Widespread occurrence of a novel high coercivity, thermally stable, low unblocking temperature magnetic phase in heated archeological material

The widespread occurrence of a novel, high coercivity magnetic phase in well- heated archeological material is reported. Its properties are defined when it represents the dominant magnetic phase, although it is nearly always found as part of a mixture of magnetic phases. They are as follows: very high coercivity ( remanence coercivity > 600 mT), low unblocking temperatures (<= 200 degrees C) and high degree of thermal stability - this last property distinguishing it from goethite. The phase shows striking similarities to magnetic phases produced by thermal decomposition of nontronite ( an Fe- rich clay), where decomposition occurs after prolonged heating in air to high temperatures - conditions suffered by well- heated archeomagnetic material. Preliminary results of Mossbauer and X- Ray diffraction spectroscopy suggest that the phase is more likely to be a substituted hematite, rather than Fe-cristobalite or a variant of epsilon- Fe2O3.