Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "regulate in form". The native stone (protolith) is subjected to heat (temperatures greater than 150 to 200 °C) and pressure (100 megapascals (1,000 bar) or more), causing complex instinctive or chemical correct. The protolith may be a sedimentary, igneous, or existing metamorphic stone.
Metamorphic rocks make up a large allowance of the Earth's crust and form 12% of the Earth's estate surface. They are classified by texture and by chemical and mineral assemblage (metamorphic facies). They may be formed comprehensibly by subconscious 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 along with formed similar to stone is enraged by the intrusion of warm molten stone called magma from the Earth's interior. The laboratory analysis of metamorphic rocks (now exposed at the Earth's surface subsequent to erosion and uplift) provides counsel roughly 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.