Formation of copper—iron sulfide minerals during corrosion of artifacts and possible implications for pseudogilding

Adherent films of the gold-colored metal sulfides pyrite (FeS₂), pyrrhotite (Fe_1−xS), and chalcopyrite (CuFeS₂) are known to exist on metallic and nonmetallic artifacts of Classic times. Consideration of the action of bacterial consortia containing sulfate reducing bacteria (SRB) during microbiologically influenced corrosion (MIC) and analyses of appropriate trajectories on Eh-pH stability diagrams indicate that these films can be understood either as a result of natural processes over archaeological times or of deliberate pseudogilding. Methods of discriminating natural sulfide deposition from pseudogilding are suggested. © 1993 John Wiley & Sons, Inc.