Enargite

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
General
CategorySulfide mineral
Formula
(repeating unit)		Cu3AsS4
Strunz classification2.KA.05
Crystal systemOrthorhombic
Crystal classPyramidal (mm2)
H-M symbol: (mm2)
Space groupPmn21
Unit cella = 7.407(1), b = 6.436(1)
c = 6.154(1) [Å]; Z = 2
Identification
ColorGrayish black to iron black; gray to pale pink-brown, deep red internal reflections in polished section
Crystal habitTabular to prismatic crystals, striated parallel to {001}; massive
TwinningTwin plane {320} common, rarely as interpenetrating pseudohexagonal trillings
CleavagePerfect on {110}, distinct {100} and {010}
FractureUneven
TenacityBrittle
Mohs scale hardness3
LusterMetallic to dull
StreakBlack
DiaphaneityOpaque
Specific gravity4.4 to 4.5
References[1][2][3]

Enargite is dimorph of the tetragonal luzonite.[1]

Occurrence

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 ("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
  1. http://www.mindat.org/min-1380.html Mindat
  2. http://webmineral.com/data/Enargite.shtml Webmineral
  3. Handbook of Mineralogy
  4. "Lazarevicite on Mindat". Retrieved 2009-06-06.

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