AsymplectiteofpyriteandmagnetiteinthemassivesulphideoreoftheMashanmine,AnhuiProvince,isinterpretedtohavebeenformedbytheirreplacingearlierpyrrhotite.Thecompositionsofpyrrhotite,pyriteandmagnetiterelatedtothistexturearegivenbyelectronmicroprobeanalysis.Suchatextureislikelytobeformedwhentheore-formingsystemreachesthethree-phasepointofpyrrhotite,pyriteandmagnetitefromthepyrrhotitestabilityfield.Theverysmallprobabilityforthesystemtoreachthispointcouldbeusedtoaccountfortherareoccurrenceofsuchsymplectiteinnaturalores.