Staurolite

n. [ Gr. stayro`s a cross + -lite. ] (Min.) A mineral of a brown to black color occurring in prismatic crystals, often twinned so as to form groups resembling a cross. It is a silicate of alumina and iron, and is generally found imbedded in mica schist. Called also granatite, and grenatite. [ 1913 Webster ]