Mineral Information and Data:

Chalcocite
Cu2S [CNMNC approved formula]

Named from the Greek for copper.

IMA status : Valid species (Pre-IMA 1832) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
02.04.07.01  
  (02) Sulfides - Including Selenides and Tellurides
  (02.04) where Am Bn Xp, with (m+n):p=2:1
  (02.04.07) Chalcocite Group ([Cu]2-x S] formulae)
  
Nickel-Strunz
(10th edition) :
02.BA.05a
  (02) Sulfides
  (02.B) Metal Sulfides, M:S > 1:1 (mainly 2:1)
  (02.BA) With Cu, Ag, Au
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Unit cell: a = 15.24 Ǻ, b = 11.89 Ǻ, c = 13.50 Ǻ, β = 116.3°
Crystal Habit: Crystals pseudo-hexagonal prisms formed by twinning; short prismatic or thick tabular; massive
Twinning: Twinning: Common on {110} yielding pseudohexagonal stellate forms; also on {032}, {112}. Seen as lamellar twinning in polished section.
  
Color: Blackish gray to black
Diaphaneity: Opaque
Luster: Metallic
Hardness (Mohs): 2.5 to 3
Measured Density: 5.5 to 5.8 g/cm3
Cleavage: 1; {110} indistinct
Tenacity: Brittle, somewhat sectile
Fracture: Conchoidal
Streak: Blackish lead-gray
  
Geologic Setting: An uncommon primary hydrothermal mineral but important as a secondary mineral. Found in or below the zone of oxidation in hydrothermal veins and in large low-grade
porphyry copper ore bodies.
Mineral Association: Pyrite, chalcopyrite, covellite, bornite, molybdenite, many other sulfides and their
alteration products
  
Synonyms/varieties: Chalcosine, redruthite

 

Chalcocite
Pseudohexagonal or twinned, tabular, steel grey crystals to 2 to 5mm.
Origin: Cooks Kitchen mine, Camborne, Cornwall, England
Sample size: 6 x 3 x 4.5 cm
Photo: Tom Loomis

 

Chalcocite
(zoom-in of above)

 

Chalcocite
Origin: Mine #57, Dzhezkazgan, Kazakhstan
Sample size: top 5 x 4 x 3 cm, crystals to 8 mm
Photo: Tom Loomis

 

Chalcocite
(zoom-in of above)

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