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Formula: (Cu,Ag)6PbS4
Sulphide
Crystal System: Monoclinic
Specific gravity: 6.74 calculated
Hardness: 3
Colour: Grey
Environments
When heated, furutobeite decomposes at 100+/-2oC into galena plus a solid
solution of CuAgS and Cu2S, which when cooled forms stromeyerite and
chalcocite
(AM 67.1075).
Associated minerals include stromeyerite,
bornite, galena,
sphalerite, tennantite,
digenite and
electrum
(HOM).
Localities
At the type locality, the Furutobe mine, Kosaka, Akita Prefecture, Japan, furutobeite occurs in
bornite-rich ore, as grains 10-300 microns, associated with
bornite, stromeyerite,
galena, sphalerite,
tennantite, and sometimes digenite and
electrum. It is replaced by stromeyerite
(AM 67.1075).
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