Staurolite
Staurolite (sta"ro*līt) , noun
[Greek stayro`s a cross + -lite.]
(Mineralogy) 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.