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Formula: Pb2(CO3)(S2O3)
Thiosulphate - the thiosulphate anion is (S6+O3S2-)2-, ie a sulphate
anion with one O replaced by S
Crystal System: Orthorhombic
Specific gravity: 6.084 calculated
Hardness: 1½ to 2
Streak: White
Colour: Colourless, white
Luminescence: Not fluorescent
Environments
Localities
At the Erasmus adit, Schwarzleo mining district, Schwarzleograben, Hütten, Leogang, Zell am See District, Salzburg,
Austria, fassinaite occurs as a secondary mineral in
the weathering zone of the polymetallic hydrothermal deposit, associated with
galena, cerussite,
anglesite, sulphur and
phosgenite
(HOM).
Fassinaite is found as sprays of colourless, prismatic crystals, up to 0.4 mm long, in fractures in massive
galena, on cerussite, and
anglesite
(AM 98.1079–1080).
Fassinaite from the Erasmus Adit -
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At the Friedrich-Christian Mine, Wildschapbach valley, Bad Rippoldsau-Schapbach, Freudenstadt, Karlsruhe Region,
Baden-Württemberg, Germany, fassinaite is found as small sprays of prismatic crystals up to 0.2 μm in size
in hydrothermal veins containing
lead-zinc ores
(AM 98.1079–1080).
Fassinaite from the Friedrich-Christian Mine
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At the type locality, the Trentini Mine, Contrada Trentini, Monte Naro - Riolo Valley side, Monte Naro,
Torrebelvicino, Vicenza Province, Veneto, Italy, the mineralisation occurs where hydrothermal fluids deposited
sulphides, baryte and iron- and
manganese-bearing minerals at the boundary between volcanic rock and
limestone. The fassinaite is found as radiating aggregates
of acicular, colourless crystals up to 200 μm long, closely associated with
galena, quartz and
anglesite. No twinning has been observed. Fassinaite is
transparent with a vitreous to adamantine lustre, intense internal reflections and a white streak. It is brittle
with an irregular fracture and non-discernible cleavage.
Fassinaite forms as a result of the supergene
alteration of galena; it is likely that thiosulphate formation occurred at
an intermediate stage in the oxidation process as the assemblages moved toward complete oxidation
(AM 98.1079–1080).
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