text: The water gas shift reaction (CO + HO → CO + H) occurs in volcanic fluids with diverse catalysts or without catalysts.  The combination of ferrous sulfide (FeS, troilite) and hydrogen sulfide () as reducing agents (both reagents are simultaneously oxidized in the reaction here under creating the disulfide bond, S–S) in conjunction with pyrite () formation: 
  : FeS + HS → FeS + 2 H + 2 e
  : or with H directly produced instead of 2 H + 2 e
  : FeS + HS → FeS + H
  has been demonstrated under mild volcanic conditions.  This key result has been disputed. Nitrogen fixation has been demonstrated for the isotope N in conjunction with pyrite formation. Ammonia forms from nitrate with FeS/HS as reductant. Methylmercaptan [CH-SH] and carbon oxysulfide [COS] form from CO and FeS/HS, or from CO and H in the presence of NiS.