Skutterudite

Skutterudite
Skutterudite from Bou Azzer, Morocco
General
Category	Arsenide mineral
Formula (repeating unit)	CoAs3
Strunz classification	2.EC.05
Crystal system	Cubic
Crystal class	Diploidal (m3) H-M symbol: (2/m 3)
Space group	Im3
Unit cell	a = 8.204 Å, Z = 8
Identification
Color	Tin-white to silver-gray, tarnishes gray or iridescent; in polished section, gray, creamy or golden white
Crystal habit	Crystals are cubes, octahedra, dodecahedra, rarely prismatic; in skeletal growth forms, distorted aggregates; also massive, granular
Twinning	On {112} as sixlings and complex shapes
Cleavage	Distinct on {001} and {111}; in traces on {011}
Fracture	Conchoidal to uneven
Mohs scale hardness	5.5 - 6
Luster	Metallic
Streak	Black
Diaphaneity	Opaque
Specific gravity	6.5
References

Named after the city of Skotterud, Norway, Skutterudite is a cobalt arsenide mineral that has variable amounts of nickel and iron substituting for cobalt with a general formula: CoAs₃. Some references give the arsenic a variable formula subscript of 2-3. High nickel varieties are referred to as nickel-skutterudite, previously chloanthite. It is a hydrothermal ore mineral found in moderate to high temperature veins with other Ni-Co minerals. Associated minerals are arsenopyrite, native silver, erythrite, annabergite, nickeline, cobaltite, silver sulfosalts, native bismuth, calcite, siderite, barite and quartz. It is mined as an ore of cobalt and nickel with a by-product of arsenic.

The crystal structure of this mineral has been found to have important technological uses for several compounds isostructural with the mineral.

The mineral has a bright metallic luster, and is tin white or light steel gray in color with a black streak. The specific gravity is 6.5 and the hardness is 5.5–6. Its crystal structure is isometric with cube and octahedron forms similar to that of pyrite. The arsenic content gives a garlic odor when heated or crushed.