cobaltite

A mineral having composition (Co,Fe)AsS. Cobaltite is one of the chief ores of cobalt. It crystallizes in the isometric system, commonly in cubes or pyritohedrons, resembling crystals of pyrite. There is perfect cubic cleavage. The luster is metallic and the color silver-white but with a reddish tinge. The hardness is 5.5 (Mohs scale) and the specific gravity is 6.33. Notable occurrences of cobaltite are at Skutterud, Norway; Lunaberg, Sweden; Ravensthorpe, Australia; and Cobalt, Ontario, Canada. See also Cobalt.

Environment

Very uncommon, in sulfide veins with other cobalt and nickel ores. Well-developed single crystals stud some metamorphic rock.

Silvery crystals, well formed, in cubes and pyritohedrons resembling pyrite. Also granular, massive.

Tin-white. Luster metallic; hardness 5Ɖ; specific gravity 6-6.3; fracture uneven; cleavage good cubic. Brittle.

Cobalt sulfarsenide (35.5% Co, 45.2% As, 19.3% S).

After powdering, fuses on charcoal with difficulty, giving off sulfur and faint arsenic (garlic) fumes and forming magnetic granules. Grains partially dissolve in warm nitric acid giving clear pink to red solution; residue remains metallic in luster.

The tin-white color, coupled with the cubic or pyritohedral crystal form, is unmistakable. Cobaltite is harder and has a less perfect cleavage than galena. It is historically rare.

An insignificant ore of cobalt with two unusual crystal occurrences. Large, 1-in. (2.5 cm) or more, well-formed pyritohedral crystals were found at Tunaberg, Sweden, and Skutterud, Norway. Unexciting granular masses are found in veins at Cobalt, Ontario, mixed with (and hard to distinguish from) several white cobalt and nickel arsenides.

Cobalt gets its name from the word kobold (German, Kobalt ) given to imps that were imagined to live underground and thwart the miners; today we might call them gremlins.

Cobaltite
Cobaltite from Sweden
General
Category	Sulfosalt mineral
Chemical formula	CoAsS
Identification
Color	Reddish silver white, violet steel gray to black
Crystal habit	Granular to massive, rarely as striated crystals
Crystal system	Orthorhombic, pseudocubic.
Twinning	About [111] creating pseudo-cubic forms and striations
Cleavage	Good in three directions
Fracture	Brittle
Mohs Scale hardness	5.5
Luster	Metallic
Streak	Grayish-black
Specific gravity	6.33
Optical properties	Opaque
Other characteristics	magnetic after heating
References	[1][2]

Cobaltite is a sulfosalt mineral composed of cobalt, arsenic and sulfur, CoAsS. It contains up to 10 percent iron and variable amounts of nickel.^[3] Structuraly it resembles pyrite (FeS₂) with one of the sulfur atoms replaced by an arsenic atom.

Although rare it is mined as a significant source of the strategically important metal cobalt. Secondary weathering incrustations of erythrite, hydrated cobalt arsenate, are common.

The name is from the German, Kobold, "underground spirit" in allusion to the refusal of cobaltiferous ores to smelt properly.^[4]

It occurs in high temperature hydrothermal deposits and contact metamorphic rocks. It occurs in association with magnetite, sphalerite, chalcopyrite, skutterudite, allanite, zoisite, scapolite, titanite, calcite along with numerous other Co–Ni sulfides and arsenides.^[1] It was described as early as 1832 and its type locality is Cobalt, Ontario.^[2]

It is found chiefly in Sweden, Norway, Germany, Cornwall, England, Canada, Australia, Democratic Republic of the Congo and Morocco.^[1][3]

References

1. ^ ^{a b c} http://rruff.geo.arizona.edu/doclib/hom/cobaltite.pdf Mineral Handbook
2. ^ ^{a b} http://webmineral.com/data/Cobaltite.shtml Webmineral data
3. ^ ^{a b} Klein, Cornelus and Cornrlius Hurlbut, 1996, Manual of Mineralogy, 20th ed., Wiley, p.288, ISBN 0-471-80580-7
4. ^ http://www.mindat.org/min-1093.html Mindat

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