METAMORPHIC ROCKS

------------------

Metamorphic rocks arise from the transformation of existing rock to new types of rock, in a process called metamorphism.

The original rock is subjected to temperatures greater than 150 to 200 °C (300 to 400 °F) 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 rock may be an igneous, sedimentary, or existing metamorphic rock.