Aktashite

Aktashite is a rare arsenic sulfosalt mineral with formula Cu₆Hg₆As₄S₁₂. It is a copper mercury-bearing sulfosalt and is the only sulfosalt mineral with essential Cu and Hg yet known. It is of hydrothermal origin. It was published without the approval of the IMA-CNMNC, but recognize as valid species by the IMA-CNMNC Sulfosalts Subcommittee (2008).

General Information

Category: Sulfosalt
Formula: Cu₆Hg₆As₄S₁₂
Crystal system: Trigonal
Formula mass: 1667.51 g/mol

The composition and structure of aktashite from the Aktash deposit, Gorny Altai, Russia, have been studied by electron microprobe and X-ray structural analysis. On the basis of close compositions and crystal structures, the identity of aktashite from the Gal-Khaya and Aktash deposits has been demonstrated.

Physical Properties of Aktashite

Lustre: Metallic
Transparency: Opaque
Color: Gray-black
Comment: white in reflected light
Streak: black
Hardness: 3½ on Mohs scale
Hardness: VHN50 = 300 – 346 kg/mm² – Vickers
Tenacity: Brittle
Cleavage: None Observed
Fracture: Irregular/Uneven, Conchoidal
Density: 5.5 g/cm³ (Measured) and 5.72 g/cm³ (Calculated).

The structure of aktashite as a framework of vertex-shared HgS₄ − and CuS₄− tetrahedrons of the same orientation is intimately related to the sphalerite-type structure. The earlier identified uncommon cluster group [As₄] has been verified and its parameters have been refined. It is shown that the structure may be represented as construction blocks (As₄S₁₂)₁₂− packed according to the law of the distorted cubic I-cell.

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