freibergite


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freibergite

[′frī‚bər‚gīt]
(mineralogy)
A steel-gray, silver-bearing variety of tetrahedrite.
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In the Keyue deposit, the ore minerals include sphalerite, galena, pyrite, arsenopyrite, chalcopyrite, tetrahedrite, freibergite, boulangerite, jamesonite, bournonite, and stibnite; the gangue minerals are mainly Mn-Fe carbonate, quartz, and calcite (Figures 4-6); and the supergenesis generates the minerals that prevailingly include ferrohydrite, sardinianite, valentinite, malachite, and siliceous sinter (Figure 7).
When Ag atoms exceed Cu atoms, however, the mineral is called freibergite, which is very rare worldwide.
The economic mineralisation of Real de Angeles consists of silver-bearing galena, argentite and sphalerite/marmatite with subordinate amounts of chalcopyrite and freibergite. The gangue sulphides are pyrrhotite, pyrite and arsenopyrite.
The main silver-bearing minerals include nature silver (Figure 4(c)), argentite, and acanthite, and minor freibergite and sternbergite are also reported [13].
Other collectible species include: native silver, pyrargyrite, argentiferous tetrahedrite, freibergite, sphalerite, galena, quartz, siderite, pyrite, marcasite, boulangerite, jamesonite, acanthite, cerussite, hawleyite (type locality), barite and anglesite.
Of course, each browser among the Currier cases had one or two favorite specimens: it was interesting to hear comments such as "Wow, look at that tourmaline!" or "I'd like to own that California gold!" or "How about that freibergite on pyrite from Bolivia!" Yes, and how about those huge pyrite octahedrons from Huanzala, Peru, or those 5-cm doubly terminated ludlamite crystals from Bolivia, or those tetrahedrite crystals to 16 cm from the Morococha District, Lima Department, Peru?
The silver is present as inclusions in the galena with minor amounts of polybasite, freibergite, pyrargyrite and matildite.
It yields primarily small specimens of crystallized pyrargyrite, with rarer miargyrite (in nearly black, lens-shaped crystals), polybasite (in hexagonal plates), stephanite and freibergite (both in complex, gray, highly lustrous crystals).
Freibergite is a rare member of the tetrahedrite group in which silver predominates over copper and iron in the cation sites; good crystals have always been rare, and must in any case be analytically verified as freibergite, as they cannot be visually distinguished from tetrahedrite or tennantite.
Freibergite [(Ag,Cu,Fe).sub.12][(Sb,As)sub.4][S.sub.13]