Metamorphic Rocks

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

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Metamorphic rock Isua

Metamorphic rock, approximated to be as old together 3.8 billion years, situated near Isua at Qorqut Sound, Greenland.

Photograph through James L. Amos


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The hatchet “metamorphosis” is most often used in referral to the process of a caterpillar an altering into a butterfly. However, the word “metamorphosis” is a vast term that indicates a readjust from one thing to another. Even rocks, a seemingly consistent substance, can readjust into a new type of rock. Rocks the undergo a readjust to form a brand-new rock are described as metamorphic rocks.

In the rock cycle, there are three different species of rocks: sedimentary, igneous, and also metamorphic. Sedimentary and igneous rocks started as something other than rock. Sedimentary rocks were initially sediments, which were compacted under high pressure. Igneous rocks formed when fluid magma or lava—magma that has emerged onto the surface ar of the Earth—cooled and hardened. A metamorphic rock, ~ above the other hand, began as a rock—either a sedimentary, igneous, or also a different sort the metamorphic rock. Then, because of various problems within the Earth, the existing absent was readjusted into a new kind the metamorphic rock.

The conditions required to form a metamorphic rock are really specific. The currently rock have to be exposed come high heat, high pressure, or to a hot, mineral-rich fluid. Usually, all three of these circumstances are met. These conditions are many often discovered either deep in Earth’s crust or in ~ plate borders where tectonic bowl collide. In order to produce metamorphic rock, it is critical that the existing rock continue to be solid and also not melt. If over there is also much warmth 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 transforms form. Granite is one igneous rock that creates when magma cools reasonably slowly underground. It is usually composed mostly of the minerals quartz, feldspar, and also mica. As soon as granite is based on intense heat and pressure, it alters into a metamorphic rock dubbed gneiss.

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

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Although metamorphic rocks typically type deep in the planet’s crust, they are often exposed on the surface of the Earth. This happens because of geologic uplift and also the erosion the the rock and soil over them. At the surface, metamorphic rocks will certainly be exposed come weathering processes and also may break down into sediment. These sediments could then it is in compressed to kind sedimentary rocks, which would start the whole cycle anew.