Metamorphic Rocks

Metamorphic rocks start as one form of rock and—with pressure, heat, and also time—gradually change into a new kind of rock.

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Metamorphic absent Isua

Metamorphic rock, estimated to be as old as 3.8 billion years, located near Isua at Qorqut Sound, Greenland.

Photograph by James L. Amos


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The term “metamorphosis” is most frequently used in recommendation to the procedure of a caterpillar changing into a butterfly. However, words “metamorphosis” is a large term that shows a change from one thing to another. Even rocks, a seemingly continuous substance, can change into a new type of rock. Rocks the undergo a readjust to kind a new rock are referred to as metamorphic rocks.

In the rock cycle, there room three different varieties of rocks: sedimentary, igneous, and metamorphic. Sedimentary and also igneous rocks began as something other than rock. Sedimentary rocks were originally sediments, which to be compacted under high pressure. Igneous rocks developed when fluid magma or lava—magma that has arised onto the surface ar of the Earth—cooled and hardened. A metamorphic rock, on the other hand, began as a rock—either a sedimentary, igneous, or also a various sort the metamorphic rock. Then, due to various conditions within the Earth, the existing rock was changed into a brand-new kind the metamorphic rock.

The problems required to form a metamorphic absent are very specific. The present rock should be exposed to high heat, high pressure, or come a hot, mineral-rich fluid. Usually, all three of these circumstances are met. These conditions are many often uncovered either deep in Earth’s late or at plate limits where tectonic plates collide. In order to create metamorphic rock, that is an important that the currently rock stay solid and not melt. If there is also much heat or pressure, the rock will certainly melt and also become magma. This will result in the development of an igneous rock, not a metamorphic rock.

Consider exactly how granite alters form. Granite is an igneous absent that develops when magma cools relatively slowly underground. The is usually composed primarily of the mineral quartz, feldspar, and also mica. Once granite is subjected to intense heat and also pressure, it changes into a metamorphic rock dubbed gneiss.

Slate is an additional common metamorphic absent that creates from shale. Limestone, a sedimentary rock, will change into the metamorphic absent marble if the right conditions are met.

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Although metamorphic rocks typically form deep in the planet’s crust, castle are frequently exposed ~ above the surface of the Earth. This happens as result of geologic uplift and the erosion the the rock and soil over them. In ~ the surface, metamorphic rocks will be exposed come weathering processes and also may breakdown into sediment. These sediments can then be compressed to type sedimentary rocks, which would begin the whole cycle anew.