Cation distribution in some natural spinels from X-ray diffraction and Mossbauer spectroscopy

Three natural spinels of different places of occurrence and compositions were investigated by means of microprobe chemical analysis, single crystal X-ray diffraction and Mossbauer spectroscopy. All cation distributions between T and M sites were calculated from microprobe and XRD experimental data, by means of a mathematical model with appropriate assumptions. Fe2+ and Fe3+ assignments calculated in this way were compared with those observed in Mossbauer spectra. The satisfactory agreement found proves, at least in the samples studied, the reliability of the model and the assumptions used. In the spinels examined, such results show Fe2+ and Fe3+ virtually ordered in T and M sites respectively. Mossbauer data also revealed Fe2+ in different tetrahedral sites due to the next-nearest neighbour effect, probably as a consequence of spinel genetic conditions.