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 &deg;C (300 to 400 &deg;F), and, often, elevated pressure (100 megapascals (1,000 bar) or more), causing profound physical or chemical changes. The protolith may be a sedimentary, igneous, or existing metamorphic rock.