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Formula: Bi7Te3
Telluride,
tetradymite group
Crystal System: Trigonal
Specific gravity: 8.91 measured, 8.93 calculated
Hardness: 2
Streak: Grey
Colour: Tin-white
Common impurities: Se,S
Environments
Pegmatites
Metamorphic environments
Hydrothermal environments
Hedleyite is typically a late-stage hydrothermal mineral in quartz veins and massive
sulphides associated with skarn and breccia; less
commonly it occurs in pegmatites. Associated minerals include
bismuth, bismuthinite,
tellurobismuthite, tsumoite,
joséite, hessite,
maldonite, gold,
arsenopyrite, pyrrhotite,
chalcopyrite, galena,
sphalerite and pyrite
(HOM).
Localities
At Maldon, Mount Alexander Shire, Victoria, Australia, hedleyite has been found in the goldfield in blebs together with native
bismuth
(AJM 15.35).
São Sebastião das Águas Claras, Nova Lima, Iron Quadrangle, Minas Gerais, Brazil, is a recently discovered
gold deposit in a greenstone belt. Part of its
hydrothermal system is characterised by chaotically distributed tourmaline.
Pyrrhotite and late chalcopyrite occur in the
tourmaline-rich pockets. Bismuth,
bismuth–gold intermetallic aggregates, and
bismuth telluride minerals locally fill microfractures. Hedleyite and the unnamed mineral
Bi8Te3 make up composite aggregates with joséite-B. The
gold-bismuth-tellurium
mineral assemblages indicate precipitation below about 270°C
(CM 53.1061-1072).
At the type locality, the Goodhope mine, Hedley, Osoyoos Mining Division, British Columbia, Canada, the country rock is a
skarn composed mainly of garnet,
epidote and pyroxene, cut by irregular veins and stringers
of quartz. Most of the hedleyite samples were in these
quartz bodies, but some also were noted in the skarn.
Associated minerals include sphalerite, quartz,
bismuth, joséite,
pyrrhotite, molybdenite,
arsenopyrite, calcite,
garnet, epidote,
diopside and gold
(AM 30.644, Mindat).
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