Iron oxidation state and local structure in North American tektites

The iron oxidation state and coordination number have been determined by Fe K-edge X-ray absorption-near edge spectroscopy (XANES) for six tektites from the North American tektite strewn field (four bediasites and two georgiaites) and a tektite fragment from the Deep Sea Drilling Project (DSDP) Site 612, which is part of the North American tektite strewn field. All tektite samples display a pre-edge peak, the components of which are consistent with the presence of divalent Fe. Comparison of pre-edge peak data (integrated intensity and centroid energy) with those of Fe model compounds allows us to quantitatively determine the Fe oxidation state and coordination number. The Fe3+/(Fe 2+ + Fe3+) ratio is close to 0.05 (±0.03), consistent with tektites from all the other strewn fields. The average Fe coordination number is intermediate between 4 and 5. Accurate determination of this value is hindered by the scatter of pre-edge peak intensity of all the Fe model compounds; [4]Fe/([4]Fe +[5]Fe) is estimated to be 0.26 ± 0.15. In contrast to North American microtektites, for which iron oxidation state and coordination numbers display significant variations across the North American strewn field, no significant variations in the Fe oxidation state and coordination number were found between the georgiaites, bediasites, and the DSDP 612 tektite fragment. It is remarkable that the tektite fragment from the DSDP 612 site showed no sign of oxidation despite the long burial period in marine sediments.