Geographic Minerals

Carrollite: Properties and Occurrences

Carrollite: Properties and Occurrences

Carrollite, CuCo2S4, is a sulfide of copper and cobalt, often with the substantial substitution of nickel for the metal ions, and a member of the linnaeite group. It is named after the type locality in Carroll County, Maryland, US, at the Patapsco mine, Sykesville.

Carrollite occurs in hydrothermal vein deposits associated with tetrahedrite, chalcopyrite, bornite, digenite, djurleite, chalcocite, pyrrhotite, pyrite, sphalerite, millerite, gersdorffite, ullmannite, cobaltoan calcite, and with linnaeite group members linnaeite, siegenite, and polydymite.

General Information

  • Category: Sulfide mineral
  • Formula: CuCo2S4
  • Crystal system: Isometric
  • Crystal class: Hexoctahedral (m3m)


Carrollite can be identified in the field by its color variations, such as gray, copper red, light gray, and steel. Its opaque form has {001} indistinct cleavage and a metallic luster. The fracture of this mineral is conchoidal.

The density of carrollite is 4.5 – 4.8 g/cm3, with a hardness of 4.5 to 5.5 – approximate to near apatite.

  • Color: Light to dark gray, rarely tarnishes to copper red or violet gray
  • Crystal habit: Octahedral and cubic crystals, also massive, granular or compact
  • Cleavage: Imperfect on {001}
  • Fracture: Conchoidal, subconchoidal or uneven
  • Tenacity: Very brittle
  • Mohs scale hardness: 4.5 to 5.5
  • Luster: Metallic
  • Streak: Grey black
  • Diaphaneity: Opaque. R is 43% to 45% for lambda = 560 nm
  • Specific gravity: 4.5 to 4.8 measured, 4.83 calculated


Carrollite occurs in hydrothermal vein deposits.

Carrollite is found worldwide; reported in Australia, Austria, Azerbaijan, Brazil, Bulgaria, Canada, Chile, China, the Czech Republic, the Democratic Republic of Congo, France, Germany, Japan, Morocco, Namibia, North Korea, Norway, Oman, Poland, Romania, Russia, Slovakia, Sweden, Switzerland, US and Zambia.

It is often associated with minerals such as tetrahedrite, linnaeite, siegenite, polydymite, digenite, pyrite, chalcopyrite, bornite, chacocite, pyrrhotite, sphalerite, millerite, gersdorffite, ullmannite, cobaltoan calcite, and djurleite.


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