Enargite

enargite [e′när‚jīt]

(mineralogy)

A lustrous, grayish-black mineral which is found in orthorhombic crystals but is more commonly columnar, bladed, or massive; hardness is 3 on Mohs scale, specific gravity is 4.44; in some places enargite is a valuable copper ore. Also known as clairite; luzonite.

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Enargite 

a mineral of the sulfide class, with chemical composition Cu₃ AsS₄. Enargite, which contains admixtures of Sb (up to 6 percent), Fe, or Zn, crystallizes in the orthorhombic system, forming steel gray or greenish black tabular or prismatic crystals. Twins are common, while stellated trillings occur less often. The mineral is also found in the form of granular aggregates. Enargite is opaque, with a metallic luster and perfect cleavage in one direction. It has a hardness of 3.5 on Mohs’ scale and a density of 4,300–4,500 kg/m³.

Enargite occurs in hydrothermal average-temperature deposits, such as copper-pyrite, copper-porphyry, and pyrite-enargite deposits. Upon the weathering of enargite, malachite, azurite, copper arsenates, and other minerals form. Enargite, together with other minerals in copper deposits, is a constituent of certain copper ores.