Selected pyrite crystals were placed as a bacterial energy source into stationary cultures of Thiobacillus ferroxidans. Scanning electron microscope studies performed after a period of 2 years on these crystals revealed bacterial etching pits in characteristic patterns; they include pit arrangements in loose statistical disorder, in pairs, in clusters, and most remarkably in pearl-string-like chains. It has previously been confirmed that the chemical processes of bacterial leaching occur mainly in the region of contact between bacteria and the sulfide surface. The evidence presented in this experiment strongly suggests that the observed bacterial distributions are critically dependent on crystal structure and on deviations in the crystal order (fracture lines, dislocations) of the leachable substrate.