APPeaRANCE OF METAMORPHIC ROCKSRocks that are formed through regional metamorphism are commonly foliated, but in contact metamorphism, if the protolith was already foliated, this characteristic can't be destroyed. This means that the rocks has ribbonlike layers of strips in different colours and textures from different minerals particles that was gained. Contortion or crumbling of the foliation is not uncommon, hence the layers can be curved and straight. to result in ribbonlike layers, Foliation occurs when a rock is within the Earth's interior and is under intense pressure that is unbalanced. Meaning that there is greater pressure one direction than the others. This causes the rock to be shortened along one axis and having curved ribbonlike layers. however, to result in non-foliated rocks, the pressure are equal in all directions. Another significant identification of most Metamorphic rocks is that they contain crystals, as the mineral particles grow slowly over the years. On the other hand, no Metamorphic Rocks will ever contain fossils, as they could not survive the heat and pressure.
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formation of metamorphic rocks |
Metamorphic rocks are formed under the surface of the earth from the metamorphosis (change) that occurs due to intense heat and pressure. The rocks that result from these processes often have ribbonlike layers and may have shiny crystals, formed by minerals growing slowly over time, on their surface. At the start of this process, the original type of rock is exposed to an intense temperature ( 150+) from the intrusion of hot molten rock called magma from the Earth's interior that is hot enough for the rock to reach its melting point, but not too high that the rock itself becomes magma as well. As extrem heat and pressure can cause the mineralogy, the texture and the chemical composition to change, the protolith can result in fantastic chemical and physical changes that effects the texture and the structure of the rock. The study of metamorphic rocks which is now exposed at the Earth's surface following erosion and uplift, provides information about the temperatures and pressures that occur at great depths within the Earth's crust. Metamorphic rocks are used in sculptures. They are also used for construction, building, paving and in jewellery. Metamorphic rocks can be composed of important minerals and ores. Metamorphic rocks can be studied, and a lot can be found out, as all minerals are stable within certain limits. Therefore, new minerals can be formed by the reaction and metamorphosis of other minerals when they cannot stand the conditions any longer. Geologists can use this knowledge to find out the approximate temperature and pressure that formed the metamorphic rock.
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types of 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. The heat and the contact with hot magma changes the minerals and texture the rock. 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 horn stones, and the term hornfels is often used by geologists to signify those fine-grained, compact, non-foliated products of contact metamorphism. In contact metamorphism, there is a tendency of metasomatism between the igneous magma and sedimentary country rock. This is when the chemicals from the rocks are exchanged or introduced into one another.
Regional metamorphism, also known as dynamic 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. |