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Chalcocite from Cornwall
CategorySulfide minerals
(repeating unit)
copper(I) sulfide: Cu2S
IMA symbolCc[1]
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
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}
TenacityBrittle to sectile
Mohs scale hardness2+12–3
StreakShiny black to lead gray
Specific gravity5.5–5.8

Chalcocite (/ˈkælkəˌst/),[6][7] 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 2.5–3 on the Mohs scale. It is a sulfide with a monoclinic crystal system.

The term chalcocite from the Greek khalkos, meaning "copper". It is also known as redruthite, vitreous copper, or copper-glance.[8]


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 (66.7% 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.

See also[edit]


  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Mineralienatlas
  3. ^
  4. ^
  5. ^ Handbook of Mineralogy
  6. ^ "chalcocite". HarperCollins.
  7. ^ "chalcocite". Unabridged (Online). n.d.
  8. ^ Chisholm, Hugh, ed. (1911). "Copper-glance" . Encyclopædia Britannica. Vol. 7 (11th ed.). Cambridge University Press. p. 110.