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 determi ning Fe3+/SIGMAFe ratios in Fe-bearing minerals. The technique is base d on the energy shift of a pre-edge peak in X-ray absorption near-edge structure (XANES) spectra obtained using the synchrotron X-ray fluore scence 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 me asurements of Fe3+/SIGMAFe in coexisting phases is feasible using this technique.