Cobaltite
Rare cobalt arsenide sulfide, key source of strategic cobalt.
Cobaltite is a mineral combining arsenic and sulfur, with the chemical makeup CoAsS. It gives its name to the cobaltite group, whose members share a crystal structure similar to pyrite (FeS₂). The mineral was documented in 1797 by Klaproth. Its name derives from the element cobalt, which traces back to the German word *Kobold*, meaning an "underground spirit" or "goblin." The idea of "bewitched" minerals arose because cobaltite and related cobalt ores resisted medieval smelting techniques, often releasing foul-smelling, toxic gases. In its natural form, cobaltite appears as a tetartoid—a type of dodecahedron with chiral tetrahedral symmetry. Impurities can include up to 10% iron and varying amounts of nickel. Although uncommon, it is extracted as an important source of the strategically valuable metal cobalt. It is found in high-temperature hydrothermal deposits and contact metamorphic rocks, alongside minerals such as magnetite, sphalerite, chalcopyrite, skutterudite, allanite, zoisite, scapolite, titanite, and calcite, as well as many other cobalt-nickel sulfides and arsenides.
- mineral_formula
- CoAsS
- mineral_group
- Cobaltite group (structurally resembles pyrite)
- common_impurities
- Up to 10% iron, variable nickel
- crystal_form
- Tetartoid (dodecahedron with chiral tetrahedral symmetry)
- associated_minerals
- Magnetite, sphalerite, chalcopyrite, skutterudite, allanite, zoisite, scapolite,
Lore & Background
The name 'cobaltite' traces back to the element cobalt, which itself comes from the German term *Kobold*, meaning an 'underground spirit' or 'goblin.' This connection arose because cobaltite and other cobalt ores resisted medieval smelting methods, often producing foul-smelling, poisonous fumes—hence the notion of 'bewitched' minerals. A variety containing much iron replacing cobalt, known as ferrocobaltite (German: *Stahlkobalt*), was found at Siegen in Westphalia. In India, crystals from Khetri in Rajasthan were used under the name *sehta* by local jewellers to produce a blue enamel on gold and silver ornaments.
Reader's Guide
Cobaltite is mined as a significant source of the strategically important metal cobalt, despite its rarity. It occurs in high-temperature hydrothermal deposits and contact metamorphic rocks, often alongside magnetite, sphalerite, chalcopyrite, skutterudite, allanite, zoisite, scapolite, titanite, and calcite, as well as numerous other Co–Ni sulfides and arsenides. To separate cobaltite from other minerals, selective, pH-controlled flotation methods are used, with cobalt recovery usually involving hydrometallurgy. It can also be processed with pyrometallurgical methods, such as flash smelting. Secondary weathering incrustations of erythrite, a hydrated cobalt arsenate, are common. Major deposits are found in Sweden, Norway, Germany, Cornwall (England), Canada, La Cobaltera (Chile), Australia, the Democratic Republic of the Congo, and Morocco. Crystals from Khetri in Rajasthan, India, were used under the name *sehta* by Indian jewellers to produce blue enamel on gold and silver ornaments.
Did You Know?
- Cobaltite was first described in 1797 by Klaproth.
- Its name comes from the German term *Kobold*, meaning 'underground spirit' or 'goblin,' due to the foul-smelling, poisonous fumes produced during medieval smelting.
- A variety with much iron replacing cobalt, called ferrocobaltite (German: *Stahlkobalt*), was found at Siegen in Westphalia.
- In India, crystals from Khetri in Rajasthan were used under the name *sehta* to produce blue enamel on gold and silver ornaments.
- Secondary weathering of cobaltite often produces incrustations of erythrite, a hydrated cobalt arsenate.
Frequently Asked Questions
What is Cobaltite's composition and what impurities does it typically carry?
Its ideal formula is CoAsS, combining cobalt, arsenic, and sulfur in a single crystal lattice. In natural specimens, up to roughly 10 percent of the cobalt site can be substituted by iron, and variable trace amounts of nickel are also commonly present.
What crystal habit does Cobaltite display?
Cobaltite crystallizes in the tetartoid form, a dodecahedron that exhibits chiral tetrahedral symmetry. This means its faces are arranged so the crystal is mirror-asymmetric, producing distinct left- and right-handed (enantiomorphic) variants.
Why is Cobaltite economically important if it is so rare?
Despite limited global occurrences, Cobaltite is mined as a meaningful source of cobalt, a metal that is strategically critical for lithium-ion batteries, high-temperature superalloys, and other advanced technologies. Its value as a cobalt-bearing ore far outstrips what its relative scarcity might otherwise suggest.
What other minerals is Cobaltite commonly found alongside in the field?
Cobaltite typically occurs in association with magnetite, sphalerite, chalcopyrite, and skutterudite. It has also been recorded alongside allanite, zoisite, scapolite, titanite, and calcite in various ore deposits.
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