Metamorphism turns the rocks to a denser rock. Once this melted rock cools, igneous rock has been formed. *Classified according to composition and texture. Home; About Oak; People & partners; News & views; Contact; Support and … Recrystallization of the rock will destroy the textures and fossils present in sedimentary rocks. 7. Textures are separated into foliated and non-foliated categories. Metamorphic rocks undergo a progressive transition as the original rock is exposed to increasing heat and pressure. The minute structures, however, disappear, often completely, if the thermal alteration is very profound. This causes the rocks to transform into metamorphic rocks. Rocks are classified by the processes under which they were formed. Many altered rocks of this type were formerly called hornstones, and the term hornfels is often used by geologists to signify those so commonly seen in igneous rocks, because their minerals, being formed at high temperatures, are not so easily transformed or recrystallized. For that reason many of these rocks split readily in one direction along mica-bearing zones (schists). When these are compressed and heated a little, tiny new flakes of mica grow, and tend… Slate (with folded layer) This rock originally consisted of alternating layers of silty material and mud. Metamorphic minerals are those that form only at the high temperatures and pressures associated with the process of metamorphism. How are metamorphic rocks classified? Metamorphic grade is a general term for describing the relative temperature and pressure conditions under which metamorphic rocks form. Sandstones when greatly heated may change into coarse quartzites composed of large clear grains of quartz. How do metamorphic rocks form? This causes the platy or elongated crystals of minerals, such as mica and chlorite, to become rotated such that their long axes are perpendicular to the orientation of shortening. In most cases, this is because they are not buried deeply, and the heat for the metamorphism comes from a body of magma that has moved into the upper part of the crust. Igneous rocks can turn into a metamorphic rock by converting it into magma and cooling it. Foliated Nonfoliated. Metamorphic rock - Metamorphic rock - Pressure: The pressure experienced by a rock during metamorphism is due primarily to the weight of the overlying rocks (i.e., lithostatic pressure) and is generally reported in units of bars or kilobars. Metamorphic Definition. Rocks change during metamorphism because the minerals need to be stable under the new temperature and pressure conditions. As this process happens deep below the surface of the earth, these rocks are often rarer, or at the very least, harder to find on the Earth’s surface, than other types of rock, and only come to light due to geological lift. Metamorphic rocks form from heat and pressure changing the original or parent rock into a completely new rock. Metamorphic rocks can be formed by pressure deep under the Earth's surface, from the extreme heat caused by magma or by the intense collisions and friction of tectonic plates. Like quartz, it maintains a strong crystalline structure, and is very hard and dense. Where do metamorphic rocks form? For other uses, see, Learn how and when to remove this template message, Metamorphic textures – Middle East Technical University, Metamorphic Rocks Tour, an introduction to metamorphic rocks, https://en.wikipedia.org/w/index.php?title=Metamorphic_rock&oldid=994798092, Wikipedia articles incorporating a citation from the 1911 Encyclopaedia Britannica with Wikisource reference, Wikipedia articles incorporating text from the 1911 Encyclopædia Britannica, Wikipedia indefinitely semi-protected pages, Short description is different from Wikidata, Articles needing additional references from January 2012, All articles needing additional references, Creative Commons Attribution-ShareAlike License, This page was last edited on 17 December 2020, at 16:12. The original rock is subjected to very high heat and pressure, which cause obvious physical and/or chemical changes. 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. Metamorphic rocks are formed through immense pressure and heat below the surface of the earth. This means the classification is dependent on the protolith which is used to form the metamorphic rock. What does shale become when heated and put under pressure? The word "metamorphic" comes from Greek and means "To Change Form". Why are these rocks the most dense? In Geology, metamorphic basically pertains to or exhibiting structural change or transformations. The distinction is in the minerals within the original rock. A quartz-porphyry, for example, and a fine feldspathic sandstone, may both be metamorphosed into a grey or pink mica-schist.[4]. 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