Cobaltite is a sulfide mineral composed of cobalt, arsenic, and sulfur, CoAsS. It is a sulfosalt mineral, containing sulfur, arsenic, and cobalt. The mineral was named after the German word Kobold, which means “underground spirit” or “goblin”, representing its elemental composition. It was discovered as early as 1832 from mines in the Cobalt district, Ontario, Canada.
It contains up to 10% 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.
- Category: Sulfide mineral
- Formula: CoAsS
- Crystal system: Orthorhombic
- Crystal class: Pyramidal (mm2) (same H-M symbol)
Cobaltite can be identified in the field by a range of colors, from reddish-silver-white to violet-steel-gray, and black. It is opaque, non-fluorescent, and magnetic after heating. Its fractures are brittle, as that of non-metallic minerals and glasses. It has a density of 6.33 g/cm3, and a hardness of 5.5.
- Color: Reddish silver white, violet steel gray to black
- Crystal habit: Granular to massive, rarely as striated crystals, pseudocubic.
- Fracture: Uneven
- Tenacity: Brittle
- Mohs scale hardness: 5.5
- Luster: Metallic
- Streak: Grayish-black
- Diaphaneity: Opaque
- Density: 6.33 g/cm3
Cobaltite occurs in high-temperature hydrothermal deposits, as veins in contact metamorphosed rocks, and as dissemination. Calcite, titanite, scapolite, zoisite, allanite, skutterudite, chalcopyrite, sphalerite, and magnetite are the minerals that are analogous to cobaltite.
It occurs in high-temperature hydrothermal deposits and contact metamorphic rocks. It occurs in association with magnetite, sphalerite, chalcopyrite, skutterudite, allanite, zoisite, scapolite, titanite, and calcite along with numerous other Co–Ni sulfides and arsenides. It is found chiefly in Sweden, Norway, Germany, Cornwall, England, Canada, Australia, the Democratic Republic of the Congo, and Morocco.