Metamorphism is the process that changes existing rocks (called protoliths) into new rocks with new minerals and new textures. Increases in temperature and pressure are the main causes of metamorphism...Metamorphism is the process that changes existing rocks (called protoliths) into new rocks with new minerals and new textures. Increases in temperature and pressure are the main causes of metamorphism, with fluids adding important mobilization of materials. Grade describes the amount of metamorphism in a rock, and facies are a set of minerals that can help guide an observer to an interpretation of the metamorphic history of a rock.
