Magnetic hyperfine fields in ferrigehlenites

Western Canadian cretaceous coal (WC5) and Appalachian carboniferous coal (AC4) are good coking coals, although their rheological properties predict a different behaviour with this respect. According to Mössbauer Spectroscopy, iron-based mineral matters of these coals are very different: WC5 spectrum exhibits chiefly Fe₃O₄ while AC4 contains mainly ferrous silicate and no ferric ion. However the spectra of the ashes exhibit a similarity: they characterize α-Fe₂O₃ with a distribution of particle sizes extended down to some tens of nanometers. Such a dispersion could favour catalytic processes during the low temperature stages of coking.