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Incorporation of REE into leucophanite: a compositional and structural study

Published online by Cambridge University Press:  05 July 2018

H. Friis ,
T. Balić-Žunić ,
C. T. Williams  and
R. Garcia-Sanchez
H. Friis*
Affiliation:
Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10, 1350 København K, Denmark
T. Balić-Žunić
Affiliation:
Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10, 1350 København K, Denmark
C. T. Williams
Affiliation:
Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10, 1350 København K, Denmark
R. Garcia-Sanchez
Affiliation:
Department of Mineralogy, Natural History Museum, Cromwell Road, London, SW7 5BD, UK
*
E-mail: geofriis@yahoo.com
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Abstract

The crystal structures of nine, and the chemical compositions of ten, natural samples of leucophanite, ideally NaCaBeSi2O6F, were investigated. The analysed samples display a large compositional variation with trace-element abundances >50,000 ppm, primarily due to rare earth elements (REE). Fromthese data, we propose a substitution scheme for the incorporation of REE for Ca, with additional Na substituting for Ca and the generation of vacancies to ensure charge balance. Compositional zonation was observed in some samples; this zonation correlates with variations in cathodoluminescence. The crystal structure of the nine analysed samples could all be refined in space group P212121. We found no evidence for a reduction of symmetry with increased trace-element concentration. Various twin combinations were observed and these seem related to crystallization conditions rather than structural or chemical factors.

Keywords

leucophaniteREEcrystal-chemistryalkaline complexescrystal twins
Type
Research Article
Information
Mineralogical Magazine , Volume 71 , Issue 6 , December 2007 , pp. 625 - 640
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2007

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Footnotes

†

Present address: School of Geography and Geosciences, University of St Andrews, Irvine Building, North Street, St Andrews, Fife, KY16 9AL, UK

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