The metallic and silicate phases of a saussuritized quartz diorite were examined after 21 months of microbiological leaching. Essentially all the chalcocite and malachite disappeared. The chalcopyrite was not completely oxidized, but the mineral surfaces were discolored and etched. The molybdenite was unetched. The most abundant sulfide mineral present, was pyrite which was tarnished a deep yellow and heavily etched (Swiss cheese appearance). This etching suggests direct microbiological attack. Model experiments using pyrite from the same source confirmed that the etching only occurred when Thiobacillus ferrooxidans was present.

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