Maldonite

minerals

gold

bismuth

joseite

Formula: Au2Bi
Alloy, copper group
Specific gravity: 15.46
Hardness: 1½ to 2
Colour: Silver white with pink tint, tarnishes to black
Stability: Thermodynamically unstable below ~116°C, but is found in a metastable state in nature (Mindat).
Common impurities: Ag
Environments

Hydrothermal environments

Maldonite occurs in gold - bismuth - telluride - sulphide assemblages (AJM 15.25-38).

Localities

At the type locality, Nuggety Reef, Maldon, Mount Alexander Shire, Victoria, the country rocks hosting the quartz reefs in the gold field consist of quartzite and hornfels with occasional calc-silicate rocks and skarn. The sequence of mineralisation is within the biotite - cordierite - K-feldspar zone of a contact aureole surrounding granite.
Assemblages of native bismuth, gold, maldonite, joséite and bismuthinite are dominated by gold and native bismuth; other minerals found in the assemblages include jonassonite, aurostibite and hedleyite. The maldonite occurs as blebs up to 2 mm across surrounded by an irregular fringe of intergrowths of gold and bismuth (AJM 15.25-38).

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