Local structure of ferric iron-bearing garnets deduced by IR-spectroscopy |
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| Institution: | 1. Bayerisches Geoinstitut, Universität Bayreuth, D-95440 Bayreuth, Germany;2. Institut für Mineralogie, Johann Wolfang Goethe-Universität, Senckenberganlage 30, D-60054 Frankfurt am Main, Germany;1. Department of Earth and Marine Sciences, University of Palermo, Via Archirafi 36, 90123 Palermo, Italy;2. Department of Physics and Earth Sciences, University of Ferrara, Via Saragat 1, 44122 Ferrara, Italy;3. Consiglio Nazionale delle Ricerche, CNR-IDPA, Section of Milan, Via Mangiagalli 34, 20133 Milan, Italy;4. Department of Earth Sciences “A. Desio”, University of Milan, Via Botticelli 23, 20133 Milan, Italy;1. Institut de Physique du Globe de Paris, Sorbonne Paris Cité, 75005 Paris, France;2. School of Earth and Space Exploration, Arizona State University, 781 S. Terrace Road, Tempe, AZ 85281, USA;3. École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland;1. University of Toronto, Department of Earth Sciences, 22 Russell Street, Toronto, Ontario, M5S 3B1, Canada;2. Department of Earth Sciences, University of Minnesota, Minneapolis, MN 55455, United States;3. Minnesota Supercomputing Institute, Minneapolis, MN 55455, United States;4. School of Environmental Studies, China University of Geosciences, Wuhan, 430074, China;1. Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501, Japan;2. Institute for Research on Earth Evolution (IFREE), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Natsu-shima, Yokosuka 237-0061, Japan;3. Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo 152-8551, Japan;4. Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo 152-8551, Japan;5. Japan Synchrotron Radiation Research Institute, Sayo 679-5198, Japan;1. The City College of New York, CUNY, 160 Convent Ave, New York, NY, USA;2. The Graduate Center of the City University of New York, 365 Fifth Avenue, New York, NY, 10016, USA;3. Dpto. de Quimica Inorganica, Universidad de Malaga, Spain |
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| Abstract: | Powder IR absorption spectroscopy has been used to characterise cation substitutions in three garnet solid solutions: grossular–andradite, skiagite–andradite and skiagite–almandine. The wavenumber shift of the highest energy mode associated with tetrahedral vibrations depends on the type of cation occupying the adjacent sites in the structure. The wavenumber shifts exhibit positive deviations from linearity that correlate closely with the variations of the Si–O bond distances for all three garnet solid solutions. The autocorrelation function has been used to determine an effective line width (Δcorr) of the absorption bands over a given spectral region. Non-linear behaviour of Δcorr was found for all three solid solutions. An empirical calibration between Δcorr excess and calorimetric enthalpy of mixing data gives an estimate for the symmetric Margules parameters WspecH of the three solid solutions. Comparison with the systematics of aluminosilicate garnets in terms of WspecH vs. ΔV2, where ΔV represents the difference in molar volume between the end members in a binary system, reveals that such a relationship is not generally applicable to garnet solid solutions with an octahedral cation other than Al. |
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