Metamorphic rock

Metamorphic rock, one of the 3 main classes of rocks of the earth's crust—the class that has undergone change owing to heat, pressure, or chemical action. In plate tectonic theory the collision of lithospheric plates leads to widespread regional metamorphism. Igneous intrusion leads to changes in the rocks close to the borders or contacts of the cooling magma, and these changes, largely due to the application of heat, constitute contact (thermal) metamorphism. Common metamorphic rock types include marble, quartzite, slate, schist, and gneiss. Some occurrences of granite are also thought to be of metamorphic origin.

See also: Rock.