Waiting for the snow to melt…
Raindrops on roses and whiskers on silver: the truth(?)behind primary acanthite Bruce Geller and Bob Jordan Over 120 years ago, argentite was first reported in Colorado (Endlich, 1878).Since that time, all of the argentite studied in Colorado has been found to be acanthite, the monoclinic form of silver sulfide, which is the stable form of Ag2S below 177°C (?).In Colorado, acanthite is usually found in secondary enriched zones of epithermal silver-base metal deposits such as the limestone replacements at Leadville and Aspen or the veins at Creede; however, it has been reported from at least 27 additional districts and undoubtedly occurs sporadically throughout the state (Eckel et al., 1997).Collectable and much sought after silver-bearing minerals such as native silver, Ag-sulfides (primarily acanthite, stromeyerite, and jalpaite), Ag-sulfosalts (primarily pyrargyrite, pearceite, matildite, polybasite, schirmerite, proustite, and stephanite), Ag-tellurides (primarily hessite, petzite, and sylvanite), and Ag-halides (primarily bromargyrite-chlorargyrite) are known from many mining districts within Colorado (Eckel et al., 1997).The most famous of these districts include: Caribou, Gold Hill, and Ward in Boulder County; Georgetown-Silver Plume in Clear Creek County; Rico in Dolores County; Gold Brick in Gunnison County; Creede in Mineral County; Montezuma in Park and Summit Counties; Aspen in Pitkin County; Silverton in San Juan County; and Telluride in San Miguel County.Colorado's silver mining tradition dates back to 1864, when its first silver lode was discovered "on Glacier Mountain, about a mile south of Montezuma" (Lovering and Goddard, 1950).Interestingly, samples from this district were the catalysts for this investigation.The samples are examples of high grade silver mineralization, but they were unusual for two other reasons.First, they contain microscopic arborescent growths.Second, the fine growths were not noticed until a decade after they were collected.In fact, it is believed that they have formed since they were collected, similar to some polished sections studied from Creede (Raines, pers.comm.2000; Plumlee, pers.comm.2000) and elsewhere (Mozgova et al., 1994).
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