Gneiss is a rock that is only formed by regional metamorphism. It is a coarse-grained, banded rock that is composed of layers of different minerals. Gneiss is formed when sedimentary or igneous rocks are subjected to high temperatures and pressures within the Earth's crust. The high temperatures and pressures cause the minerals in the rock to recrystallize, forming new minerals and new textures. Gneiss is a common rock in mountain belts, where it is often found in association with other metamorphic rocks, such as schist and quartzite.