Original paper

Iron distribution in orthopyroxene: A comparison of Mössbauer spectroscopy and X-ray refinement results

Skogby, Henrik; Annersten, Hans; Domeneghetti, Maria Chiara; Molin, Gian Mario; Tazzoli, Vittorio

European Journal of Mineralogy Volume 4 Number 3 (1992), p. 441 - 452

23 references

published: Jun 11, 1992
manuscript accepted: Oct 16, 1991
manuscript received: Mar 12, 1991

DOI: 10.1127/ejm/4/3/0441

BibTeX file

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Abstract The Fe-Mg distribution over the Ml and M2 octahedral sites in five natural orthopyroxenes has been determined by single-crystal X-ray diffraction (XRD) and Mössbauer spectroscopy (MS). The results from the two methods are in good agreement for two Fe/Mg intermediate composition samples, provided that the MS data are thickness-corrected. For two Fe-poor and one Al-rich sample, the results diverge ; XRD gives a more ordered Fe-Mg distribution than MS, with up to 0.05 more Fe atoms per formula unit in the M2 position. The thickness effect on MS for ordered orthopyroxene is shown to cause considerable distortion of the spectra, resulting in an underestimate of the degree of ordering. For normally thick absorbers (5 mg Fe/cm2), MS data will allocate approximately 2% too much of total Fe to the Ml position. However, the Fe distribution obtained from MS data can be corrected by extrapolation to zero thickness according to the formula Fe(Ml)/Fe(tot)corr = [Fe(Ml)/Fe(tot)meas - 0.004085t]/(l - 0.003031t), where t is the Fe « thickness » of the absorber in mg Fe/cm2


X-ray diffractionMössbauer spectroscopythickness effectorthopyroxeneorder-disorder