Well characterized, an Egyptian coal sample (EM-87) has been carbonized in an Argon atmosphere of pressure 10(5) Pa at different temperatures from 700-1000 K. The analysis of the Mossbauer spectra collected at room temperature for the produced semi-cokes, showed that pyrite FeS2 was starting to be transformed to pyrrhotite Fe1-xS at 700 K. This transformation was found to be increased when the pyrolysis temperature was increased.