CATION DISTRIBUTION IN SOME NATURAL SPINELS FROM X-RAY-DIFFRACTION AND MOSSBAUER-SPECTROSCOPY

Three natural spinels of different places of occurrence and compositio ns were investigated by means of microprobe chemical analysis, single crystal X-ray diffraction and Mossbauer spectroscopy. All cation distr ibutions 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 com pared with those observed in Mossbauer spectra. The satisfactory agree ment found proves, at least in the samples studied, the reliability of the model and the assumptions used. In the spinels examined, such res ults show Fe2+ and Fe3+ virtually ordered in T and M sites respectivel y. Mossbauer data also revealed Fe2+ in different tetrahedral sites du e to the next-nearest neighbour effect, probably as a consequence of s pinel genetic conditions.