Specific gravity: 5.90
Hardness: 2½ to 3
Streak: Greyish black
Colour: Grey-black, black; iridescent at times
Common impurities: Zn,Ag,Ge,In
Franckeite is a rare sulphosalt containing antimony and
tin, which occurs in hydrothermal
silver-tin deposits and in
limestone contact metamorphic deposits
At Llallagua, Bustillo province, Potosí, Bolivia, franckeite occurs primarily as a minor component of pyrite/marcasite replacement of pyrrhotite, usually in association with marcasite and wurtzite. In one portion of the Contacto vein franckeite is associated with pyrite, arsenopyrite, wurtzite and cylindrite. In the Inca vein it has been found associated with cassiterite (MinRec 37.2.137).
At the type locality, the Chocaya mine, Atocha-Quechisla mining district, Sud Chichas Province, Potosí, Bolivia, franckeite occurs in a hydrothermal silver-tin deposit (Mindat, HOM), associated with cylindrite, teallite, plagionite, zinkenite, cassiterite, wurtzite, pyrrhotite, marcasite, arsenopyrite, galena, pyrite, sphalerite and siderite (HOM).
In the Sinantscha zinc deposit, Sichota-Alin, and from Smirnowsk, Transbaikalia, Russia, franckeite is associated with cassiterite, galena, stannite, teallite and cylindrite (HOM).
At the Kalkar quarry, Santa Cruz county, California, USA, franckeite occurs in a limestone contact metamorphic deposit (HOM).
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