Metamorphic rock

Quartzite, a form of metamorphic rock, from the Museum of Geology at University of Tartu collection. Quartzite (from German Quarzit) not to be confused with the Mineral Quartz, is a hard Metamorphic rock which was originally The University of Tartu (Tartu Ülikool Тартуский университет Universität Dorpat is a classical University in the city of Tartu, Estonia

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 ". In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere 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 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. Sedimentary rock is one of the three main rock types (the others being igneous and Metamorphic rock) Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten 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). EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 In Geology, a crust is the outermost solid shell of a planet or moon A chemical substance is a Material with a definite chemical composition. A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific Historic definition The name facies was first used for specific Sedimentary environments in Sedimentary rocks by Swiss geologist Amanz 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. Plate tectonics (from Greek τέκτων tektōn "builder" or "mason" describes the large scale motions of Earth 's Lithosphere They are also formed when rock is heated up by the intrusion of hot molten rock called magma from the Earth's interior. In Geology, an intrusion is a body of Igneous rock that has Crystallized from molten Magma below the surface of the Earth. Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet

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 (ˈnaɪs is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from preexisting formations that were originally Slate is a fine-grained foliated homogeneous, Metamorphic rock derived from an original Shale -type Sedimentary rock composed of Clay Marble is a nonfoliated Metamorphic rock resulting from the Metamorphism of Limestone, composed mostly of Calcite (a crystalline form of The schists form a group of medium-grade Metamorphic rocks chiefly notable for the preponderance of lamellar Minerals such as Micas chlorite

1 Metamorphic minerals
2 Foliation
3 Types of metamorphism
- 3.1 Contact metamorphism
- 3.2 Regional metamorphism
4 Metamorphic rock textures
5 See also
6 References
7 External links

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. An index mineral is used in geology to determine the degree of Metamorphism a rock has experienced Sillimanite also called Bucholzite is an alumino-silicate Mineral with the Chemical formula Al2SiO5 Kyanite, whose name derives from the Greek word kyanos, meaning blue is a typically blue Silicate Mineral, commonly found in Aluminium -rich Staurolite is a red brown to black mostly opaque nesosilicate Mineral with a white streak Andalusite is an Aluminium nesosilicate Mineral with the chemical formula Al2SiO5 The garnet group includes 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. The Mineral olivine (when gem-quality also called Peridot) is a Magnesium Iron silicate with the formula ( Mg The pyroxenes are a group of important rock-forming Silicate minerals found in many Igneous and metamorphic rocks. Amphibole (pronounced amfi-bowl defines an important group of generally dark-colored rock-forming inosilicate Minerals composed of double chain SiO4 The word "mica" is thought to be derived from the Latin word la micare, "glitteren" in reference to the brilliant appearance of this mineral (especially Feldspar is the name of a group of rock-forming Minerals which make up as much as 60% of the Earth 's crust. Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in These minerals formed during the crystallization of igneous rocks. Crystallization is the (natural or artificial process of formation of solid Crystals precipitating from a homogeneous --> identical Solution 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 change in the particle size of the rock during the process of metamorphism is called recrystallization. Recrystallization (see also Crystallization) is a physical process that has meanings in Chemistry, Metallurgy and Geology. 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. Calcite is a carbonate mineral and the most stable polymorph of Calcium carbonate ( Ca[[carbon C]] O 3 Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3 Marble is a nonfoliated Metamorphic rock resulting from the Metamorphism of Limestone, composed mostly of Calcite (a crystalline form of 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. History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge

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 rock is being compressed from one direction to a recrystallizing rock. Death Valley National Park is a mostly Arid United States National Park located east of the Sierra Nevada mountain range in southern Inyo County Foliation is any penetrative planar fabric present in rocks. Foliation is common to rocks affected by regional metamorphic compression typical of orogenic Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. 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. The word "mica" is thought to be derived from the Latin word la micare, "glitteren" in reference to the brilliant appearance of this mineral (especially The chlorites are a group of phyllosilicate Minerals Chlorites can be described by the following four endmembers based on their chemistry via substitution This results in a banded, or foliated, rock, with the bands showing the colors of the minerals that formed them.

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. Cleavage, in Mineralogy, is the tendency of crystalline materials to split along definite planes creating smooth surfaces of which there are several named types Slate is a fine-grained foliated homogeneous, Metamorphic rock derived from an original Shale -type Sedimentary rock composed of Clay Shale (also called mudstone) is a fine-grained Sedimentary rock whose original constituents were Clay minerals or Muds It is characterized by Non-foliated rock does not have planar patterns of stress.

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. Phyllite is a type of foliated Metamorphic rock primarily composed of Quartz, Sericite Mica, and chlorite; the rock represents The schists form a group of medium-grade Metamorphic rocks chiefly notable for the preponderance of lamellar Minerals such as Micas chlorite Gneiss (ˈnaɪs is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from preexisting formations that were originally Marble is generally not foliated, which allows its use as a material for sculpture and 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.

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. An ore is a volume of rock containing components or Minerals in a mode of occurrence that renders it valuable for mining 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. Hornfels ( German, meaning "hornstone" is the group designation for a series of contact metamorphic rocks that have been baked and indurated by the heat 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. Shale (also called mudstone) is a fine-grained Sedimentary rock whose original constituents were Clay minerals or Muds It is characterized by Argillaceous minerals appear silvery upon optical reflection and are Minerals containing substantial amounts of Clay -like components (ἄργιλλος = clay Biotite is a common phyllosilicate Mineral within the Mica group with the approximate chemical formula K(Mg Fe3AlSi3O10(F Marl or Marlstone is a Calcium carbonate or lime -rich mud or Mudstone which contains variable amounts of Clays and Aragonite Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3 Marble is a nonfoliated Metamorphic rock resulting from the Metamorphism of Limestone, composed mostly of Calcite (a crystalline form of Augite is a single chain inosilicate Mineral described chemically as (CaMgFeSiO3 or Calcium Magnesium Iron The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives Calcite is a carbonate mineral and the most stable polymorph of Calcium carbonate ( Ca[[carbon C]] O 3 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. Diabase (ˈdaɪəbeɪs or Dolerite is a Mafic, Holocrystalline, Igneous rock equivalent to Volcanic Basalt or plutonic For the extinct cephalopod genus see Andesites. Andesite (ˈændəsaɪt is an igneous, Volcanic rock, of intermediate 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. Chert (ˈtʃɝt is a fine-grained Silica -rich Microcrystalline, Cryptocrystalline or Microfibrous Sedimentary rock that may contain Flint (or flintstone) is a hard sedimentary Cryptocrystalline form of the Mineral Quartz, categorized as a variety of Chert Sandstone is a Sedimentary rock composed mainly of Sand -size Mineral or rock grains. Clastic rocks are composed of fragments or clasts, of pre-existing rock. Quartzite (from German Quarzit) not to be confused with the Mineral Quartz, is a hard Metamorphic rock which was originally

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. Foliation is any penetrative planar fabric present in rocks. Foliation is common to rocks affected by regional metamorphic compression typical of orogenic The schists form a group of medium-grade Metamorphic rocks chiefly notable for the preponderance of lamellar Minerals such as Micas chlorite FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. Lava is molten rock expelled by a Volcano during an eruption When first expelled from a volcanic vent it is a Liquid at Temperatures 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.

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. Cordierite ( Mineralogy) or iolite ( Gemology) is a Magnesium Iron Aluminium cyclosilicate. Andalusite is an Aluminium nesosilicate Mineral with the chemical formula Al2SiO5 The Mineral chiastolite is a variety of Andalusite with the chemical composition Al2SiO5 Staurolite is a red brown to black mostly opaque nesosilicate Mineral with a white streak The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives Kyanite, whose name derives from the Greek word kyanos, meaning blue is a typically blue Silicate Mineral, commonly found in Aluminium -rich Sillimanite also called Bucholzite is an alumino-silicate Mineral with the Chemical formula Al2SiO5 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. The word "mica" is thought to be derived from the Latin word la micare, "glitteren" in reference to the brilliant appearance of this mineral (especially 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. Epidote is a Calcium Aluminium Iron sorosilicate Mineral, Ca2Al2(Fe3+Al(SiO4(Si2O7O(OH Vesuvianite, also known as idocrase is a green brown yellow or blue silicate mineral. 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.

In a few cases rocks are fused and in the dark glassy product minute crystals of spinel, sillimanite and cordierite may separate out. The spinels are any of a class of Minerals of general formulation XY2 O 4 which Crystallize in the cubic (isometric Cordierite ( Mineralogy) or iolite ( Gemology) is a Magnesium Iron Aluminium cyclosilicate. Shales are occasionally thus altered by basalt dikes, and feldspathic sandstones may be completely vitrified. A dike or dyke in Geology is a type of Sheet intrusion referring to any geologic body that cuts Discordantly ' across planar Similar changes may be induced in shales by the burning of coal seams or even by an ordinary furnace.

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. Metasomatism is the chemical alteration of a rock by Hydrothermal and other fluids 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. Skarn is a Metamorphic rock that is usually variably colored green or red occasionally grey black brown or white 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]

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. Orogeny (Greek for "mountain generating" is the process of natural Mountain building and may be studied as a tectonic structural event as a geographical event and If the metamorphosed rocks are later uplifted and exposed by erosion, they may occur in long belts or other large areas at the surface. Erosion is the carrying away or displacement of solids ( Sediment, Soil, rock and other particles usually by the agents of currents such as wind 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. Recrystallization (see also Crystallization) is a physical process that has meanings in Chemistry, Metallurgy and Geology. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. Metasomatism will change the original composition.

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). The schists form a group of medium-grade Metamorphic rocks chiefly notable for the preponderance of lamellar Minerals such as Micas chlorite 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. Gneiss (ˈnaɪs is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from preexisting formations that were originally 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.

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. Quartz-porphyry, in Petrology, is the name given to a group of hemi- Crystalline Acid rocks containing Porphyritic crystals of ^[2]