Chalcocite

Chalcocite (UK: /ˈkælkəˌsaɪt/[5]), copper(I) sulfide (Cu2S), is an important copper ore mineral. It is opaque and dark-gray to black with a metallic luster. It has a hardness of ​2 1⁄2 - 3 on the Mohs scale. It is a sulfide with an orthorhombic crystal system.

Chalcocite
Chalcocite from Cornwall
General
CategorySulfide minerals
Formula
(repeating unit)		copper(I) sulfide: Cu2S
Strunz classification2.BA.05a
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/c
Unit cella = 15.246(4) Å,
b = 11.884(2) Å,
c = 13.494(3) Å;
β = 116.35(1)°; Z = 48
Identification
ColorDark gray to black
Crystal habitTabular to prismatic crystals also massive to granular, (pseudo-orthorhombic)
TwinningCommon on {110} yielding pseudohexagonal stellate forms
CleavageIndistinct on {110}
FractureConchoidal
TenacityBrittle to sectile
Mohs scale hardness2.5 - 3
LusterMetallic
StreakShiny black to lead gray
DiaphaneityOpaque
Specific gravity5.5 - 5.8
Fusibility2-2.5
References[1][2][3][4]

The term chalcocite comes from the alteration of the obsolete name chalcosine, from the Greek khalkos, meaning copper. It is also known as redruthite, vitreous copper and copper-glance.[6]

Occurrence

Chalcocite is sometimes found as a primary vein mineral in hydrothermal veins. However, most chalcocite occurs in the supergene enriched environment below the oxidation zone of copper deposits as a result of the leaching of copper from the oxidized minerals. It is also often found in sedimentary rocks.

It has been mined for centuries and is one of the most profitable copper ores. The reasons for this is its high copper content (66.6% atomic ratio and nearly 80% by weight) and the ease at which copper can be separated from sulfur.

Chalcocite crystals from the Mammoth Mine, Mount Isa - Cloncurry area, Queensland, Australia (size: 3.0 x 2.9 x 2.4 cm)

Since chalcocite is a secondary mineral that forms from the alteration of other minerals, it has been known to form pseudomorphs of many different minerals. A pseudomorph is a mineral that has replaced another mineral atom by atom, but it leaves the original mineral's crystal shape intact. Chalcocite has been known to form pseudomorphs of the minerals bornite, covellite, chalcopyrite, pyrite, enargite, millerite, galena and sphalerite.

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See also

References
  1. Mineralienatlas
  2. Mindat.org
  3. Webmineral.com
  4. Handbook of Mineralogy
  5. https://www.collinsdictionary.com/dictionary/english/chalcocite
  6. Chisholm, Hugh, ed. (1911). "Copper-glance" . Encyclopædia Britannica. 7 (11th ed.). Cambridge University Press. p. 110.


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