Phyllite

Phyllite a type of foliated metamorphic rock formed from slate that further metamorphosed so that very fine grained white mica achieves a preferred orientation. It primarily composed of quartz, sericite mica, and chlorite.

Phyllite has good fissility (a tendency to split into sheets). Phyllites are usually black to gray or light greenish gray in color. The foliation commonly crinkled or wavy in appearance.

The word comes from the Greek phyllon, meaning “leaf”.