A metamorphic rock is a rock that has undergone a mineralogical and structural transformation after an increase in temperature and pressure. There are 3 forms of metamorphism:
A metamorphic rock generally has a well crystallized structure with the appearance of newly formed minerals and a leafed texture.
In the Earth's crust, the solid state transformation of a pre-existing rock under the effect of temperature and pressure, with recrystallization of the minerals. Contact metamorphism, which is localised, is related to the intrusion of igneous rocks; regional metamorphism, which affects a part of the earth's crust, is related to orogenesis.
Schist is a metamorphic rock. © Maksim, Wikipedia CC by sa 3.0
Metamorphic rock - 1 Photo