Phyllite is a type of foliated metamorphic rock primarily composed of quartz, sericite mica, and chlorite; the rock represents a gradation 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 continued metamorphism of slate. The protolith (or parent rock) for a phyllite is a shale or pelite. 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 the regional metamorphic facies.
Contributions by Vsmith, KatieBoundary, and Mikenorton.