Phyllite

Phyllite (/ˈfɪlaɪt/ FIL-yte) is a type of foliated metamorphic rock formed from slate that is further metamorphosed so that very fine grained white mica achieves a preferred orientation.

[citation needed] The minute crystals of graphite,[3] sericite, or chlorite, or the translucent fine-grained white mica,[1] impart a silky,[1] sometimes golden[citation needed] sheen to the surfaces of cleavage, called "phyllitic luster".

Its constituent platy minerals are larger than those in slate but are not visible with the naked eye.

Cemetery markers, commemorative tablets, creating artworks and writing slates are some of its commercial uses.

A type of Carolina slate, Duke stone, is a dacitic phyllite that is fractured and colored with iron oxide.