Metamorphic Rock
Metamorphic rock is the transformation of an existing rock type, in a process called metamorphism, which means "change in form". The rock is subjected to heat and pressure temperatures greater than 150 to 200 °C and pressures of 1500 bars causing physical and/or chemical change. The rock may be Sedimentary rock, Igneous rock or another older Metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and are classified by texture and by chemical and mineral gathering. They may be formed simply by being deep beneath the Earth's surface, subjected to high temperatures and the great pressure of the rock layers above it. They can form from tectonic processes such as continental collisions, which cause horizontal pressure, friction and distortion. They are also formed when rock is heated up by the intrusion of hot molten rock called magma from the Earth's interior. The study of metamorphic rocks now exposed at the Earth's surface following erosion and uplift provides information about the temperatures and pressures that occur at great depths within the Earth's Crust. Some examples of metamorphic rocks are gneiss, slate, marble, schist, and quartzite.