Metamorphism is defined as the mineralogical, chemical and structural adjustments in solid rocks to physical and chemical conditions which have been imposed due to changes in pressure and temperature or both.
Metamorphism occurs below the surface zones of weathering and cementation.
Conditions of metamorphism differ from the conditions under which the rocks in question were originally formed.
Metamorphism produced as a result of the progressive increase in temperature and pressure, i.e. by burial of a rock within the earth, is termed prograde metamorphism and in general terms is characterized by dehydration reactions, which release water.
With increasing depth of burial the pressure and temperature of the material increases along the follwong gradients:
