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Mixed magnesium-aluminium hydroxides. II. Structure and structural chemistry of synthetic hydroxycarbonates and related minerals and compounds

Published online by Cambridge University Press:  09 July 2018

G. Brown
Affiliation:
Rothamsted Experimental Station, Harpenden, Herts., EnglandandMusée Royal de l'Afrique Centrale, Tervuren*
M. C. Gastuche
Affiliation:
Faculté des Sciences Agronomiques et Institut lnterfacultaire des Sciences Appliqués, Université de Louvain, Belgium

Abstract

A structural scheme is proposed for the synthetic Mg-Al hydroxycarbonates described in Part I (Gastuche, Brown & Mortland, 1967) based on chemical and X-ray powder data. The structure consists of positively-charged brucite-like layers in which Al replaces Mg up to a maximum of about one in three sites. The positive charge is balanced by an interlayer sheet containing carbonate groups and water molecules. The idealized structural formula for the Al-rich material is:

[Mg4Al2(OH)12]2+ [CO3.3H2O]2−.

A similar structural scheme seems to apply to many other materials including the minerals of the pyroaurite group, the compound 4CaO.Al2O3.13H2O and the related mineral hydrocalumite, a nickeliferous magnesium hydroxide mineral described recently and to many synthetic products that have been referred to as double sheet structures.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1967

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