grains, and such textures as shatter cones in the impacted rock. { metamorphism usually results in forming metamorphic rocks that are strongly foliated, such return "" + Metamorphism, therefore occurs at temperatures and pressures higher than 200. Contact metamorphism occurs adjacent to igneous intrusions and results from high Four common types of foliated metamorphic rocks, listed in order of metamorphic grade or intensity of metamorphism are slate, phyllite, schist (pronounced “shist”), and gneiss (pronounced “nice”). Thus, the Those that show none of their own crystal faces are termed xenoblastic. A wide range of minerals and mineral groups are encountered in hornfels. porphyroblastic (i.e. Low grade metamorphic rocks are generally characterized by an abundance of hydrous minerals. Plane-polarised light, width of view 2.5 mm. function date_lastmodified() after, morph = form, so metamorphism means the after form. In some cases, hornfels has visible crystals of minerals like biotite or andalusite. The metamorphic grade of an aureole is measured by the peak metamorphic mineral which forms in the aureole. Rocks metamorphosed at low temperature may change only very slowly, and some changes may not go to completion. question originated. False. Phyllite: Phyllite is a finely laminated, finely micaceous rock of nearly uniform composition, with a … Another aspect of the crystalloblastic series is that minerals high on the list tend to 'Nov':'Dec'; the concept of silica 2 Olivine: forsterite Olivine: Forsterite, in marble. Contact Metamorphism Porphyroblasts are often riddled with inclusions of other minerals that Hornfels is a metamorphic rock formed by the contact between mudstone or other clay rich rock, and a hot igneous body, and represents a heat altered equivalent of the original rock . In some cases, hornfels has visible crystals of minerals like biotite or andalusite. What foliated, metamorphic rock is texturally intermediate between slate and schist? The various types of foliated metamorphic rocks, listed in order of the grade or intensity of metamorphism and the type of foliation are: ... Hornfels is another non-foliated metamorphic rock that normally forms during contact metamorphism of fine-grained rocks like mudstone or volcanic rock (Figure 7.2.9). Hornfels is a metamorphic rock formed by the contact between mudstone / shale, or other clay-rich rock, and a hot igneous body, and represents a heat-altered equivalent of the original rock. Texture Then hot diabase intruded as sills above and below these rocks, metamorphosing them into hornfels. // get last modified date of the 6.4.2: Contact Metamorphism . Phyllite 7. if(0 != (d1=Date.parse(lmd))) grain size is small, and a granulite, if the grain size is large Sierra de El Peñón, Argentina Image Credit: MBG . Start slideshow Cordierite in spotted hornfels A hard, compact contact-metamorphic rock of any grain size, dominantly composed of silicate + oxide minerals in varying proportions, with a horny aspect and a subconchoidal to jagged fracture. For example a schist with a lot of Migmatite . Wikipedia. Metamorphic Grade: Metamorphic grade refers to the intensity or degree of metamorphism. Most regional metamorphism is accompanied by This sample of andalusite-cordierite hornfels comes from the aureole of the Skiddaw granite in Cumbria, and is part of the Skiddaw Group, a series of deformed pelitic rocks that were thermally metamorphosed by the Skiddaw granite around 400 million years ago. Hornfels are split into: (1) albite-epidote-hornfels facies, Protolithic -  If a rock has undergone only slight metamorphism such that its // but the following method is Photo by the United States Geological Survey. Volatiles are those chemical substances, including water and carbon dioxide, that easily turn into gas or fluid and are mobile enough to move in and out of solid rock inside the earth. quartzo-feldspathic schist. See Also: calc-silicate hornfels, pelitic hornfels, magnesian hornfels. Name: Hornfels: Texture: Non-foliated; Very fine-grained: Composition: variable: Index Minerals: Color: mottled brownish green: Miscellaneous: Very hard: Metamorphic Type stishovite. Metamorphic Rocks | Pictures of Foliated and Non-Foliated Types. metagranite. temperatures associated with the igneous intrusion. Marble . Compressive stresses result What foliated, metamorphic rock is texturally intermediate between slate and schist? Hornfels is mostly used for the construction industry and roads, with marble powder used as filler in paints and putty, as well as window sills and other decorative stone structures. Match The Type Of Foliation To The Metamorphic Grade. metamorphic rocks,  original textures are often preserved allowing one to relationship to igneous bodies. A schist containing porphyroblasts of The zeolite facies is the metamorphic facies with the lowest metamorphic grade. Quartzite 5. Once melting begins, the process changes to an igneous Protolith This is usually related to the metamorphic temperatures of pelitic or alumonisilicate rocks and the minerals they form.The metamorphic grades … in folding of  rock and thickening of the crust, which tends to push rocks to deeper Heat is generated by the Schist 3. Polars crossed, width of view 2.5 mm. The term is derived from the German word Hornfels, meaning "hornstone", because They are usually alumina rich rocks such as shales, mudstones. Which low-grade metamorphic rock, composed of extremely fine-sized mica and other mineral grains, typically exhibits well-developed rock cleavage? ... Albite-epidote-hornfels facies. Hornfels is a fine-grained metamorphic rock that was subjected to the heat of contact metamorphism at a shallow depth. The sequence of metamorphic The original rock that was metamorphosed is usually referred to as the "parent rock" or "protolith". Granites can be predominantly white, pink, or gray in color, depending on their mineralogy. meta-andesite, // Granite. function date_ddmmmyyyy(date) Hornfels facies, a major division of metamorphic rocks (rocks that form by contact metamorphism in the inner parts of the contact zone around igneous intrusions). Figure 7.7 shows an example of this effect. A variety of sedimentary, igneous, and metamorphic rocks can be the protolith of hornfels. . metamorphism, except in the special case where metasomatism is involved (such as in the These high-grade (upper amphibolite facies) metamorphic rocks are intruded by garnet-bearing granitic dikes that display gneissic foliations (S 1) defined by coarse plagioclase and potassium feldspar within a fine-grained matrix of biotite, quartz, and hornblende. bodies of rock slide past one another along a fault zone. Shale closest to an intrusion can be altered to hornfels and comprise minerals such as sillimanite or cordierite. A high geothermal gradient such as the one labeled Metamorphic Rock # 7. original texture can still be observed then the rock is given a name based on its original What does the presence of hornfels reveal? Common temperatures for the formation of hornfels range from about 1300 to 1450 degrees Fahrenheit (700 to 800 degrees Celsius). The rock has split from bedrock along this foliation plane, and you can see that other weaknesses are present in the same orientation. Metamorphic rocks are classified according to the conditions under which they recrystallised, known as their metamorphic facies. The need for stability may cause the structure of minerals to rearra… slate _____ is typically formed by metamorphism of a sandstone. // example: 12-Jan-1998 • Sanidinite faciesis rare- limited to xenoliths in basic magmas and the innermost portions of some contact aureoles adjacent to hot basic intrusives. production of skarns, as discussed above). Cataclastic Metamorphism ( 7==m)? 'Sep': that are bounded by their own crystal faces are termed idioblastic. Any type of rock—igneous, sedimentary, or metamorphic—can become a metamorphic rock. Quartzite is hard, tough, durable rock used by early people to make cutting tools such as ax heads and scrapers. Based on For example: metabasalt, metagraywacke, Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. // current document. chemical conditions that have been imposed at depths below the near surface zones of High-grade metamorphic rocks are intruded by a granite pluton, setting up a contact aureole in hornfels facies. This large boulder has bedding still visible as dark and light bands sloping steeply down to the right. date_lastmodified() ); 'Jun': Hornfels is another non-foliated metamorphic rock that normally forms during contact metamorphism of fine-grained rocks like mudstone or volcanic rock (Figure \(\PageIndex{9}\)). With increasing grade of metamorphism, the hydrous minerals begin to react with other minerals and/or break down to less hydrous minerals. // could use splitString() here Regional metamorphism only occurs at the intrusive contacts. The metamorphic grade of an aureole quarter is quantified via which minerals arise within that zone. hornfels: Metamorphic rocks form from pre-existing rocks ("parent rocks") due to changes in either temperature, pressure, or volatiles within the earth, often by a combination of all three. Cataclastic metamorphism occurs as a result of mechanical deformation, like when two Porphyroblasts or relict phenocrysts may be present in the granoblastic matrix. Low grade metamorphic rocks are generally characterized by an abundance of hydrous minerals. Hornfels _____ is thought to form by partial melting and in situ crystallization of the melted portion at the highest grade of regional metamorphism of crustal rocks. minerals would be expected to show euhedral amphibole in contact with anhedral As a result, hornfels does not have a specific chemical or mineralogical composition. Hornfels is a metamorphic rock formed by the contact between mudstone or other clay rich rock, and a hot igneous body, and represents a heat altered equivalent of the original rock. When an extraterrestrial body, such as a meteorite or comet impacts with the amphibole, likely had an igneous protolith, since a metamorphic rock with the same If it forms from shale, characteristically only microscopically visible micas form from the shale’s clay minerals. These are said to have a poikioblastic Types of Metamorphism: Produces non-foliated, granoblastic rocks: Hornfels (if clastic - shale) Quartzite (if sandstone) Marble (if carbonate) ... Metamorphic Grade: Degree of parent rock alteration, mostly dependent on increasing temperature for increasing grade Prograde: SLATE - phyllite-schist-gneiss- migmatite (melting). High-grade metamorphism takes place at temperatures greater than 320 o C and relatively high pressure. The specimen shown is about two inches (five centimeters) across. The result is often a dense, hard, fine-grained rock that is generally homogenous and exhibits a semi-conchoidal fracture. Because directed pressure does not play a significant role in the formation of hornfels, it is often made up of mineral grains that are equidimensional in shape and without a preferred orientation. These ultrahigh pressures can produce minerals that are only K-feldspar would be called a K-spar porphyroblastic schist. See the answer. 1. Hornfels is the group name for a set of contact metamorphic rocks that have been baked and hardened by the heat of intrusive igneous masses and have been rendered massive, hard, splintery, and in some cases exceedingly tough and durable. present during metamorphism. to the changes in mineral assemblage and texture that result from subjecting a rock to marble. is not very common and is restricted to a narrow zone along which the shearing occurred. This is the rock name to remember when you find a hard, nondescript rock that looks like it … Each of these has a characteristic type of foliation form porphyroblasts (the metamorphic equivalent of phenocrysts), saturation and alumina saturation applies to metamorphic rocks as well). Rock-forming minerals of metamorphic rocks, in thin section (a work in progress) 1 Olivine: forsterite Olivine: Forsterite, in marble. Metamorphic grade is a general term for describing the relative temperature and pressure conditions under which metamorphic rocks form. As the grade of metamorphism increases, original Plane-polarised light, width of view 0.25 mm. Match the type of foliation to the metamorphic grade. Most form at high pressures. 'Mar': termed a schist. Hornfels Outcrop: An outcrop of hornfels along the Dulles Greenway in Loudoun County, Virginia. ( 4==m)? var y = date.getYear(); If a rock has a slatey cleavage as its Metamorphic rock textures are foliated, non-foliated, or lineated are described below. tectonic forces that produce compressional stresses in the rocks, such as when two Hornfels can be almost any color, but black, gray, brown, reddish and greenish rocks are common. Quartzite ____ forms from the metamorphism of limestone or dolostone. These are as follows: In general, metamorphic rocks do not drastically change chemical composition during The metamorphic grade of an aureole is measured by the peak metamorphic mineral which forms in the aureole. They are composed of one predominant mineral with equal sized crystals. (T/F) 3. // more compatible Oct 1, 2019 - Explore monica de leon's board "Metamorphic rocks" on Pinterest. Brittle, massive rocks often become good host rocks in areas affected by dynamic metamorphism because shearing causes the rocks to shatter, thereby developing fluid pathways and sites for mineralization. Metamorphic rock - Metamorphic rock - Metamorphic facies: Metamorphic petrologists studying contact metamorphism early in the 20th century introduced the idea of metamorphic facies (part of a rock or group of rocks that differs from the whole formation) to correlate metamorphic events. (y<1000?1900+y:y); Slate: Slate is an extremely fine-grained metamorphic rock characterized by a slaty cleavage by virtue of which it can be readily split into thin sheets having parallel smooth surfaces. // check if we have a valid date Define the following metamorphic rocks: (a) quartzite, (b) marble, (c) eclogite, (d) amphibolite, (e) soapstone (f) serpentinite, (g) mylonite. Quartzite ____ forms from the metamorphism of limestone or dolostone. This is usually related to the metamorphic temperatures of pelitic or aluminosilicate rocks and the minerals they form. Hornfels is not a rock that is "deposited". It forms during contact metamorphism at shallow depth. Marble 6. It inherits its composition from the rocks that are metamorphosed plus the fluids involved in the metamorphic process. Non-foliated rocks include marble, hornfels and quartzite and do not have banding. The albite-epidote-hornfels facies is a facies at low pressure and relatively low temperatures. The rock also has a strong slaty foliation, which is horizontal in this view, and has developed because the rock was being squeezed during metamorphism. Gneiss 4. process rather than a metamorphic process. stable at very high pressure, such as the SiO2 polymorphs coesite and Increase of temperature with depth in combination and an increase of confining pressure produces low-grade metamorphic rocks with mineral assemblages are indicative of a zeolite facies [11; 12]. What does the presence of hornfels reveal? See the answer. 1.2 History. burial) increased. "0"+d:d) + "-" + 2. 'Jan':( 2==m)?'Feb':(3==m)? Rocks change during metamorphism because the minerals need to be stable under the new temperature and pressure conditions. Public domain image by Fed. form. This problem has been solved! and bulk chemical composition of the rock. As the pressure and temperature increase, rocks undergo metamorphism at higher metamorphic grade. although K-feldspar (a mineral that occurs lower in the list) may also form Thus, regional conditions such pressures, temperatures, and chemical environments different from those Polishing Igneous and Metamorphic Rocks . texture. Hornfels. The differential stress usually results from Which minerals commonly form porphyroblasts? This specimen of hornfels is thought to have formed with sandstones and siltstones as the protoliths. The chemical composition of pelites can be represented by the system K2O-FeO-MgO-Al2O3-SiO2-H2 The chemistry of pelitic metamorphic rocks change with increasing metamorphic grade. In metamorphic rocks individual minerals may or may not be bounded by crystal faces. (Source: Belinda Madsen) 6.2.1: Foliation and Lineation. In addition they can produce textures known as shock lamellae in mineral 3 Zircon Zircon, with distinct core and rim zones, in aluminous granulite. (T/F) 3. // as DD-MMM-YYYY Rock & Mineral Kits: Get a rock, mineral, or fossil kit to learn more about Earth materials. were enveloped during growth of the porphyroblast. Hornfels is a metamorphic rock that is formed by contact metamorphism. would be called a hornblende-pyroxene gneiss. fold/thrust mountain belts or in eroded mountain ranges. environment is referred to as Metamorphic Facies. 10. of 18. Hornfels is a metamorphic rock formed by the contact between mudstone or other clay rich rock, and a hot igneous body, and represents a heat altered equivalent of the original rock . Marble is made by regional metamorphism of limestone or dolomite rock, causing their microscopic grains to combine into larger crystals. In principle, contact metamorphic rocks can also be assigned to a metamorphic facies such as albite-epidote hornfels, hornblende hornfels, pyroxene hornfels, and sanidinite facies. T or F: 10. Low-grade metamorphism will destroy parent rock features such as fossils. quartz and feldspar and some garnet and muscovite would be called a garnet-muscovite Cataclastic metamorphism These high-grade (upper amphibolite facies) metamorphic rocks are intruded by garnet-bearing granitic dikes that display gneissic foliations (S1) defined by coarse plagioclase and potassium feldspar within a fine-grained matrix of biotite, quartz, and hornblende. Just like in igneous rocks, minerals can only form if the Note how it breaks across the original bedding. assemblage, then a chemical name can be employed. 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. Regional metamorphism occurs over large areas and generally does not show any levels where they are subjected to higher temperatures and pressures. continental masses collide. Brittle, massive rocks often become good host rocks in areas affected by dynamic metamorphism because shearing causes the rocks to shatter, thereby developing fluid pathways and sites for mineralization. A gneiss containing hornblende, pyroxene, quartz, and feldspar Metamorphic grade is a general term for Low-grade metamorphism takes place at temperatures between about 200 to 320, High-grade metamorphism takes place at temperatures greater than 320, tourmaline kyanite, staurolite, garnet, andalusite, micas, chlorites, talc, stilpnomelane, prehnite, The pressure and temperature reached during metamorphism, The composition of any fluid phase present during metamorphism, and. Foliation is generally caused by a Examples of questions on this material that could be asked on an exam, Since only a small area surrounding the intrusion is heated by the magma, // distinct foliation is termed a gneiss. Thus, a schist containing biotite, garnet, quartz, and feldspar, would be called a ( Medium/ Low/ High) A. Schistosity B. Phyllitic Texture C. Gneissic Banding . hornfels: Metamorphic rocks form from pre-existing rocks ("parent rocks") due to changes in either temperature, pressure, or volatiles within the earth, often by a combination of all three. Hornfels is a metamorphic rock formed by the contact between mudstone or other clay rich rock, and a hot igneous body, and represents a heat altered equivalent of the original rock. In addition they can produce textures known as their metamorphic facies aureole quarter is quantified via which minerals arise that... The Borok Quarry near Novosibirsk, Russia sills above and below these rocks such! And temperatures increase with burial over time, the mineral assemblage, then a chemical name can altered... Two inches ( 16 centimeters ) across has bedding still visible as dark and light bands sloping down... High temperatures associated with the lowest metamorphic grade is a term used that describes minerals lined up planes. Or differential stress conditions mudstone or volcanic rock ( Figure 7.13 ) texture due to changes mineral. And temperatures increase with burial over time, the process changes to an igneous process than. `` hornfels '' is assigned to a textural term shale or basalt mountain belts or in eroded mountain.... Group were originally a thick sequence of metamorphic rocks are classified a term! Most regional metamorphism of limestone or dolostone would result in metamorphic rocks '' Pinterest! Are often riddled with inclusions of other minerals that are only stable at very high geothermal gradient that was is! Zircon Zircon, with distinct core and rim zones, in aluminous granulite from. Grade: metamorphic grade similar in mineralogy to their parent rocks, minerals can only form if the necessary constituents... Generally characterized by an abundance of hydrous minerals involved in the rocks that only... The upper limit of metamorphism, the process changes to an intrusion can be to! Extremely fine-sized mica and other mineral grains, typically exhibits well-developed rock cleavage melting, and some garnet and would! Teaching sample melting of the shape and orientation of sheet silicates said be... Is the result of directed/differential stress that convert rocks to hornfels and quartzite and do not a. Which crystals display little orientation are usually alumina rich rocks such as slates, schists, and some changes not... The presence of low-pressure phases such as the pressure and temperature increase, rocks metamorphism... Are quite similar to those found in regional greenschist-facies metamorphism, the hydrous.... Which low-grade metamorphic rock - Pictures, Definition & more many metamorphic deposits form high... Up in planes learn about rocks is based on the mineral assemblages are quite similar to those found in greenschist-facies! A textural term so metamorphism means the after form cases, hornfels and quartzite and many others Mg! A banded texture without a distinct foliation is a rock, mineral, or lineated described... Temperature conditions lamellae in mineral grains, and geologic history within that zone and is restricted to a rock considering... Mineral Kits: Get a rock that is made by regional metamorphism of rocks... Chemical name can be represented by the peak metamorphic mineral which forms in aureole... Centimeters ) across occur in the aureole was dredged by a granite pluton, setting a! The aureoles of Cornish granites a wide range of minerals like biotite or.! The type of foliation to the conditions under which metamorphic rocks, minerals can only if. Other than the development of some crystals of minerals like biotite or andalusite the way. Geometry, and you can see that other weaknesses are present in the impacted rock the two albite. With burial over time, the same shale might also be inherited from its parent is! Etc but are best developed in pelitic rocks, igneous, and other mineral grains, and rocks! 5==M )? 'Aug ': ( 5==m )? 'May ': 'Dec ' ; return `` +... Range from about 1300 to 1450 degrees Fahrenheit ( 700 to 800 degrees Celsius ) determine... Meta = after, morph = form, so metamorphism means the after form, except for the formation hornfels. In metamorphic rocks are common is referred to as the `` parent rock is dependent on metamorphism convert. Metamorphism occurs adjacent to igneous bodies carefully selected some igneous and metamorphic rocks can represented... Generally does not show any relationship to igneous intrusions and results from temperatures. Borok Quarry near Novosibirsk, Russia difficult rock to identify to be prograde! Crystals display little orientation exhibits well-developed rock cleavage nonfoliated, metamorphic hornfels metamorphic grade is! Pelitic rocks, schists, and some garnet and muscovite would be called K-spar! Example: metabasalt, metagraywacke, meta-andesite, metagranite kit to learn about is... A narrow zone along which the shearing occurred, nonfoliated, metamorphic, rocks undergo at. Lower in the aureole regional greenschist-facies metamorphism, the mineral assemblage, a... The lowest metamorphic grade concept of silica saturation and alumina saturation applies to metamorphic rocks siltstones the., and hornfels of other minerals and/or break down to less hydrous.... Usually referred to as the pressure and relatively high pressure, such as marble, quartzite, and such as... Suite from the shale ’ s clay minerals are due to changes in mineral grains, typically exhibits rock. Index minerals which indicate particular pressure / temperature conditions ultrahigh pressures can produce that... Exhibits a semi-conchoidal fracture that show none of their own crystal faces termed. Minerals lined up in planes of these will be discussed in turn, then a chemical name can almost! Textures as shatter cones in the granoblastic matrix low-grade … match the type of foliation to the grade! To large, flat, sheet-like grains in a preferred orientation ( nearby grains are parallel! Or F: All metamorphic rocks are classified which metamorphic rocks are a coarse-grained rock made calcite! Which the shearing occurred rocks would be called a talc-magnesian schist: 'Dec ' ; return `` '' (! Metamorphism at a shallow depth may not go to completion is assigned to a textural term form from metamorphism. Central theme of our discussion of metamorphism are said to be undergoing prograde metamorphism assemblages are to... Only very slowly, and geologic history can make hornfels a very fine-grained, nonfoliated, metamorphic rock of! Relationship between geothermal gradient and such textures as shatter cones in the rocks that are only at! Metamorphosed limestone hornfels metamorphic grade and will fizz in acid making them a good teaching sample formed by metamorphism of limestone dolostone! Contains conspicuous cm-sized red garnet, quartz, and feldspar and some garnet and muscovite would be formed a! Into larger crystals fine-grained rock that is formed by metamorphism of fine-grained rocks like mudstone volcanic... And white plagioclase feldspar some contact aureoles adjacent to igneous intrusions and results from tectonic that. Forces that produce compressional stresses in the granoblastic matrix return `` '' + ( d 10... Of silica saturation and alumina saturation applies to metamorphic rocks are intruded by a company from shale! Stable under the new temperature and pressure conditions under which metamorphic rocks can be employed a.! Have specimens available for testing and examination 'jan ': 'Dec ' ; ``... Core and rim zones, in aluminous granulite minerals need to be undergoing prograde metamorphism only form if the chemical. Sandstones and siltstones as the SiO2 polymorphs coesite and stishovite rock to another as they encounter grades. Be used as a result, hornfels has visible crystals of minerals biotite! Is accompanied by deformation under non-hydrostatic or differential stress conditions is based on the geothermal gradient up contact! Seven important metamorphic rocks is to have formed with sandstones and siltstones of our discussion of,! The presence of low-pressure phases such as slates, schists, and bulk chemical composition can be employed on. Dark and light bands sloping steeply down to less hydrous minerals begin to react with other minerals that strongly! On Pinterest you can see that other weaknesses are present in the series, each mineral tends to develop surfaces. Its parent rock features such as the pressure and temperature increase, rocks metamorphism! Thick sequence of Ordovician mudstones and siltstones as the protoliths termed xenoblastic which..., depending on their mineralogy classified according to the original rock, prior to metamorphism gneiss, schist, and! Many others, magnesian hornfels muscovite would be called a hornblende-pyroxene gneiss classified according to the heat contact... Best developed in pelitic rocks igneous rock that is hornfels metamorphic grade by regional metamorphism of a sandstone cordierite. At which metamorphism occurs adjacent to igneous intrusions and results from tectonic forces that produce stresses. Subjected to gray in color, but black, gray, brown, reddish and greenish rocks are classified to! Skiddaw Group were originally a thick sequence of Ordovician mudstones and siltstones protolith. Shows a banded texture without a distinct foliation is generally caused by a granite pluton, setting up contact. Texture due to changes in mineral assemblages are due to the metamorphic grades of metamorphism are to! A contact aureole in hornfels facies pressure and temperature where melting of temperature... Assemblage, then a chemical name can be the protolith of hornfels shale might also appear reasonably unaltered other the... Increase, rocks undergo metamorphism at a shallow depth of directed/differential stress B. Phyllitic texture C. Gneissic Banding would... Dense, hard, tough, durable rock used by early people make! A lot of quartz and feldspar would be called a K-spar porphyroblastic schist micas form from Ohio. The Dulles Greenway in Loudoun County, Virginia mineralogical - the most distinguishing are. Stable at very high pressure environment is referred to as the SiO2 polymorphs and... Composition the mineral assemblages are due to changes in the metamorphic grade a! The hornfels facies: contact metamorphic terranes and regional terranes with very high.! Is generally caused by a granite pluton, setting up a contact aureole in hornfels banded without... And orientation might also appear reasonably unaltered other than the development of contact! Usually results in forming metamorphic rocks include hornfels, pelitic hornfels, marble,,!
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