X-ray diffraction and Mössbauer spectroscopy at room and liquid-N2 temperatures have been used to examine the Fe distribution in a staurolite with an approximate composition of


The space group is C2/m, and lattice parameters at room and low temperatures, respectively, are a = 7.865(2) and 7.871(2) Å, b = 16.580(4) and 16.587(5) Å, c = 5.668(3) and 5.661(3) Å, and β = 90.38(5)° and 90.39(7)°. Optical properties measured for this staurolite are α = 1.738(2), β 1.743(2), γ = 1.747(2), and 2VX = 89.5(7)°. The Mössbauer spectra are fit to four doublets, resulting in x2 values of 1.2 and 1.3 for the room- and low- temperature spectra, respectively. The room- and low-temperature structure refinements resulted in R values of 0.031 and 0.032, respectively.

The following distribution of Fe is derived solely from structure-refinement results: 92% in [4]Fe, 6% in [6]Al(3), and 2% in [6]U. Mössbauer spectra indicate that 5-10% of the Fe is trivalent. The three largest Mössbauer doublets are attributed to Fe2+ in energetically nonequivalent [4]Fe sites. Positional disorder at the Fe site is attributed to variations in the crystal-field energy at the Fe site. Intensities of the Mössbauer doublets and of the electron-density peaks at the Fe site exhibit no definite temperature dependence.

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