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o Hydrothermal (epithermal) environment. (chapter 12) - High grade silver-gold ore from the Comstock Lode, Virginia City, Nevada. Well-formed pyrite (white with several crystal faces), quartz far right and lower left (black) was followed by intergranular crystallization of chalcopyrite (dull yellow, far right), acanthite (gray) and gold (golden yellow, central area). The softness of acanthite and gold is indicated by a high density of scratches acquired during preparation of the polished section. Reflected light. View width is 0.5 mm. Specimen provided by the Smithsonian Institute. 
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