Pyrite: Gemstone Information
Pyrite is the cubic form of FeS2 and dimorphous with marcasite (q.v.).It forms numerous forms of which the cubic pyritohedral, octahedral and combinations are frequent. Striations conform to pyritohedral symmetry; penetration and contact twins and granular and stalactitic masses are also common. The hardness is 6–6.5 and the SG 5.01–5.03.Pyrite is paramagnetic and a semiconductor. The colour is pale brass yellow, tarnishing to a darker colour with iridescence and the lustre metallic and splendent. Pyrite forms under a number of different conditions and in many different rock types. Material appropriate for ornament may be found in almost any deposit. The ‘marcasite’ of the jeweller is pyrite.