Backscattering Mössbauer MIMOS II and XRF studies on tektites from different strewn fields

Abstract

Room temperature ⁵⁷Fe Mössbauer spectroscopy has been used to obtain information on the redox and coordination of iron in tektites. A MIMOS II spectrometer in backscattering geometry has been used in the study, so that no sample preparation at all was required. X-ray fluorescence has been used to determine the composition of the tektites. Mössbauer spectra have been deconvoluted using three extended Voigt-based profiles to allow quantitative analysis of iron atoms valence and coordination. In all tektites, the Fe$^{2+ }$sites have been distinguished in Fe with octahedral and tetrahedral coordination. The Fe$^{2+}$octahedral sites show a region of isomer shift (IS) and quadrupole splitting (QS), IS $=$ 1.02–1.14 mm/s and QS $=$ 1.82–2.12 mm/s, relative to $\alpha$-Fe. The Fe$^{2+ }$tetrahedral sites show a region of hyperfine parameters of IS = 0.59–0.89 mm/s and QS = 1.14–1.60 mm/s. The Fe³⁺sites show IS = 0.11–0.33 mm/s and QS = 0.02–0.04 mm/s. The Fe³⁺/Fe²⁺ ratio was found to be 0.025–0.149.