Abstract Iron is the third most abundant cation in the Earth's crust and the most abundant redox active constituent. Under some conditions, certain microorganisms can generate energy via catalysis of ferrous iron oxidation. In acidic solutions associated with altered metal sulfide ore deposits, ezymatic iron oxidation leads to increase in metal sulfide dissolution rates and results in an environmental problem known as acid mine drainage. Combination of molecular biological approaches to identify microorganisms and geochemical experiments to quantify rates and products of mineral reactions has advanced our understanding of acid mine drainage formation, as it occurs in Iron Mountain, California .
Iron oxidizing organisms are also present in some near-neutral pH solutions.
Recent microbiological studies suggest that these may be of greater geochemical importance than previously recognized. Research in a flooded mine system in Wisconsin has revealed abundant iron oxidizing miroorganisms in gradients between anoxic Fe-bearing groundwater and oxidized portions of the tunnel system. Due to the low solubility of ferric iron at pH 8, microbial catalysis of iron oxidation leads to precipitation of highly reactive iron ixyhydroxide phases on polymers and in solution and, over about 30 years, has resulted in tens of centimeter thick iron ixyhydroxide-polymer bioaccumulations. They are fundamental to an understanding of the origin of acid mine drainage, a cause of pollution associated with mining, and in the search for means of its control. Biographical Information Jillian Banfield, a mineralogist, has contributed fundamental insights into the physical and chemical forces that shape the earth's surface.