polybasite


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polybasite

[‚päl·i′bā‚sīt]
(mineralogy)
(Ag,Cu)16Sb2S11 An iron-black to steel-gray metallic-looking mineral; an ore of silver.
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The stock held surprises too--I'm still evoking in memory the brilliant metallic black miniature of Mexican polybasite, with a great upstanding crystal of 2.5 cm, which was lying, unlabelled, beside the Herkimer diamonds on one front table.
Soon he began shipping some extraordinary silver mineral specimens back to New York, including the largest and best polybasite specimens known, large clusters of "poker chip" stephanite crystals, fine acanthite specimens and a few very fine pyrargyrite specimens.
Pedrazzini to the Egleston Collection at the Columbia School of Mines, where there are also a number of other specimens of polybasite and stephanite, as well as a remarkable specimen representing the transition of an argentite crystal into cerargyrite and a fine embolite.
During the 1890s and the first few years of the 20th century the Las Chispas mine near Arizpe produced some of the world's finest specimens of polybasite, pyrargyrite and stephanite.
Since then Fresnillo has become one of the world's greatest silver districts, and has also yielded superb specimens of crystallized pyrargyrite, stephanite, acanthite and polybasite. The Santo Nino vein, discovered in 1975 and measuring over 3 meters in width, has been the most prolific.
The Smithsonian put in a case of very fine Mexican minerals including such things as stibiconite, amethyst, buergerite, malachite pseudomorphs after azurite, danburite, rare wurtzite and polybasite. Albert Chapman, Australia's leading mineral collector affectionately known as "Chappie," brought his remarkable display, containing some of the finest Australian minerals that many collectors had ever seen.
The specimens were a roll call of silver species: acanthite, pearceite, pyrargyrite, polybasite and many others.
By species and owner/photographer they are: adamite, Schlepp/Currier; wulfenite, Harter/Scovil; legrandite, University of Arizona/Scovil; polybasite, Wallace/Wilson, and amethyst, Schlepp/Wilson.
Mexican sulfosalts were still trickling out of Fresnillo, Mexico; fine stephanite, pyrargyrite, acanthite and polybasite were available.
In the mid-1970's, however, exploratory drilling revealed a hidden system of fabulously rich veins of solid pyrargyrite, acanthite, stephanite and polybasite. During the last decade, Fresnillo has become one of the world's great silver districts.
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).
The polybasite spec imens are similarly iridescent, but are rosettes of very thin, symmetrically offset hexagonal plates; most of these too are thumbnails, but there are two 5-cm miniatures in which the polybasite rosettes reach 3 cm across.