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The crystal structure and chemistry of high-aluminium phlogopite

Published online by Cambridge University Press:  05 July 2018

Elisa Alietti ,
Maria Franca Brigatti  and
Luciano Poppi
Elisa Alietti
Affiliation:
Dipartimento di Scienze della Terra, Università di Modena, Via S. Eufemia 19, I-41100 Modena, Italy
Maria Franca Brigatti
Affiliation:
Dipartimento di Scienze della Terra, Università di Modena, Via S. Eufemia 19, I-41100 Modena, Italy
Luciano Poppi
Affiliation:
Dipartimento di Scienze della Terra, Università di Modena, Via S. Eufemia 19, I-41100 Modena, Italy
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Abstract

Crystal structure refinements were performed on five Al-rich phlogopite-1M crystals (1.50 ⩽ Al3+ ⩽ 1.97 atoms per formula unit) from skarns of the Predazzo and Monzoni Hills petrographic area (north-east Italy) with the aim of characterizing geometrical variation produced by Al3+ increase. The charge imbalance was mostly compensated for by substitutions of highly charged cations in the octahedral sheet (Al3+ and/or Fe3+ for Mg2+). The refinements were carried out in the mean space group C2/m and gave agreement values (R) between 0.025 and 0.030. For some additional crystals, only chemistry and/or unit cell parameters were determined. In all samples the tetrahedra are more regular and larger than those previously reported in the literature for phlogopite crystals and the misfit between tetrahedral and octahedral sheets, produced by the increase in the tetrahedral edges, is mostly compensated for by the tetrahedral ring angle rotation α (10.2 °⩽ α ⩽ 12.5°), whereas the octahedral sheet features seem affected only by local crystal-chemical variations.

Keywords

Al-rich phlogopiteclintonitecrystal chemistrystructure refinementskarns
Type
Mineralogy
Information
Mineralogical Magazine , Volume 59 , Issue 394 , March 1995 , pp. 149 - 157
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1995

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