Sulphur Formation by the Action of Bacteria.—The sulphur bacteria (purple bacteria, Beggiatoa, Thiothrix, Thiovolum, Thiophysa spp., etc.) which oxidize hydrogen sulphide are widely distributed in nature. Their communities live chiefly in sulphur springs and on the shores of brackish waters. The sulphuric acid resulting from oxidation of H2S is neutralized by carbonates (mostly CaCO3): (H2SO4 + CaCO3 = CaSO4 + CO2 + H2O) and deposited as sulphate, in this case as calcium sulphate. (Braun-Blanquet 1932:203)
BRAUN-BLANQUET, Josias. 1932. Plant sociology: the study of plant communities. (Trans.: George D. Fuller; Henry S. Conard) New York: McGraw-Hill Book Company.