A breif description of Metamorphic Rocks.
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Answer:
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Explanation:
A metamorphic rock is a type of rock which has been changed by extreme heat and pressure. Its name is from 'morph' (meaning form), and 'meta' (meaning change). ... The original rock may be sedimentary rock, igneous rock or another older metamorphic rock.
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Answer:
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Explanation:
Metamorphic rocks are pre-existing rocks that have been changed by exposure to unusual temperatures and/or pressures. The pre-existing rocks, called protoliths, may be igneous, sedimentary or other metamorphic rocks. After metamorphosis, these new rocks typically contain distinctive new minerals, reoriented into characteristic patterns. Metamorphic rocks are very common in the Jacksonville area and throughout the entire Appalachian mountain chain, so a knowledge of these rocks is essential.
A. Formation of Metamorphic rocks.
Three general factors influence the changes that take place in rock during metamorphosis. Each of these has a unique effect on the resulting rock. These factors will be considered individually in the next sections.
1. Temperature.
Changes in temperature alter the mineral composition of rocks. Every mineral has a distinctive range of temperature within which it can exist. Beyond this range, the mineral structure breaks down and the atoms create a new mineral stable within this new range. For an analogy, consider a raw egg. A raw egg is stable at room temperature as a runny, slimy, transparent, unusually disgusting substance. What happens if you fry that egg? The egg is not stable at this new temperature. The molecules in that egg rearrange themselves and the slimy raw egg is metamorphosed into a hard, rubbery, opaque fried egg.
Every mineral has a precisely defined range of temperature within which it is stable. For some minerals, this range is very broad. For example, quartz and the feldspars are stable at almost any temperature. Other minerals have very narrow ranges. These minerals are called "index minerals. If we can identify an index mineral in a rock, this tells us the temperature to which that rock was heated.
A rock similar to shale is claystone. The clay minerals in this sedimentary rock are stable under surface conditions, but as temperature increases they break down and rearrange themselves into new, higher-temperature minerals. At about 200 degrees C., the clay transforms into the mineral chlorite. The name schist refers to metamorphic rocks with a certain arrangement of crystals. In this case, the crystals are composed of new mineral chlorite. As temperature continues to increase, chlorite breaks down, the atoms rearrange, and a new mineral is produced called muscovite. Examine the specimen of schist in the metamorphic set. The shiny flat sheets of this silicate should look familiar. As temperature continues to increase, muscovite is destroyed and garnets begin to form. Examine garnet schist. Note the small garnet crystals, shaped like little grains (the word garnet comes from the Greek word for "grain") growing within the rock matrix. If conditions are right, these garnet crystals may grow to the size of softballs. With further increases in temperature, the garnets break down and a very high-temperature mineral called kyanite is formed. You have seen this mineral before ground up to make the white ceramic tops of spark plugs. When automotive engineers needed a ceramic that could survive in extremely hot engine compartments, they turned to a mineral that is stable at very high temperatures. If temperatures continue to rise, the kyanite eventually melts. The resulting rocks are no longer metamorphic, they are igneous.