Editorial Feature

Carrollite – Occurrence, Properties, and Distribution

Carrollite was named after its occurrence in Carroll Co. Maryland, USA. It belongs to the linnaeite group.

Properties of Carrollite

The following are the key properties of carrollite:

  • Cell Data
    • Space group: Fd3m
    • a = 9.458
    • Z = 8

  • Crystal Data
    • Cubic
    • Point group: 4/m 3 2/m
    • Octahedral crystals, to 10cm
    • Commonly massive, disseminated granular to compact
    • Twinning: On {111}; may show polysynthetic twin lamellae
    • X-ray powder pattern: 2.86 (100), 1.674 (80), 1.825 (60), 2.37 (50), 0.994 (50), 3.35 (40), 1.234 (30)

  • Chemical Composition
    Elements Content 1 Content 2 Content 3 Content 4
    S 41.2 40.74 40.64 41.89
    Co 38.6 35.15 35.79 36.08
    Cu 20.2 13.90 18.98 9.98
    Fe 0.6 0.93 2.25 -
    Ni 0.3 7.01 3.66 7.65
    insol. 0.27 0.50 - -
    Total 100.9 99.25 100.00 98.35

  • Optical Properties
    • R: (400) 41.4, (420) 41.5, (440) 41.6, (460) 41.8, (480) 42.0, (500) 42.3, (520) 42.6, (540) 42.9, (560) 43.1, (580) 43.3, (600) 43.5, (620) 43.9, (640) 44.3, (660) 44.7, (680) 45.0, (700) 45.3

  • Estimated Properties
    Electron density Bulk density (electron density) = 4.60 g/cm3
    note: Specific gravity of carrollite = 4.83 g/cm3
    Photoelectric PECarrollite = 24.99 barns/electron
    U=PECarrollite x ρ electron density= 115.04 barns/cm3
    Fermion index Fermion index = 0.0041788352
    Boson index = 0.9958211648
    Radioactivity
    Carrollite is not radioactive

How to Identify Carrollite

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 on 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.

Global Distribution

Carrollite is distributed in the following places:

  • USA - From Carroll Co. Maryland; in the Patapsco mine, Finksburg; and the Mineral Hill mine, Sykesville
  • Mexico - At Boleo, Baja California
  • Bulgaria - From near Chernomorets, Burgas
  • Chile - In the Carrizal Alto copper district, Atacama
  • Slovakia - At Vysna Boca, Nizke Tatry Mountains
  • Germany - In the Kohlenbach mine, near Eiserfeld, and throughout the Siegerland district, North Rhine-Westphalia
  • Sweden - From Gladhammar, Kalmar
  • Japan - In the Sazare mine, Ehime Prefecture, and the Shirataki mine, Kochi Prefecture
  • North Korea - At the Hol Kol Au–Cu mine, about 75km southeast of Pyongyang, Suan Co.
  • Namibia - At Tsumeb
  • Zimbabwe - At the Madziwa (Dry Nickel) mine, Bindura, and Shamva
  • Congo - Large crystals from Kambove, and in the Kamoto and Musonoi mines, near Kolwezi, Katanga Province
  • Zambia - From the Rokana mine, Kitwe
  • Australia - From Kambalda, 56km south of Kalgoorlie, Western Australia

Occurrence of Carrollite and Useful Mineral Association

Carrollite occurs in hydrothermal vein deposits.

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.

References

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