Metamorphic Rock

Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than 150 to 200 °C and, often, elevated pressure of 100 megapascals (1,000 bar) or more, causing profound physical or chemical changes. During this process, the rock remains mostly in the solid state, but gradually recrystallizes to a new texture or mineral composition.

The protolith may be an igneous, sedimentary, or existing metamorphic rock.

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Source: Wikipedia · Image: Wikimedia Commons · CC BY-SA 3.0

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