Measurement of Fe3+/Fe2+ratios in basaltic class I titanomagnetites using the Mössbauer Effect

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Mössbauer spectroscopy has been used to measure Fe3+/Fe2+ ratios in basaltic class I titanomagnetites. Analyses were carried out at 87°K because the lines in the Mössbauer spectrum were better resolved at low temperatures. The spectra were fitted, using a least-squares technique, to two magnetic hyperfine fields, one a sharply defined ferric field, and the other a ferrous field with broad lines due to local inhomogeneities producing a range of ferrous hyperfine fields. The Fe3+/Fe2+ ratios were calculated from the absorption areas of the two fields, with the two recoil-free fractions taken to be equal. Four low Curie temperature samples (150°–300°C) yielded Fe3+/Fe2+ ratios between 0.8 and 0.9, while two high Curie point specimens (550°–600°C) had ratios between 1.1 and 2.0. The higher Curie point samples had Mössbauer parameters very similar to those of natural magnetite at 87°K.