Skutterudite

Formula: CoAs_2-3

Origin of name: after locality Skutterud, Norway

Crystal system: cubic

Crystal class: 2/m -3

Twinning: on {112} sixlings, also on {011}

Unit cell: a = 8.204 Å

Colour: tin-white, may tarnish iridescent or gray

Diaphaneity: opaque

Luster: metallic

Habit: crystals cubic, octahedral, cubo-octahedral, rarely pyritohedral, reticulated shapes, distorted aggregates, massive

Hardness: 5.5 to 6

Specific gravity: 6.1 to 6.9

Cleavage: 3; {001} and {111} distinct, {011} trace

Tenacity: 

Streak: black

Synonyms/varieties: smaltite (As-poor variety)

Comments: series with nickel-skutterudite