formula Al2SiO5. ... Rock with mica Mica sheet Mica flakes The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. ... Epidote from Slovakia Epidote is a calcium aluminium iron sorosilicate mineral, Ca2(Al, Fe)3(SiO4)3(OH), crystallizing in the monoclinic system. ... Vesuvianite is a green, brown, yellow, or blue metamorphic silicate mineral, Ca10Mg2Al4(SiO4)5(Si2O7)2(OH)4. ...

In a few cases rocks are fused and in the dark glassy product minute crystals of spinel, sillimanite and cordierite may separate out. Shales are occasionally thus altered by basalt dikes, and feldspathic sandstones may be completely vitrified. Similar changes may be induced in shales by the burning of coal seams or even by an ordinary furnace. The spinels are any of a class of minerals which crystallize in the isometric system with an octahedral habit. ... Cordierite is a magnesium iron aluminum cyclosilicate with associated water. ... A dike in geology refers to a tabular intrusive igneous body. ... Coal Example chemical structure of coal Coal (pronounced ) is a fossil fuel formed in swamp ecosystems where plant remains were saved by water and mud from oxidization and biodegradation. ...

There is also a tendency for metasomatism between the igneous magma and sedimentary country rock, whereby the chemicals in each are exchanged or introduced into the other. Granites may absorb fragments of shale or pieces of basalt. In that case hybrid rocks called skarn arise which have not the characters of normal igneous or sedimentary rocks. Sometimes an invading granite magma permeates the rocks around, filling their joints and planes of bedding, etc., with threads of quartz and feldspar. This is very exceptional but instances of it are known and it may take place on a large scale.^[2] Metasomatism is the chemical alteration of a rock by hydrothermal and other fluids. ... Skarn: microscopic view under crossed polarizers Skarn is a metamorphic rock that is usually variably colored green or red, occasionally grey, black, brown or white. ...

Regional metamorphism

Regional metamorphism is the name given to changes in great masses of rock over a wide area. Rocks can be metamorphosed simply by being at great depths below the Earth's surface, subjected to high temperatures and the great pressure caused by the immense weight of the rock layers above. Much of the lower continental crust is metamorphic, except for recent igneous intrusions. Horizontal tectonic movements such as the collision of continents create orogenic belts, and cause high temperatures, pressures and deformation in the rocks along these belts. If the metamorphosed rocks are later uplifted and exposed by erosion, they may occur in long belts or other large areas at the surface. The process of metamorphism may have destroyed the original features that could have revealed the rock's previous history. Recrystallization of the rock will destroy the textures and fossils present in sedimentary rocks. Metasomatism will change the original composition. // Orogeny (Greek for mountain generating) is the process of mountain building, and may be studied as a tectonic structural event, as a geographical event and a chronological event, in that orogenic events cause distinctive structural phenomena and related tectonic activity, affect certain regions of rocks and crust and happen within... For morphological image processing operations, see Erosion (morphology). ... Insulin crystals Recrystallization is an essentially physical process that has meanings in chemistry, metallurgy and geology. ... For other uses, see Fossil (disambiguation). ...

Regional metamorphism tends to make the rock more indurated and at the same time to give it a foliated, shistose or gneissic texture, consisting of a planar arrangement of the minerals, so that platy or prismatic minerals like mica and hornblende have their longest axes arranged parallel to one another. For that reason many of these rocks split readily in one direction along mica-bearing zones (schists). In gneisses, minerals also tend to be segregated into bands; thus there are seams of quartz and of mica in a mica schist, very thin, but consisting essentially of one mineral. Along the mineral layers composed of soft or fissile minerals the rocks will split most readily, and the freshly split specimens will appear to be faced or coated with this mineral; for example, a piece of mica schist looked at facewise might be supposed to consist entirely of shining scales of mica. On the edge of the specimens, however, the white folia of granular quartz will be visible. In gneisses these alternating folia are sometimes thicker and less regular than in schists, but most importantly less micaceous; they may be lenticular, dying out rapidly. Gneisses also, as a rule, contain more feldspar than schists do, and they are tougher and less fissile. Contortion or crumbling of the foliation is by no means uncommon, and then the splitting faces are undulose or puckered. Schistosity and gneissic banding (the two main types of foliation) are formed by directed pressure at elevated temperature, and to interstitial movement, or internal flow arranging the mineral particles while they are crystallizing in that directed pressure field. Schist The schists form a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. ... Gneiss Gneiss (IPA: ) is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from preexisting formations that were originally either igneous or sedimentary rocks, which most commonly forms on ancient seabeds. ...

Rocks which were originally sedimentary and rocks which were undoubtedly igneous are converted into schists and gneisses, and if originally of similar composition they may be very difficult to distinguish from one another if the metamorphism has been great. A quartz-porphyry, for example, and a fine feldspathic sandstone, may both the converted into a grey or pink mica-schist.^[2] Quartz-porphyry, in petrology, is the name given to a group of hemi-crystalline acid rocks containing porphyritic crystals of quartz in a more fine-grained matrix which is usually of micro-crystalline or felsitic structure. ...

Metamorphic rock textures

The five basic metamorphic textures with typical rock types are:

• Slaty: slate and phyllite; the foliation is called 'slaty cleavage'
• Schistose: schist; the foliation is called 'schistosity'
• Gneissose: gneiss; the foliation is called 'gneissosity'
• Granoblastic: granulite, some marbles and quartzite
• Hornfelsic: hornfels and skarn

For other uses, see Slate (disambiguation). ... Phyllite Phyllite is a type of foliated metamorphic rock primarily composed of quartz, sericite mica, and chlorite; the rock represents a gradiation in the degree of metamorphism between slate and mica schist. ... Schist The schists form a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. ... Gneiss Gneiss (IPA: ) is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from preexisting formations that were originally either igneous or sedimentary rocks, which most commonly forms on ancient seabeds. ... Modern petrology defnes a granulite sensuo stricto as a coarse grained, high-grade metamorphic rock composed primarily of pyroxene, plagioclase feldspar and accessory garnet, oxide and amphibole. ... For other uses, see Marble (disambiguation). ... Quartzite Quartzite (from German Quarzit[1]) is a hard, metamorphic rock which was originally sandstone. ... Hornfels (German, meaning hornstone) is the group designation for a series of contact metamorphic rocks that have been baked and indurated by the heat of intrusive granitic masses and have been rendered massive, hard, splintery, and in some cases exceedingly tough and durable. ... Skarn: microscopic view under crossed polarizers Skarn is a metamorphic rock that is usually variably colored green or red, occasionally grey, black, brown or white. ...

See also

• List of minerals
• List of rock types
• List of rock textures
• Blueschist

Gem animals. ... This page is intended as a list of all rock types. ... This page is intended to be a list of rock textural and morphological terms. ... Blueschist is a rock that forms by the metamorphism of sodium-rich basic rocks at high pressures and low temperatures, approximately corresponding to a depth of 15 to 30 kilometers and 200 to 400 degrees Celsius (cool by metamorphic standards). ...

References

1. ^ Blatt, Harvey and Robert J. Tracy, Petrology, W.H.Freeman, 2nd ed., 1996, p.355 ISBN 0-7167-2438-3
2. ^ ^{a b} This article incorporates text from the Encyclopædia Britannica Eleventh Edition article "Petrology", a publication now in the public domain.

Encyclopædia Britannica, the eleventh edition The Encyclopædia Britannica Eleventh Edition (1910–1911) is perhaps the most famous edition of the Encyclopædia Britannica. ... The public domain comprises the body of all creative works and other knowledge—writing, artwork, music, science, inventions, and others—in which no person or organization has any proprietary interest. ...

External links

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Metamorphic rock

• Metamorphic textures - Middle East Technical University
• Metamorphism - U. of Alabama
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• Contact metamorphism example