Fassinaite

fassinaite

galena

cerussite

phosgenite

Images

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

Hydrothermal environmwnta

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 - Image

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 - Image

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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