Metamorphic rocks are formed mainly in the lithosphere or crust and upper mantle, wherever there is high pressure and high temperature. If the pressure and temperature are too high, metamorphic rock will melt and become igneous. Metamorphic rocks are most abundant at convergent plate boundaries, but can occur in other areas where there are increased pressures and/or temperatures.

Sedimentary rocks form only on the surface of the Earth. Sedimentary rocks form in two main ways, from clastic material (pieces of other rocks or fragments of skeletons) that are cemented together, and by chemical mechanisms including precipitation and evaporation. There are many environments associated with sedimentary rock formation including oceans, lakes, deserts, rivers, beaches, and glaciers. They may form at all types of plate boundaries, but the thickest sedimentary rock accumulations occur at convergent plate boundaries. Fossils are associated with sedimentary rocks.

Metamorphic rocks from Canadian shield

Sedimentary rocks from Canyon de Chelly, Arizonia