Room-temperature 57Fe Mössbauer spectra of synthetic orthopyroxenes equilibrated between 900–1000 °C and spanning the compositional range from ferrosilite to nearly enstatite were acquired. Peak areas corresponding to Fe2+ in the M1 and M2 sites of the structure were corrected for effects of thickness and differential recoil-free fractions (f) on the two sites using a constant value of C = 1.1, the correction parameter. The distribution coefficient, KD, for Fe and Mg in M1 and M2 was calculated for all samples, and results were compared to KD values from previous studies where C was assumed to be unity. Our results demonstrate that choice of C dramatically influences calculated KD values. Thus, the failure of previous studies to consider C corrections may well be responsible for differences between Mössbauer and XRD studies of site occupancies noted by previous workers. Further characterizations of f for pyroxenes of variable compositions are needed.

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