Mineralogy Photography

Cobaltite

Structural info:

cobaltite

Name origin: Name of the mineral is derived from German – Kolbold meaning “underground spirit” or “goblin” [1]

Description:

Cobaltite is a sulfosalt of cobalt and arsenic that is found in high temperature veins or as a constituent in metamorphosed rocks. The most common form of the crystals are cube and pyritohedron. The mineral crystallizes in orthorhombic (pseudocubic) crystal system but isometric crystal system was firstly suggested by Bragg in 1914. The mineral however undergoes a transition to isometric crystals system at 800-850 °C . This transition results in optical isotropy [2]. A partial disorder of As and S was found in the crystal structure by Le Damany [3]. In the ordered structure of cobaltite each cobalt atom is octagonally coordinated by three arsenic and three sulphur atoms. Both sulphur and arsenic are coordinated tetrahedrally. Arsenic atoms are bonded to three cobalt atoms and one sulphur atom whereas sulphur atoms are surrounded by three cobalt atoms and one arsenic atom in distorted tetrahedral arrangement. The mineral is identified by its higher density of 6.33 g/cm3 and a hardness 5.5 on a Mohs scale. The well known localities of very fine cobaltite specimens are Tunaberg, Sodermanland, Sweden and Mines in the Cobalt and Sudbury districts, Ontario, Canada.

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Cobaltite crystal, Lindesberg, Västmanland, Sweden [photo: Michal Hegedus]

Literature:

[1] Chesterman, Charles Wesley. The Audubon Society Field Guide to North American Rocks and Minerals. New York: Knopf, 1978. Print.
[2] Giese, R. F., J. R. Kerr, and P. F. Kerr. “THE CRYSTAL STRUCTURES OF ORDERED AND DISORDERED COBALTITE.” THE AMERICAN MINERALOGIST, 50 (1965): 1002-014. Print.
[3] Bayliss, Peter. “A Further Crystal Structure Refinement of Cobaltite.” THE AMERICAN MINERALOGIST, 67 (1982): 1048-057. Web.