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Formula: [Ag9AuS4][Ag6Sb2S7]
Valence: [Ag1+9Au1+S2-4][Ag1+6Sb3+2S2-7]
Sulphantimonite,
pearceite-polybasite group,
silver-, gold- and
antimony- bearing mineral
Crystal System: Trigonal
Specific gravity: 6.622 calculated
Hardness: About 3
Streak: Black
Colour: Dark grey to black
Environments
Auropolybasite is a new mineral, approved in 2024 and to date (January 2026) it has been reported only from
the type locality. It is the first member of the
pearceite-polybasite group with essential Au.
(AM 109.2173-2174)
Localities
At the type locality, Šibeničný vrch, Nová Baňa, Žarnovica District, Banská Bystrica Region, Slovakia,
auropolybasite and auropearceite were found as anhedral grains up to
0.2 mm in size, usually rimmed by acanthite. Other associated minerals include
argentopolybasite,
argentopearceite,
pyrargyrite, proustite,
stephanite, selenostephanite,
rozhdestvenskayaite-(Zn),
zvěstovite-(Zn),
zvěstovite (Fe),
naumannite, Au-Ag alloys,
uytenbogaardtite,
iodargyrite and bromargyrite.
They are dark grey to black, opaque, with a black streak and metallic lustre. They are brittle with no observable cleavage
and with a conchoidal fracture.
auropolybasite and auropearceite form in the waning stages of
epithermal systems, from reduced, S-rich and low-salinity fluids that transport Au, Ag, Sb and As in the form of
thiocomplexes ("thio" is a prefix used in chemistry to indicate the presence of sulphur in a compound). These fluids are
unable to transport Cu, Pb or Zn, thus explaining the chemical composition of these minerals and the entire mineral
assemblage
(AM doi:10.2138/am-2025-9806).
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