X-RAY MICROPROBE ANALYSIS OF IRON OXIDATION-STATES IN SILICATES AND OXIDES USING X-RAY-ABSORPTION NEAR-EDGE STRUCTURE (XANES)

Initial results are reported on a new microprobe technique for determining Fe3+/SIGMAFe ratios in Fe-bearing minerals. The technique is based on the energy shift of a pre-edge peak in X-ray absorption near-edge structure (XANES) spectra obtained using the synchrotron X-ray fluorescence microprobe. A linear relationship between pre-edge peak energy and iron oxidation state was observed for oxide and silicate standards. Reasonable iron oxidation state results were obtained for pallasitic olivine, acmite, altered magnetites, and synthetic wustite. Direct measurements of Fe3+/SIGMAFe in coexisting phases is feasible using this technique.