The skutterudite Mineral Series
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.
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
Properties
Streak
Silver gray |
Hardness
5.5 - 6 |
Transparency
Opaque |
Specific Gravity
6.4 - 6.9 |
Luster
Metallic |
Cleavage
3,2 |
Fracture
Uneven |
Tenacity
Brittle |
Uses
Skutterudite is used as an ore of cobalt and nickel. Well-crystallized specimens are highly valued among collectors.
Noteworthy Localities
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.
Distingushing Similar Minerals
Arsenopyrite - Forms in different crystal habits, darker streak.Pyrite - Usually has a yellowish color that is lacking in Skutterudite.