Geographic Minerals



Domeykite is a copper arsenide mineral, Cu3As. It is a semi-metal alloy of copper and arsenic. It crystallizes in the isometric system, although crystals are very rare. Alloys are usually placed in the Elements Class. But domeykite is placed in the Sulfide Class because arsenic is chemically similar to sulfur.

It was first described in 1845 in the Algodones mines, Coquimbo, Chile. It was named after Polish mineralogist Ignacy Domeyko (1802–1889) by Wilhelm Haidinger.

General Information

  • Category: Arsenide mineral
  • Formula: Cu3As
  • Crystal system: Isometric
  • Crystal class: Hextetrahedral (43m)


It typically forms as irregular masses or botryoidal forms. It is an opaque, white to gray (weathers brassy) metallic mineral with a Mohs hardness of 3 to 3.5 and a specific gravity of 7.2 to 8.1. Its metallic luster and odd color make it a very unusual ornamental stone.

  • Formula mass: 265.56 g/mol
  • Color: Tin-white to steel-gray
  • Tenacity: Brittle – sectile
  • Mohs scale hardness: 3-3.5
  • Luster: Metallic
  • Streak: Black gray
  • Diaphaneity: Opaque
  • Specific gravity: 7.2 – 8.1, average = 7.65

Occurrence and Uses

It is found at several copper mines in Chile and is named for a nineteenth-century Chilean mineralogist named Ignacio Domeyko.

Domeykite, being a minor copper ore is used for obtaining copper. It can also be polished and used for ornamental purposes.


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