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Physics and Chemistry of Minerals

, Volume 27, Issue 9, pp 645–649 | Cite as

Low-temperature single-crystal Raman spectrum of pyrope

  • B. A. Kolesov
  • C. A. Geiger
ORIGINAL PAPER

Abstract

 The single-crystal polarized Raman spectra of synthetic pyrope, Mg3Al2Si3O12, were measured at room temperature and 5 K, as were the room-temperature unpolarized spectra of two natural pyrope-rich crystals. No major differences in the spectra between room temperature and 5 K are observed or are present between the synthetic and the natural crystals. The spectra are consistent with the proposal that the Mg cation is dynamically disordered and not statically distributed over subsites in the large triangular-dodecahedral E-site in pyrope. A low-energy band at about 135 cm−1 softens and shows a large decrease in its line width with decreasing temperature. The presence of a weak, broad band at about 280 cm−1 may be due to anharmonic effects, as could the one at 135 cm−1. The latter is assigned to the rattling motion of Mg in pyrope in the plane of the longer Mg-O(4) bonds (Kolesov and Geiger 1998). The successful modeling of the anisotropic motion of the Mg cation in pyrope, which has an anharmonic character, provides a valuable test of the validity of empirical or semi-empirical lattice-dynamic calculations for silicates.

Key words Pyrope Raman spectroscopy Dynamic cation disorder Anharmonicity 

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Copyright information

© Springer-Verlag Berlin Heidelberg 2000

Authors and Affiliations

  • B. A. Kolesov
    • 1
  • C. A. Geiger
    • 2
  1. 1.Institute of Inorganic Chemistry, Lavrentiev prosp. 3, Novosibirsk 630090, RussiaRU
  2. 2.Institut für Geowissenschaften der Universität Kiel, Olshausenstr. 40, 24098 Kiel, Germany e-mail: NMP46@rz.uni-kiel.de Tel.: +49-431-8802895; Fax: +49-431-8804457DE

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