Acid mine drainage (AMD) is the result of exposure of sulfidic seams to the oxidizing and leaching action of water—rain water, humidity, and groundwater— and is exacerbated by microorganisms that catalyze the solubilization of sulfide minerals by the regeneration of Fe3+ and oxidation of their dissolution products as the source of energy. Typical AMD has a low pH and a high sulfate and ferric iron concentration although other metals may also be present. The chemical composition of AMD varies with sulfide minerals associated with coal and metal mines. At low pH, ferric iron in AMD participates in the leaching action, as shown for pyrite (FeS2) and chalcopyrite (CuFeS2).