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Gems & Gemology, Fall 1988, Vol. 24, No. 3
A Gem-Quality Iridescent Orthoamphibole from Wyoming
R. V. Dietrich, John Sampson White, and Joseph E. Nelen, Kwo-Ling Chyj
A gem-quality iridescent orthoamphibole from Wyoming, similar to that described from Greenland, has been identified. This ornamental material occurs in a weathered gneiss-schist, near its contact with a peridotite mass. Most of the individual iridescent grains that constitute this rock are golden or dark brown, but a few are rose red or silvery gray. They consist principally of goethite and/or opaline silica, which probably was derived directly from the original ferroanthophyllite as a result of weathering. Economic amounts of this material are not available at this time, although it is likely that the deposit has the potential to produce significant quantities.
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