CARROLLITE (COBALT-NICKLE SULFIDE): TUCSON PUEBLO SHOW

Another large venue with a variety of dealers is the Pueblo Gem and Mineral Show held in the Riverpark Inn area west of the Interstate.  Here hundreds of deals hawk everything from beads to rocks and minerals to fine jewelry.  I examined most of the booths except the scattered dealers that were wholesale only areas. Some show dealers situated were in large free-standing tents such as the table below in a large area of Madagascar dealers while other, more local dealers, erected small shelters about 10 x 10 feet.  I found these smaller dealers much more personable and willing to visit about their minerals.  I fact, I picked up small green and blue tourmaline crystals from one.  However, most dealers (hundreds of them) were tightly packed into the “main pavilion tents.”  After gazing at the merchandise, mostly jewelry and metaphysical paraphernalia, for a few hours everything began to look the same and it was time to bail.

One of the well-stocked tables of "lots of things" displayed in a large tent occupied by dealers from Morocco.

A table of absolutely gorgeous slabs of cut and polished labadorite (a potassium feldspar, semi gemstone).

You can take your quartz home polished as a sphere or in large crystals.

Besides the tourmaline crystals noted above I picked up a hand sample of crystalline calcite containing several shiny, metallic-looking crystals of a copper cobalt/nickel sulfide [Cu(Co,Ni)₂S₄].  Somewhere in the back recesses of my mind a little card popped up and said, “copper sulfide, check Butte notes.”  In doing so, I remembered reading about carrollite when writing about the Butte, Montana, sulfides of covellite, djurleite, chalcocite, and digenite.  Although common at some African localities, it seems not present at two famous covellite [CuS] localities in the United States, the Leonard Mine near Butte, Montana and the Summitville District in Colorado. 

The photomicrograph does not do justice to the mirror faces of this altered cube, maybe a cubo-octahedron., of carrollite (C). A gemmy poker chip of calcite (Ca) is attached at lower right.  The calcite rhombs (CA) form the matrix.  I don't have the slightest idea what the small green crystals (?) scattered on the matrix represent. Width of carrollite crystal ~3.2 mm.

Close-up, at least as close as my camera will permit, of tiny, cloudy, greenish?, submillimeter crystals on matrix. 

~ 3 mm modified cube crystal of carrollite on calcite matrix.

~3 mm. modified cube of carrollite.  The Ch is a distant particle of chalcopyrite (Ch).

This is carrollite but it is massive and without crystal forms.

More massive carrollite but a larger hunk of chacopyrite (Ch) along with the unknown ? tiny ??cubes.

Carrollite has a bright silver color (sometimes more steel in color), a very definite metallic luster (often mirror-like), a hardness of ~4.5 (Mohs), a gray-black streak and virtually no cleavage or fracture pattern (uneven). Crystals belong to the Isometric System and often appear as modified cubes.  Although I do not understand the occurrence, some pods of carrollite in the calcite matrix appear to resemble melted “blobs.”  Unlike many other copper sulfides, carrollite does not seem to tarnish.

 Carrollite has some interesting solid solution partners (Wagner and Cook, 1999).  The copper in carrollite has a valance of +1 while the cobalt has a +++3; however, in one solid solution series Co++ can substitute for the monovalent copper + so we go from Cu⁺(Co,Ni⁺⁺⁺)₂S₄ to Co⁺⁺Co⁺⁺⁺₂S₄ [also noted as Co₃S₄], the mineral linnaeite.  I wish to be a better chemist and understand how that change works!  Carrollite occurs in hydrothermal veins along with many other copper sulfides but there must be some sort of phase relationships (temperature, pressure) that govern its crystallization.

My specimen of carrollite came from the Kamoya South II Mine, Kamoya, Kambove District, Democratic Republic of the Congo.  This large open pit mine evidently produces most of the carrolite specimens coming from Africa (or from any place).  The mine is located in the Katanga Copper Crescent and further situated in the larger Central African Copper Belt.  The ore bodies in the Kambove District are hosted by late Precambrian metasedimentary rocks associated with fold and thrust faults in a rifting basin.  Although the cobalt content in carrollite is not high, it was/is a major ore mineral at the mine.

One little bit of trivia here, linnaeite, the close relative of carrolite was recently discovered in newly formed rocks of the Mi-Atlantic Ridge (Lee and others, 2002).

REFERENCES CITED

Wagner, T. and N.J. Cook, 1999, Carrollite and related minerals of the linnaeite group: solid solutions and nomenclature in light of new data from the Siegerland district, Germany. Canadian Mineralogy vol. 37.

Lee, S. Y., Watanabe, M., Hoshino, K., Oomori, T., Fujioka, K., and P. A. Rona, 2002,. First report of linnaeite (Co₃S₄) and millerite (NiS) from active submarine hydrothermal deposits: Rainbow hydrothermal field, Mid-Atlantic Ridge at 36˚ 14'N. Neues Jahrbuch für Mineralogie-Monatshefte, vol. 1.