The unexpected observation that the common mineral iron sulfide FeS2 produces CS2 and OCS when incubated with water has been further investigated by testing either untreated pyrite or pyrite cleaned with acid and an organic solvent. OCS and CS2 were produced in all experiments except those excluding oxygen or those thoroughly cleaned with acetonitrile. These results indicate that both oxygenated water and organic matter are needed to produce OCS and CS2. Oxygenated groundwater with dissolved organic matter is widespread in most geologic environments, as are metal surfides, suggesting that oxidative decomposition of pyrite should be investigated as a source of OCS and CS2 to the atmosphere.