It depends on the original rock that is metamorphosed. In other samples, lawsonite, jadeite, epidote, phengite, garnet, and quartz are also common. In this hand specimen from Ward Creek, California, glaucophane is the major blue mineral species. Petrologists often prefer to talk about the glaucophane-schist metamorphic facies rather than blueschist, because not all blueschist is all that blue. The bluest, most schistose blueschist-like this example-is made from sodium-rich mafic rocks like basalt and gabbro. Blueschist is a schist because all traces of original structure in the rock have been wiped out along with the original minerals, and a strongly layered fabric has been imposed. High-pressure, low-temperature conditions are most typical of subduction, where marine crust and sediments are carried beneath a continental plate and kneaded by changing tectonic motions while sodium-rich fluids marinate the rocks. These sediments could then be compressed to form sedimentary rocks, which would start the entire cycle anew.Blueschist signifies regional metamorphism at relatively high pressures and low temperatures, but it isn't always blue, or even a schist. At the surface, metamorphic rocks will be exposed to weathering processes and may break down into sediment. This happens due to geologic uplift and the erosion of the rock and soil above them. Limestone, a sedimentary rock, will change into the metamorphic rock marble if the right conditions are met.Īlthough metamorphic rocks typically form deep in the planet’s crust, they are often exposed on the surface of the Earth. Slate is another common metamorphic rock that forms from shale. When granite is subjected to intense heat and pressure, it changes into a metamorphic rock called gneiss. It is usually composed primarily of the minerals quartz, feldspar, and mica. Granite is an igneous rock that forms when magma cools relatively slowly underground. This will result in the formation of an igneous rock, not a metamorphic rock.Ĭonsider how granite changes form. ![]() If there is too much heat or pressure, the rock will melt and become magma. In order to create metamorphic rock, it is vital that the existing rock remain solid and not melt. These conditions are most often found either deep in Earth’s crust or at plate boundaries where tectonic plates collide. Usually, all three of these circumstances are met. The existing rock must be exposed to high heat, high pressure, or to a hot, mineral-rich fluid. The conditions required to form a metamorphic rock are very specific. ![]() Then, due to various conditions within the Earth, the existing rock was changed into a new kind of metamorphic rock. A metamorphic rock, on the other hand, began as a rock-either a sedimentary, igneous, or even a different sort of metamorphic rock. Igneous rocks formed when liquid magma or lava-magma that has emerged onto the surface of the Earth-cooled and hardened. Sedimentary rocks were originally sediments, which were compacted under high pressure. Sedimentary and igneous rocks began as something other than rock. In the rock cycle, there are three different types of rocks: sedimentary, igneous, and metamorphic. ![]() Rocks that undergo a change to form a new rock are referred to as metamorphic rocks. Even rocks, a seemingly constant substance, can change into a new type of rock. However, the word “metamorphosis” is a broad term that indicates a change from one thing to another. The term “metamorphosis” is most often used in reference to the process of a caterpillar changing into a butterfly.
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