ABSTRACT
This chapter shows how an unconsolidated sediment becomes an indurated rock. Metamorphism is a group of processes that affects a rock in the solid state; it does not involve a transformation to a magma. The principal factors that control metamorphism are pressure, temperature, and fluid activity; they are interdependent. The modification processes are more effective if they occur over a long period of time. Metamorphism creates a wide variety of rocks. Pressure and temperature conditions and geochemical fluxes are highly variable depending on their geologic settings and all types of rocks can be metamorphosed. The internal structures of sedimentary rocks, such as fossils or sedimentary structures, are partially or completely obliterated by recrystallization. Various terms are used to describe the anisotropic nature of metamorphic rocks, but their definitions are rather ambiguous. The term foliation is used to characterize intensely metamorphosed rocks that have an alternation of layers of different mineralogy.
