Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Sulfur is one of the constituents of many proteins, vitamins and hormones. It recycles as in other biogeochemical cycles. The essential steps of the sulfur cycle are: Mineralization of organic sulfur to the inorganic form, hydrogen sulfide: (H2S). Oxidation of sulfide and elemental sulfur (S) and related compounds to sulfate (SO42 ). Reduction of sulfate to sulfide. Microbial immobilization of the sulfur compounds and subsequent incorporation into the organic form of sulfur.