Metamorphic rocks (from the Greek meta, change, and morphe, form, "change of shape") 1 are rocks formed by the modification of other pre-existing ones inside the Earth through a process called metamorphism. Through heat and / or pressure, in chemically active fluids the transformation of rocks occurs that undergo structural and mineralogical adjustments.2 The agents of metamorphism make it possible for igneous rocks, sedimentary rocks or other metamorphic rocks, when they are subjected to pressures ranging from less than 1000 to up to 16,000 bar, at temperatures ranging from 200 to 1000 ° C, 3 and / or an active fluid, cause changes in their composition, adding new substances to them. The rock that is generated will depend on the composition and texture of the original rock, the time it was subjected to the effects of the so-called metamorphic process, as well as the agents of the same metamorphism.1 The precursor of a metamorphic rock is called protolith.
