Cobaltite

Cobaltite
Cobaltite from Sweden
General
Category	Sulfide mineral
Formula (repeating unit)	CoAsS
Strunz classification	2.EB.25
Crystal system	Orthorhombic
Crystal class	Pyramidal (mm2) (same H-M symbol)
Space group	Pc21b
Unit cell	a = 5.582 Å, b = 5.582 Å, c = 5.582 Å; Z = 4
Identification
Color	Reddish silver white, violet steel gray to black
Crystal habit	Granular to massive, rarely as striated crystals, pseudocubic.
Twinning	About [111] creating pseudo-cubic forms and striations
Cleavage	Perfect on {001}
Fracture	Uneven
Tenacity	Brittle
Mohs scale hardness	5.5
Luster	Metallic
Streak	Grayish-black
Diaphaneity	Opaque
Density	6.33 g/cm³
References

Cobaltite is a sulfide mineral composed of cobalt, arsenic and sulfur, CoAsS. It contains up to 10 percent iron and variable amounts of nickel. Structurally 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 as they are expected to.

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. It was described as early as 1832.

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