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The skutterudite Mineral Series
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The Skutterudite series is a group of closely related arsenide minerals with varying rates of cobalt, nickel, and sometimes iron. The cobalt-rich end member is Skutterudite, and the nickel-rich end member is Nickelskutterudite. Another, lesser-known mineral of this series is Ferroskutterudite, a rare iron-rich member.
Chloanthite was originally described as an individual mineral species prior to 1987, after which it was discredited by the IMA and merged into Nickelskutterudite. Smaltite was the former name of the cobalt-rich end member, and this term has now been discredited by the IMA as well. Despite these terms being discredited, they are still occasionally used, and are especially seen on old labels. Smaltite may be used both as a synonym for Skutterudite, or to describe an intermediary member with a similar cobalt and nickel content.
Although most Skutterudite is uninteresting in form, several localities have produced sharp, lustrous crystals that are striking in aesthetics. Skutterudite may partially alter to pink Erythrite, and Ferroskutterudite to green Annabergite. Skutterudite is named after its type locality of Skutterud, Norway. |
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Chemical Formula |
Skutterudite: (Co,Ni)As3
Nickelskutterudite: (Ni,Co)As3 [Arsenic may be slightly deficient in Nickelskutterudite, with a possible formula of (Ni,Co)As3-x]
Ferroskutterudite: (Fe,Co)As3 |
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Composition |
Cobalt nickel arsenide, sometimes with some iron |
| Variable Formula |
(Co,Ni,Fe)As3 |
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Color |
Silver white to gray, occasionally with an iridescent tarnish |
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Streak |
Silver gray |
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Hardness |
5.5 - 6 |
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Crystal System |
Isometric |
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Crystal Forms
and Aggregates |
Crystals are cubic, octahedral, and pyritohedral, though more often in combination of these crystal types. Also forms in sparkly botryoidal and drusy masses. Most often in masses of small crystals, grainy, and massive. |
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Transparency |
Opaque |
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Specific Gravity |
6.4 - 6.9 |
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Luster |
Metallic |
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Cleavage |
3,2 |
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Fracture |
Uneven |
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Tenacity |
Brittle |
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In Group |
Sulfides; Arsenides |
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Striking Features |
Color, streak, crystal habits, and mode of occurrence. |
| Environment |
In mesothermal veins of sulfide deposits. |
| Rock Type |
Sedimentary, Metamorphic |
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Popularity (1-4)
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3 |
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Prevalence (1-3)
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3 |
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Demand (1-3) |
2 |
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Skutterudite is used as an ore of cobalt and nickel. Well-crystallized specimens are highly valued among collectors.
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The Bou Azer District, Morocco, produces the best examples of Skutterudite, in large, lustrous crystals, often in a cuboctadral shape. Good crystals have come from the Schneeberg District in the Erzgebirge, Saxony, Germany; and small interconnected crystals from Manuel-Mercedes Mine, Cala, Andalusia, Spain. In Canada, Skutterudite is found in the orefields at Cobalt, Timiskaming District, Ontario.
Well-formed crystals of Nickelskutterudite have come from the Schlema and Schneeberg Districts, Erzgebirge, Saxony, Germany.
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Arsenopyrite - Forms in different crystal habits, darker streak.Pyrite - Usually has a yellowish color that is lacking in Skutterudite.
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Have a question about Skutterudite? Visit our Q&A Community and ask the experts!
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