Chromite

Chromite, Chromic Iron, or Chrome Iron Obe, is an oxide of chromium, aluminium, iron and magnesium. It is hardly fusible alone, but with borax gives a chrome-green bead. It crystallises in regular octahedra, but is more commonly massive, sub-metallic, black, opaque, brittle, and sometimes magnetic. Hardness = 5.5. Specific gravity = 4.3 to 4.5. Chromite occurs chiefly in serpentinites and other rocks rich in magnesia, and is the principal source of the salts of chromium.