Cobaltite
Cobalt arsenic sulfide (CoAsS)
A silver-white cobalt arsenic sulfide that is a leading ore of cobalt, forming bright metallic cubic and pyritohedral crystals.
- Mohs hardness
- 5.5
- Color
- silver-white to reddish-silver, steel-gray, sometimes violet tint
- Type
- mineral
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Overview
Cobaltite is a cobalt arsenic sulfide (CoAsS) and one of the principal ore minerals of cobalt. It often forms striking, well-defined crystals with cubic, octahedral, and pyritohedral shapes, resembling pyrite in form but silver-white in color.
Freshly broken surfaces are bright silver-white, sometimes with a reddish or violet tint, and a metallic luster. Iron commonly substitutes for some cobalt in its structure.
Valued both as an ore and as a collector mineral, cobaltite was historically important as a source of cobalt for blue pigments and is now critical for modern battery and alloy industries.
Formation & geology
Cobaltite forms in high-temperature hydrothermal veins and in contact metamorphic deposits, often associated with other cobalt, nickel, and arsenic minerals such as skutterudite, niccolite, and arsenopyrite, along with sulfides like pyrrhotite and chalcopyrite.
It also occurs in some magmatic sulfide deposits linked to mafic and ultramafic rocks.
Classic localities include the cobalt-silver districts of Cobalt, Ontario in Canada, Tunaberg and Hakansboda in Sweden, Skutterud in Norway, and Cornwall in England. Major modern cobalt resources are tied to the copper-cobalt belt of central Africa.
How to identify it
Look for a silver-white to steel-gray, sometimes reddish-tinted metallic mineral, often as well-formed cubic or pyritohedral crystals with striated faces. It is fairly hard (5.5) and will scratch glass.
The streak is grayish-black. Like other arsenic minerals, it may give off a garlic odor when struck or heated. It can show distinct cleavage.
Look-alikes include arsenopyrite (more elongate crystals), skutterudite, and pyrite (brassy yellow). The silver-white color, crystal habit, hardness, and garlic smell when struck help distinguish cobaltite; specialized testing confirms its cobalt content.
Uses & significance
Cobaltite is an important ore of cobalt, a metal essential for rechargeable lithium-ion batteries, superalloys for jet engines, magnets, and historically for the deep-blue smalt and cobalt-blue pigments used in glass and ceramics.
Mined cobalt also supports catalysts and high-strength, heat-resistant alloys. Because cobaltite contains arsenic, processing requires careful handling.
For collectors, sharp metallic crystals are attractive specimens. It is not used in jewelry. As an arsenic-bearing mineral, specimens should be handled with washed hands and kept away from food.
Frequently asked questions
What is cobaltite used for?
It is a major ore of cobalt, used in rechargeable batteries, superalloys, magnets, and traditionally in blue pigments for glass and ceramics.
Is cobaltite dangerous?
It contains arsenic, so avoid inhaling dust, never ingest it, and wash your hands after handling; solid specimens are safe to display.
How do I identify cobaltite?
Look for silver-white metallic crystals with cubic or pyritohedral shapes, hardness around 5.5, a grayish-black streak, and a garlic smell when struck.
Where is cobaltite found?
Notable sources include Cobalt, Ontario in Canada, Sweden, Norway, and England, with major cobalt resources in central Africa.
Why is cobalt important today?
Cobalt is critical for lithium-ion battery cathodes and high-performance alloys used in aerospace and electronics.
Cobaltite guides
In-depth guides for identifying, valuing, and understanding Cobaltite.
