Staurolite

Staurolite a silicate of aluminium with peroxide of iron, crystallising in cruciform macles belonging to the Rhombic system, the name being derived from the Greek stauros, a cross. It is generally an opaque. brownish colour, with conchoidal fracture; is infusible; and has a specific gravity of about 3.5 and a hard!less of 7 or 7.5. It occurs in slates and mica-schists as a result of metamorphic action.