Chalcocite: Properties and Occurrences

Chalcocite, copper(I) sulfide (Cu2S), is an important copper ore mineral. It has been mined for centuries and is one of the most profitable copper ores. The reasons for this is its high copper content (67% atomic ratio and nearly 80% by weight) and the ease at which copper can be separated from sulfur. It occurs as a secondary mineral in many ore bodies in a zone called the supergene enrichment zone.

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.

General Information

  • Category: Sulfide minerals
  • Formula: copper(I) sulfide: Cu2S
  • Crystal system: Monoclinic
  • Crystal class: Prismatic (2/m) (same H-M symbol)

Properties

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 an orthorhombic crystal system.

  • Color: Dark gray to black
  • Crystal habit: Tabular to prismatic crystals also massive to granular, (pseudo-orthorhombic)
  • Cleavage: Indistinct on {110}
  • Fracture: Conchoidal
  • Tenacity: Brittle to sectile
  • Mohs scale hardness: 2.5 – 3
  • Luster: Metallic
  • Streak: Shiny black to lead gray
  • Diaphaneity: Opaque
  • Specific gravity: 5.5 – 5.8

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.

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. It has been known to form pseudomorphs of the minerals bornite, covellite, chalcopyrite, pyrite, enargite, millerite, Galena, and sphalerite.

 

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