Lenaite

Images

Formula: AgFeS₂
Valence: Ag¹⁺Fe³⁺S^2-₂
Sulphide of silver and ferric iron, chalcopyrite group
Crystal system: Tetragonal
Specific gravity: 4.63 calculated
Hardness: 4½
Streak: Dark grey to black
Colour: Steel-grey
Environments

Hydrothermal environments

Localities

At Le Rivet Quarry, Peyrebrune, Montredon-Labessonnié, Castres, Tarn, Occitanie, France, lenaite has been found (Mindat photo).
Lenaite from Le Rivet Quarry - Image

At the type locality, the Khachakchan Ag-Sb-Hg deposit, Khachakchan ore cluster, Verkhoyansk Silver Province, Verkhoyansk Fold Belt, Sakha, Russia, lenaite occurs as xenomorphic or equant grains, to 0.2 mm, in goethite pseudomorphs after Mg-rich siderite. The lenaite is associated with acanthite, chalcopyrite and Ag-rich members of the tetrahedrite group, in quartz-siderite veins and veinlets (AM 81.1283).
Other associated minerals include stephanite, Ag-Hg amalgam, galena and goethite (HOM).

The Geis Mine, Cone Butte Sub-District, Warm Springs District, Fergus County, Montana, USA. The Gies deposit is an epithermal vein system that occurs along the contact between alkaline intrusive rocks (monzonite, syenite, and tinguaite) and sedimentary rocks (limestone, sandstone, and siltstone) in the Judith Mountains, Montana. Thirty-six ore and gangue minerals have been identified in four hypogene stages. The first three stages correlate with quartz-forming events, whereas the last three stages contain tellurides. Sulfides are found in all four stages, with lenaite occurring in stage-IV veinlets (<1 mm wide) that cross-cut minerals of stage III. In the sample studied, lenaite occurs as anhedral grains up to 0.2 mm across spatially associated with proustite, tetrahedrite, tennantite, chalcopyrite, and pyrite. Re-examination of another older sample shows the presence of the following ore minerals: hessite, pyrite, lenaite, native gold, chalco pyrite, polybasite, tennantite and the rare phase imiterite. Lenaite occurs in contact with hessite, pyrite, and imiterite, with the imiterite cross-cutting lenaite. Fluid-inclusion studies show that stages I, II, and III formed between 270° and 320°C, and it is assumed from its associated minerals that lenaite formed at less than 170°C The Canadian Mineralogist, 44 (1). 207-212

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