We have used the technique of scanning force microscopy (SFM) for studying the interaction of the bacteria A. ferrooxidans with the surface of the mineral pyrite. These bacteria are important to study with regard to acidification of streams and the environmental impact of such acidification. A. ferrooxidans cells readily colonize the pyrite surface, forming a tight mineral seal between the cell and the pyrite substrate. These bacteria subsequently may grow under pH neutral conditions, biooxidizing the underlying pyrite; this process creates etch pits in the pyrite. On average, these etch pits are 1.2 microns in lateral dimension and approximately 220 nm deep.