Sometimes high temperatures and pressures cause the crystallization or the recrystallization of pre-existing rocks. Modifications of rocks into the solid state create new rocks called “metamorphic” rocks.

The type of metamorphic rock formed depends on the composition of the original rock, the temperature, pressure, and the amount of water already present or subsequently introduced.

The further one penetrates below the earth’s surface, the hotter the temperature is.

Metamorphism in the interior of fold mountain ranges where heat is high in a very large area. it is closely linked with deformation.

Increasing pressure is due to the overlying masses and to stress.

The most common rocks created by the process of metamorphism are slate, mica-schist and gneiss.