Metamorphic rock Metamorphic rock Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form". The original rock (protolith) is subjected to heat (temperatures greater than 150 to 200 °C) and pressure ( or more), causing profound physical or chemical change. The protolith may be a sedimentary, igneous, or existing metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and form 12% of the Earth's land surface. They are classified by texture and by chemical and mineral assemblage (metamorphic facies). They may be formed simply by being deep beneath
Overburden pressure in practice for most near-surface applications which require an assessment of lithostatic pressure. In deep-earth geophysics/geodynamics, gravitational acceleration varies significantly over depth and "g" may not be assumed to be constant. This should be compared with the equivalent concept of hydrostatic pressure in hydrodynamics. Overburden pressure Overburden pressure, also called lithostatic pressure, confining pressure or vertical stress, is the pressure or stress imposed on a layer of soil or rock by the weight of overlying material. The Oxford Dictionary of Earth Sciences describes 'confining pressure' as "the combined hydrostatic stress and lithostatic stress; i.e. the total weight of the interstitial