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Formula: [Ag9AgS4][Ag6As2S7]
Valence: [Ag1+9Ag1+S1-4][Ag1+6As3+2S1-7]
(reference RRUFF, but surely S2-)
Sulphosalt, sulpharsenite,
pearceite-polybasite group,
silver-bearing mineral
Crystal system: Trigonal
Specific gravity: 6.29 calculated both for the empirical and for the ideal formula
Hardness: 3
Colour: Steel-grey to black
Environments
Metamorphic environments
Hydrothermal environments
Argentopearceite is a relatively new mineral, approved in 2020
Localities
There are two co-type localities, the Lehnschafter mine, Mikulov, Teplice District, Ústí nad
Labem Region, Czech Republic, and the Moldava deposit, Moldava, Teplice District, Ústí nad Labem
Region, Czech Republic.
At the abandoned Lehnschafter mine the ore district is represented by
quartz-dominated hydrothermal As–Ag–Pb veins, located in
gneiss. The majority of the veins contain only the oldest
high-temperature stage of grey quartz with disseminated
pyrite and arsenopyrite, the
younger second stage of druse quartz with common sulphides
(arsenopyrite, galena,
sphalerite, pyrite,
tetrahedrite and
chalcopyrite) is less abundant, and a third stage with Ag-sulphides and
sulphosalts (acanthite,
pyrargyrite, proustite,
miargyrite and argentopearceite) in white
quartz with dolomite and
calcite occurs only sporadically in thicker veins. The total absence of
copper minerals is characteristic of this third stage of mineralisation.
Argentopearceite is associated with proustite in
quartz gangue.
Argentopearceite was also identified in museum samples labelled ‘pearceite’ from the abandoned
fluorite deposit of Moldava. The Moldava deposit is represented by two main
fluorite - quartz -
baryte veins. The vein-filling is massive or contains cavities with green,
yellow and violet fluorite crystals. The strongly
supergene-altered Ag-rich mineralisation includes
acanthite, proustite,
silver, argentopearceite,
galena and tennantite. The
argentopearceite is associated with acanthite and
proustite in fluorite
gangue
Argentopearceite from Mikulov forms irregular aggregates up to 4 mm across in cavities of
quartz gangue, partly composed of
tabular (pseudo)hexagonal crystals up to 0.8 mm in size.
At the Moldava deposit, argentopearceite occurs as groups of steel to dark grey hexagonal tabular crystals up
to 3 mm in size in druse cavities of fluorite
gangue or fine-grained veins and aggregates up to 1 cm in size
(MM 90, 21–32).
Argentopearceite from the Moldava deposit -
Image
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