Phyllite is a foliated metamorphic rock primarily composed of quartz, sericite mica, and chlorite. It represents a gradiation in the degree of metamorphism between slate and mica schist. Minute crystals of graphite, sericite, or chlorite impart a silky, sometimes golden sheen to the surfaces of cleavage (or schistosity). Phyllite is formed from the advanced metamorphism of slate. The protolith (or parent rock) for a phyllite is a slate. Its constituent platy minerals are larger than those in slate but are not visible with the naked eye. Phyllites are said to have a "phyllitic texture" and are usually classified as having a low grade in regional metamorphic facies. Phyllite has a pronounced tendency to split into sheets and forms under low pressures and temperatures. Phyllites are usually black, gray or greenish silver. The foliation is commonly crinkled or wavy in appearance.