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Dehydroxylation of Fe3+ , Mg-rich dioctahedral micas: (II) cation migration

Published online by Cambridge University Press:  09 July 2018

F. Muller ,
V. A. Drits ,
S. I . Tsipursky  and
A. Plançon
F. Muller*
Affiliation:
ISTO, University of Orléans, CNRS, 1A, rue de la Férollerie, 45071 Orléans, Cedex 2, France
V. A. Drits
Affiliation:
Geological Institute of the Russian Academy of Sciences, Pyzhevsky per. 7, MoscowRussia
S. I . Tsipursky
Affiliation:
Geological Institute of the Russian Academy of Sciences, Pyzhevsky per. 7, MoscowRussia
A. Plançon
Affiliation:
ISTO, University of Orléans, CNRS, 1A, rue de la Férollerie, 45071 Orléans, Cedex 2, France
*
*E-mail: fabrice.muller@univ-orleans.fr
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Abstract

The quantitative interpretation of the reflection intensities of the SAED patterns of glauconites reveals the mechanism of migration of the octahedral sheet cations during heating up to 750°C. It confirms that Mg2+ has a greater ability than Fe3+ to migrate from cis-to trans-sites, as previously found by means of XRD pattern modelling. For samples heated to 650°C, the two formerly vacant trans-sites in the base-centred unit-cell become occupied, but differently, which leads to a primitive unit-cell, and the cis-sites remain filled almost entirely by Fe3+ only. The cation migration occurs through the nearest shared edges in the [010] and [310] directions. The samples heated to 750°C reveal a base-centred super-cell with A = 3a and B = b. All Mg cations leave the cis-sites to occupy completely four of the six available trans-sites of the super-cell. Migration also occurs through the shared edges in the [010] and [310] directions. The primitive unit-cell is not an intermediate step in the migration process leading to the super-cell. The existence of additional satellites in the SAED patterns of some crystals heated to 750°C corresponds to the existence of antiphase domains with a 3b/2 width and an antiphase shift of a/2.

Keywords

dehydroxylationSAEDdioctahedral micacation migration
Type
Research Article
Information
Clay Minerals , Volume 35 , Issue 3 , June 2000 , pp. 505 - 514
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2000

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