Hyperfine Splitting of Fe⁵⁷ and Mg-Fe Order-Disorder in Orthopyroxenes (MgSiO₃-FeSiO₃ Solid Solution)

Abstract

The apparent "two-line" hyperfine spectrum of Fe57 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 Fe2+ sites, M1 and M2, of the crystal structure. The approximated intrinsic values of the electric quadrupole interaction \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage{wasysym} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document}$$\frac{1}{2} |e^{2}qQ| (1 + [\eta^{2}/3])^{1/2}$$\end{document} and isomer shifts at M1 and M2 are: The Fe2+ 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.