Metamorphism is the process by which existing rocks are transformed physically or chemically at elevated temperature, without actually melting to any great degree. The process occurs due to changes in temperature, pressure, and fluids, and results in rocks with a different mineral composition or texture than the original rock, known as the protolith. There are various forms of metamorphism, including:

• Regional Metamorphism: This is a general term for metamorphism that affects entire regions of the Earths crust. It most often refers to dynamothermal metamorphism, which takes place in orogenic belts (regions where mountain building is taking place), but also includes burial metamorphism, which results simply from rock being buried to great depths below the Earths surface in a subsiding basin.

• Contact Metamorphism: This occurs when rocks are altered due to contact with magma or lava. The heat from the magma or lava causes the surrounding rocks to recrystallize, resulting in a new texture and mineral composition.

• Hydrothermal Metamorphism: This occurs when hot, mineral-rich fluids circulate through existing rocks, altering their mineral composition and texture.

• Shock Metamorphism: This occurs when rocks are subjected to high-pressure shock waves, such as those produced by a meteorite impact. The shock waves cause the rocks to recrystallize and form new minerals.

• Dynamic Metamorphism: This occurs as a result of mechanical deformation, such as when two bodies of rock slide past one another along a fault zone. The resulting textures range from breccias composed of angular, shattered rock fragments to very fine-grained, granulated or powdered rocks with obvious foliation and lineation.

Metamorphism is further divided into prograde and retrograde metamorphism. Prograde metamorphism occurs as temperature and pressure increase, while retrograde metamorphism occurs as temperature and pressure decrease. The grade of metamorphism is a general term for describing the relative temperature and pressure conditions under which metamorphic rocks form.