Skutterudite
Cobalt arsenide ((Co,Ni)As3)
A metallic cobalt-nickel arsenide, an important cobalt ore, named for the Skutterud mines of Norway.
- Mohs hardness
- 5.5-6
- Color
- Tin-white to silver-gray, tarnishes gray
- Type
- mineral
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Overview
Skutterudite is a cobalt arsenide, (Co,Ni)As3, that crystallizes in the cubic system. It is a metallic, tin-white to silver-gray mineral that often tarnishes to gray or iridescent hues, and it forms a series with the nickel-rich variety nickelskutterudite.
Named after the Skutterud mines in Norway, it is an important ore of cobalt and nickel. Older literature uses the names smaltite and chloanthite for arsenic-deficient members of the group.
Beyond its economic role, skutterudite has attracted modern scientific interest as a thermoelectric material capable of converting heat into electricity.
Formation & geology
Skutterudite forms in moderate-temperature hydrothermal veins, typically associated with other cobalt, nickel, silver, and arsenic minerals. It crystallizes from mineralizing fluids in fracture-filling vein systems.
It commonly occurs alongside cobaltite, nickeline (niccolite), native silver, arsenopyrite, and erythrite (the pink cobalt bloom that signals its presence).
Classic localities include Skutterud (Norway), the Cobalt district of Ontario (Canada), the Erzgebirge of Germany, Bou Azzer (Morocco), and Schneeberg in Saxony. The Moroccan deposits are renowned for fine crystallized specimens.
How to identify it
Skutterudite is identified by its metallic luster, tin-white to silver-gray color, cubic and octahedral crystal forms, and high density. It has a hardness of 5.5 to 6 and a black to grayish-black streak.
Fresh surfaces are bright and metallic but commonly tarnish to gray or develop pinkish erythrite coatings, a strong clue to its cobalt-arsenic chemistry.
It resembles cobaltite, arsenopyrite, and nickeline; the presence of pink erythrite (cobalt bloom) or green annabergite (nickel bloom) on associated specimens helps confirm a cobalt-nickel arsenide. Heating releases a garlic-like arsenic odor.
Uses & significance
Skutterudite is an important ore of cobalt and nickel, metals essential for batteries, superalloys, magnets, and pigments. Historically it was mined for cobalt used to produce blue glass and ceramic colorants.
In modern materials science, skutterudite-structured compounds are studied as high-performance thermoelectric materials for waste-heat recovery and power generation, making the mineral name scientifically prominent.
For collectors, well-formed crystals, especially from Morocco and the historic European districts, are desirable. Because it contains arsenic, specimens should be handled carefully and not powdered or ingested.
Frequently asked questions
What metals does skutterudite contain?
It is primarily a cobalt-nickel arsenide and serves as an ore of both cobalt and nickel, with arsenic as a major constituent.
What is the pink coating sometimes seen on skutterudite?
That is erythrite, a pink cobalt arsenate weathering product known as cobalt bloom, which indicates a cobalt-bearing arsenide nearby.
Why is skutterudite important in technology?
Skutterudite-structured compounds are promising thermoelectric materials that convert heat into electricity, useful for waste-heat recovery.
Is skutterudite safe to handle?
It contains arsenic, so avoid inhaling dust, do not ingest it, wash your hands after handling, and store it away from food and children.
Skutterudite guides
In-depth guides for identifying, valuing, and understanding Skutterudite.
