THE MINERAL DOMEYKITE

Chemistry: Cu₃As, Copper Arsenide
Class: Sulfides
Subclass: Arsenides
Uses: Mineral specimens, ornamental stone and as a minor ore of copper.
Specimens

Domeykite is a semi-metal alloy of copper and arsenic. It is found at several copper mines in Chile and is named for a nineteenth century Chilean mineralogist named Ignacio Domeyko. Alloys are usually placed in the Elements Class. But domeykite is placed in the Sulfide Class because arsenic is chemically similar to sulfur.

Domeykite can be used in many similar ways to those of native copper. Not only is it used as a minor ore of copper, it is also used for similar ornamental purposes. It is cut and polished and made into attractive cabochons, clocks, bookends and carvings. Its metallic luster and odd color make it a very unusual ornamental stone.

PHYSICAL CHARACTERISTICS:

Color is off-white, yellow-brown, copper-brown to steel-gray.
Luster is metallic.
Transparency: Crystals are opaque.
Crystal System: Isometric, possibly tetragonal; bar 4 2/m.
Crystal Habits include botryoidal, reniform and massive specimens.
Cleavage: Absent.
Fracture: Hackly.
Hardness is 3 - 3.5
Specific Gravity is variable from 7.2 to 8.1 but averages around 7.7 (very heavy even for metallic minerals).
Streak is gray black.
Other Characteristics: Specimens will tarnish easily and cutting or powdering specimens will yield a garlic odor (arsenic).
Associated Minerals include calcite, nickeline, copper and other copper ore minerals.
Notable Occurrences include the type locality of Algodones Mine, Coquimbo, Chile and also the Mohawk Mine, Keweenaw County, Michigan, USA and the copper mines of Ontario, Canada.
Best Field Indicators are color, crystal habit, streak, density and luster.