White crystals of the rare thiosulphate mineral fassinaite from Austria (Erasmus adit, Schwarzleo District, Schwarzleograben, Leogang, Salzburg, Austria) on a dark contrasting matrix. Ex. Erich Laskowski collection (USA). — Photo: David Hospital · CC BY 4.0
Fassinaite
Fassinaite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Pb₂(CO₃)(S₂O₃).
It crystallizes in the orthorhombic crystal system (space group Pnma).
Key properties: Mohs hardness 1.5–2; specific gravity 6.084; White streak; Vitreous to adamantine luster.
IMA symbol Fas, IMA status: approved, named in 2011.
Found as a secondary mineral in the weathering zone of a polymetallic hydrothermal deposit.
It is found associated with Galena, quartz, anglesite (Trentini mine, Italy); galena, cerussite, anglesite, sulfur, phosgenite (Erasmus adit, Austria).
The mineral was named to honor Bruno Fassina (b. 1943), an Italian mineral collector who found the first samples at the Trentini mine.