On Mössbauer analysis of mineral mixtures having environmentally broadened spectral lines. Application to bauxite

Careful analysis of bauxite Mössbauer spectra reveals non-Lorentzian spectral line broadening, which is shown to be due to environmental rather than thickness effects. Similar broadening is often observed in published mineral Mössbauer spectra, and it is demonstrated here that the pseudo-Lorentzian line shape is useful for fitting such environmentally broadened spectra. Using simulated spectra, it is shown that the effects of major-component spectral lines on the fitted parameters of poorly resolved minor components may be considerable, particularly in the presence of asymmetric environmental line broadening. In the particular case of bauxite, such effects occur due to the influence of the dominant hematite sub spectrum on the minor goethite sub spectrum. For bauxite spectra having <50% goethite relative spectral area it is necessary to constrain goethite line width and intensity ratios during fitting in order to extract useful information.