Enargite

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Enargite
Enargite.jpg
2 cm specimen of Enargite crystals on pyrite from Butte, Montana
General
Category Sulfide mineral
Formula
(repeating unit)
Cu3AsS4
Strunz classification 02.KA.05
Crystal symmetry Orthorhombic pyramidal
H-M symbol: (mm2)
Space group: Pmn21
Unit cell a = 7.407(1) Å, b = 6.436(1) Å,
c = 6.154(1) Å; Z = 2
Identification
Formula mass 393.82 g
Color Grayish black to iron black; gray to pale pink-brown, deep red internal reflections in polished section
Crystal habit Tabular to prismatic crystals, striated parallel to {001}; massive
Crystal system Orthorhombic
Twinning Twin plane {320} common, rarely as interpenetrating pseudohexagonal trillings
Cleavage Perfect on {110}, distinct {100} and {010}
Fracture Uneven
Tenacity Brittle
Mohs scale hardness 3
Luster Metallic to dull
Streak Black
Diaphaneity Opaque
Specific gravity 4.4 to 4.5
References [1][2][3]

Enargite is a copper arsenic sulfosalt mineral with formula: Cu3AsS4. It takes its name from the Greek word enarge, "distinct." Enargite is a steel gray, blackish gray, to violet black mineral with metallic luster. It forms slender orthorhombic prisms as well as massive aggregates. It has a hardness of 3 and a specific gravity of 4.45.

Enargite is dimorph of the tetragonal luzonite.[1]

Occurrence[edit]

It is a medium to low temperature hydrothermal mineral occurring with quartz, pyrite, sphalerite, galena, bornite, tetrahedrite–tennantite, chalcocite, covellite and baryte.[3] It occurs in the mineral deposits at Butte, Montana, San Juan Mountains, Colorado and at both Bingham Canyon and Tintic, Utah. It is also found in the copper mines of Canada, Mexico, Argentina, Chile, Peru, and the Philippines.

Enargite was originally described as a new species from the copper mines of the San Francisco vein, Junin Department, Peru. The name is from Greek έναργής for distinct, in reference to its distinct cleavage.[1][3]

Enargite is related to lazarevicite (named after M. Lazarevic), which has the same chemical formula, but cubic crystalline structure.[4]

References[edit]

External links[edit]

Media related to Enargite at Wikimedia Commons