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Formula: (Au,Ag,Sb,Bi,Pb)23(Te,Sb,Bi,Pb)38
bismuthide, gold-,
silver, antimony and
tellurium- bearing mineral
Crystal System: Triclinic
Specific gravity: 9.94 measured
Hardness: 2½
Streak: White
Colour: Yellowish white, light yellow, tin white
Common impurities: Ag,Pb,Bi,S
Environments
Localities
At the type locality, the Robb-Montbray mine, Rouyn-Noranda TE, Abitibi-Témiscamingue, Quebec, Canada, montbrayite is abundant
in some specimens. Freshly broken surfaces show coarsely crystallised aggregates of montbrayite,
tellurobismuthite, altaite,
melonite, gold,
chalcopyrite and pyrite. In polished sections
the following minerals are found in contact with montbrayite or enclosed within it:
altaite, tellurobismuthite,
petzite, gold,
chalcopyrite, melonite and
frohbergite. Altaite, with small amounts of
gold and petzite, occurs in thin stringers cutting
montbrayite. Tellurobismuthite with subordinate
altaite and small patches of petzite forms inclusions
irregularly distributed through montbrayite. Petzite occurs as irregular areas often
surrounding and traversing patches of montbrayite. Subhedral crystals of melonite, with
or without partial rims of petzite, occur in montbrayite. The
chalcopyrite does not occur in the montbrayite itself but at the boundaries of
altaite, tellurobismuthite,
petzite and gold with montbrayite
(AM 34.345-347). Other associated minerals include calaverite,
sphalerite, chalcocite,
covellite and marcasite
(HOM).
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