Iron sulfide production by bacteria can be classified as extracellular or intracellular. Extracellular iron sulfide production is mediated by anaerobic, dissimilatory sulfate-reducing bacteria which produce sulfide as a product of their respiration. Released sulfide reacts with iron (and other metals) in the extracellular environment producing a variety of iron sulfide minerals including “amorphous iron sulfide”, mackinawite, greigite, pyrrhotite, marcasite, and pyrite. The type of minerals formed is dependent upon pH, Eh, and other physical and chemical factors. Extracellular production of these minerals are examples of biologically-induced mineralization in which mineral formation occurs from chemical and/or physical changes in the surrounding environment by the organism.