Geffroyite

geffroyite

chameanite

giraudite-(Zn)

clausthalite

Images

Formula: (Cu,Fe,Ag)9Se8
Selenide, pentlandite group
Crystal System: Isometric
Specific gravity: 5.39 calculated
Hardness: 2½
Colour: Bronze-brown
Environments

Hydrothermal environments

Localities

At the type locality, the Chaméane Uranium Deposit, Le Vernet-Chaméane, Issoire, Puy-de-Dôme, Auvergne-Rhône-Alpes, France, geffroyite occurs in a complex quartzitic vein cutting granite. Three stages of mineralisation, separated by brecciation, are recognised. In the first stage pitchblende was deposited with copious baryte gangue; in the second stage quartz with löllingite, arsenopyrite, pyrite, chalcopyrite, tetrahedrite, tennantite and clausthalite were deposited, with partial replacements of baryte by quartz, pitchblende by chalcopyrite, and chalcopyrite by clausthalite. In the third stage the selenides bukovite, athabascaite, umangite, eucairite, eskebornite, more clausthalite, geffroyite, chameanite and giraudite occur with an ankerite gangue, followed by a second generation of chalcopyrite.
Geffroyite occurs in very fine-grained intergrowth with eskebornite, clausthalite, chameanite and giraudite (AM 67.1074-1082).

Geffroyite from Chaméane - Image

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