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Hyperfine Splitting of $Fe^{57}$ and Mg-Fe Order-Disorder in Orthopyroxenes ($MgSiO_{3}-FeSiO_{3}$ Solid Solution)

B. J. Evans, Subrata Ghose and Stefan Hafner
The Journal of Geology
Vol. 75, No. 3 (May, 1967), pp. 306-322
Stable URL: http://www.jstor.org/stable/30071517
Page Count: 17
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Hyperfine Splitting of $Fe^{57}$ and Mg-Fe Order-Disorder in Orthopyroxenes ($MgSiO_{3}-FeSiO_{3}$ Solid Solution)
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Abstract

The apparent "two-line" hyperfine spectrum of $Fe^{57}$ in some orthopyroxene minerals from metamorphic rocks has been analyzed by the Mössbauer technique. The spectrum consists predominantly of two overlapping two-line patterns. The patterns have been assigned to the two non-equivalent $Fe^{2+} sites, M_{1}$ and $M_{2}$, of the crystal structure. The approximated intrinsic values of the electric quadrupole interaction $\frac{1}{2} \mid e^{2}qQ \mid (1 + [\eta^{2}/3])^{1/2}$ and isomer shifts at $M_{1}$ and $M_{2}$ are: The $Fe^{2+}$ site occupancies have been approximately determined. The high degree of Mg-Fe ordering in an orthopyroxene (Fe/[Mg + Fe] = 0.535) found previously by X-ray diffraction has been confirmed. Heat treatment of this sample at 1,000° C. and 1,100° C. yields considerable Mg-Fe disorder.

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