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The significance of the aluminium content of a lizardite at the nanoscale: the role of clinochlore as an aluminium sink

Published online by Cambridge University Press:  05 July 2018

G. Cressey ,
B. A. Cressey  and
F. J. Wicks
G. Cressey*
Affiliation:
Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
B. A. Cressey
Affiliation:
Electron Microscopy Centre, School of Chemistry, University of Southampton, Southampton SO17 1BJ, UK
F. J. Wicks
Affiliation:
Natural History Department, Royal Ontario Museum, 100 Queen’s Park, Toronto M5S 2C6, Canada
*
*E-mail: g.cressey@nhm.ac.uk
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Abstract

Lizardite-1T crystals from Gew-graze at the Lizard, Cornwall, of an apparent composition (Mg2.94Fe0.03Al0.03)(Si1.97Al0.03)05(OH)4, have been observed to contain 2–5% of thin interstratifications of clinochlore when investigated by analytical transmission electron microscopy (TEM). The clinochlore is usually only a few unit layers thick but has an extensive lateral dimension parallel to the lizardite layers. Analytical TEM confirms the existence of very low-Al lizardite with a planar structure interstratified with occasional thin units of clinochlore containing substantial Al. Compositionally, such clinochlore (invisible by X-ray diffraction) interstratified throughout the lizardite crystals, could account for most of the Al present. We suggest that an occasional influx of Al causes the nucleation and growth of clinochlore at the expense of lizardite. The possibility of clinochlore contributing to the measured Al content in lizardite samples highlights the need for future investigations of Al-bearing serpentines to include careful examination and interpretation using imaging and analysis by TEM.

It has crept into serpentine discussions that lizardite cannot form without the coupled substitution of Al to relieve the misfit between the sheets of octahedra and tetrahedra. The lizardite at Gew-graze is almost Al-free, forms well-crystallized planar crystals and demonstrates that Al is not an essential element for lizardite crystallization.

Keywords

lizarditeclinochlorealuminiumelectron microscopyanalytical electron microscopyLizard PeninsulaCornwallEngland
Type
Research Article
Information
Mineralogical Magazine , Volume 72 , Issue 3 , June 2008 , pp. 817 - 825
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2008

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