M?ssbauer Assessment of Cation Disorder in Columbite-Tantalite Minerals

We have used X-ray diffraction and M?ssbauer spectroscopy to investigate the cationic disorder between crystallographic sites of a columbite-tantalite series of pegmatites. The X-ray results show that the pegmatites have different degrees of crystallographic disorder according to the quarries where the samples come from. M?ssbauer spectra allow us to distinguish two Fe2+different sites. A simple model assuming equalf-factors and occupation probabilities both for Fe and Mn has been used to turn the relative populations for Fe yielded by M?ssbauer spectroscopy into effective site occupancy of the 2+ ions. A well-known empirical formula applied to X-ray results to obtain cationic disorder has been found to correlate within experimental errors with the percentage of cationic ordering obtained by M?ssbauer spectroscopy.