gallobeudantite

The discovery of gallobeudantite is credited to the late Mark N. Feinglos (1948-2020) who submitted a specimen in his collection (originally labelled as "fleischerite") for study. The specimen is believed to have been collected c. 1960 but with the location in the mine unrecorded. Analysis demonstrated the presence of a gallium analogue of beudantite, IMA 1994-021, which was described by Jambor et al. (1986) and named for its composition. Gallobeudantite is the gallium analogue of beudantite in which Fe³⁺ is replaced by Ga³⁺. Polished sections used in characterising gallobeudantite are conserved at the Canadian Museum of Nature and the Geological Survey of Canada, in Ottawa while the holotype specimen remains in the Feinglos Collection (now at Harvard University (MGMH 2020.7.5980T). It should be noted that the Feinglos specimen is also the source of the holotype for calvertite.

Gallobeudantite occurs as transparent pale yellow, greenish or cream-coloured zoned rhombohedral crystals, up to 200 µm on edge, in a vug in massive copper sulphide ore. Zones of Ga-rich beudantite and hidalgoite, and the un-named Ga analogues of segnitite, corkite, kintoreite and arsenocrandallite are present in some of the crystals (Jambor et al. 1996).

On the type specimen, which is believed to be from the second oxidation zone, gallobeudantite occurs in inconspicuous vugs in blackish massive copper sulphide ore comprising inclusions of renierite in a granular copper-rich germanite-like material (later described as calvertite), with minor gallite (as inclusions in the renierite) and a gallium-rich tennantite. The calvertite has rims of chalcocite and all of the sulphide minerals are cut by hairline veinlets of chalcocite. Other secondary minerals associated with the gallobeudantite are goethite and hematite, with sparse crystals of stolzite (Jambor et al. 1996).

Gebhard (1999) described sub-mm disc-like crystals of yellow gallobeudantite on brownish gallium-rich scorodite.

beudantite; calvertite; chalcocite; germanite; goethite; hematite; hidalgoite; otjisumeite; renierite; scorodite; segnitite; silver; stolzite; tennantite-(Zn)