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Formula: Pb21.7Sn9.3Fe4.0Sb8.1S56.9
Sulphosalt
Crystal System: Triclinic
Specific gravity: 5.90 measured, 5.88 calculated
Hardness: 2½ to 3
Streak: Greyish black
Colour: Grey-black, black; iridescent at times
Common impurities: Zn,Ag,Ge,In
Environments:
Metamorphic environments
Hydrothermal environments
Franckeite is a rare sulphosalt containing antimony and
tin, which occurs in hydrothermal
silver-tin deposits and in
limestone
contact metamorphic deposits
(Webmin).
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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