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Infrared powder-absorption spectroscopy of Ca-free P21/c clinopyroxenes

Published online by Cambridge University Press:  05 July 2018

T. Boffa Ballaran ,
M. A. Carpenter  and
N. L. Ross
T. Boffa Ballaran*
Affiliation:
Department of Earth Sciences, Downing St., Cambridge CB2 3EQ, UK
M. A. Carpenter
Affiliation:
Department of Earth Sciences, Downing St., Cambridge CB2 3EQ, UK
N. L. Ross
Affiliation:
Department of Geological Sciences, University College London, Gower St., London WC1E 6BT, UK
*
*E-mail: tiziana.boffa-ballaran@uni-bayreuth.de
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Abstract

Infrared powder-absorption spectra of ten synthetic P21/c pyroxenes with compositions in the clinoenstatite–clinoferrosilite system have been collected at room temperature in the range 50–1500 cm−1. Variations of peak positions as a function of Fe content have been obtained for those vibrational bands whose trend could be followed across the solid solution. Local elastic strains arising from cation substitution have been quantified by means of the autocorrelation function, which gives a measure (Δcorr) proportional to the line width of the IR bands. The structure of clinoenstatite appears to be very homogeneous, whereas Fe-rich pyroxenes have high degrees of local structural hetereogeneities. A positive deviation from linearity of the Δcorr values is observed in the spectral region between 100 and 250 cm−1 and may be indicative of a positive excess enthalpy of mixing of this solid solution. At higher energies the large changes in the phonon spectra as Fe content increases are associated with rotation and deformation of the tetrahedral chains for accommodating the larger cation. The results are compared with similar studies on other chain silicates.

Keywords

P21/c pyroxenesIR spectroscopysolid solution
Type
Research Article
Information
Mineralogical Magazine , Volume 65 , Issue 3 , June 2001 , pp. 339 - 350
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2001

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Footnotes

•

Present address: Bayerisches Geoinstitut, Universität Bayreuth, 95440 Bayreuth, Germany

‡

Present address: Dept. of Geological Sciences, Virginia Tech, Blacksburg, VA 24061, USA

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