MICROANALYSIS OF IRON OXIDATION-STATES IN EARTH AND PLANETARY MATERIALS

Initial studies have been made on quantifying Fe oxidation states in different iron-bearing minerals using K-edge XANES. The energy of a weak pre-edge peak in the XANES spectrum due to 1s-3d electron transition was used to quantify ferric/ferrous ratios with microprobe spatial resolution. The estimated accuracy of the technique was +/- 10% in terms of Fe3+/(Fe2+ + Fe3+). The detection limit was similar to 100 ppm with a synchrotron beam of similar to 100 mu m in diameter. The pre-edge peak energy in well-characterized samples with known Fe oxidation states was found to be a linear function of the ferric/ferrous ratio. The technique was applied to altered magnetites (ideally Fe3O4), and various silicates and oxides from meteorites.