Domeykite-alpha: Gemstones Information
Domeykite-alpha is Cu3As and forms reniform or botryoidal masses of the cubic system with hardness 3–3.5 and SG 7.2–7.9. The ornamental value is due to the surface which shows a metallic lustre and is tin-white to steel-grey, slowly tarnishing to yellowish, then to orange-brown, finally developing an attractive iridescence. Above 90° the material inverts to domeykite-beta, a hexagonal form. Domeykite is usually of hydrothermal origin and occurs with algodonite (q.v.) with which it is often intergrown. A major location is the Mohawk mine, Keweenaw County, Michigan, USA.Domeykite-alpha is the cubic form of Cu6As and forms reniform or botryoidal masses of the cubic system with an opaque steel-white colour and metallic lustre.