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Infrared spectra of synthetic almandine–grossular and almandine–pyrope garnet solid solutions: evidence for equivalent site behaviour

Published online by Cambridge University Press:  05 July 2018

C. A. Geiger ,
B. Winkler  and
K. Langer
C. A. Geiger
Affiliation:
Institut für Mineralogie und Kristallographie, Technische Universität Berlin, Ernst Reuter-Platz 1, D-1000 Berlin 12, Germany
B. Winkler
Affiliation:
Institut für Mineralogie und Kristallographie, Technische Universität Berlin, Ernst Reuter-Platz 1, D-1000 Berlin 12, Germany
K. Langer
Affiliation:
Institut für Mineralogie und Kristallographie, Technische Universität Berlin, Ernst Reuter-Platz 1, D-1000 Berlin 12, Germany
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Abstract

The infrared (IR) spectra of almandine-grossular and almandine-pyrope garnet solid solutions have been measured using the powder method. Frequency shifts of a band related to internal vibrations associated with the 8-co-ordinate dodecahedral site are nonlinear in almandine-grossular garnets and mimic the form of its molar volume of mixing curve. Almandine-pyrope solid solutions have nearly ideal molar volumes of mixing and the frequency shift of this same 8-co-ordinate site-related band is linear. The IR data support the empirically based crystal chemical model of Equivalent Site (ES) behaviour (Newton and Wood, 1980). The IR spectra give no indication of long-range ordering between Ca and Fe2+ in garnet, but thermodynamic calculations involving Ca-poor garnets might be affected by small volume or short-range ordering anomalies.

Keywords

equivalent site behavioursynthetic garnetsinfrared spectroscopymolar volumes of mixing
Type
Research Article
Information
Mineralogical Magazine , Volume 53 , Issue 370 , April 1989 , pp. 231 - 237
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1989

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