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A combined temperature dependent57Fe Mössbauer and single crystal X-ray diffraction study of synthetic almandine: evidence for the Gol'danskii-Karyagin effect |
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| Authors: | C A Geiger Th Armbruster G A Lager K Jiang W Lottermoser G Amthauer |
| Institution: | 1. Bayerisches Geoinstitut, Universit?t Bayreuth, W-8580, Bayreuth, Federal Republic of Germany 3. Laboratorium für chemische und mineralogische Kristallographie, Universit?t Bern, Freiestrasse 3, CH-3012, Bern, Switzerland 4. Department of Geology, University of Louisville, 40292, Louisville, KY, USA 5. Institut für Mineralogie, Universit?t Salzburg, A-5020, Salzburg, Austria |
| Abstract: | Synthetic almandine garnet, Fe3Al2Si3O12, has been studied by temperature — dependent single crystal X-ray diffraction and57Fe Mössbauer spectroscopy. The Fe2+ doublet in almandine is characterized by a small asymmetry between the high and low-velocity peaks that decreases in magnitude with decreasing temperature from 420 to 15 K. The X-ray results show that the Fe2+ cation is dynamically disordered with an anisotropic motion within the eight-coordinated site in garnet. The magnitudes of the X-ray determined mean-square-vibrational amplitudes of this motion parallel,x ∥, and perpendicular,x ⊥, to the principle axes of the electric field gradient give a calculated angular dependence of the electric quadrupole interaction of theI 1/2 toI 3/2 transitions that agree with the experimentally measured peak ratios. This is the first recognition of anisotropic recoil free fraction of57Fe in silicates. |
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