Electron-Optical Investigations on Montmorillonites—II: Morphological Variations in the Intermediate Members of the Montmorillonite-Beidellite Series

N. Güven and R. W. Pease
Department of Geosciences, Texas Tech University, P.O. Box 4109, Lubbock, Texas 79409, U.S.A.

Abstract: Dioctahedral aluminum smectites from bentonite deposits in Argentina, Brazil, Czechoslovakia and Japan represent, according to the MgO content of the bulk samples, intermediate members in the montmorillonite-beidellite series. The smectite particles in these samples occur in a variety of forms such as; (a) laths and diamond-shaped units with a well developed crystal habit, (b) loosely folded aggregates with an irregular morphology and (c) flat and compact lamellae with well developed {001} forms but with complete lack of {hk0} forms. Such lamellae have been described in two groups: the thin ones (10–50 Å) and the thicker ones. Thin lamellae may give SAD spot patterns with a non- hexagonal symmetry. Lamellae having thicknesses greater than 50 Å resemble a single crystal but their SAD patterns indicate that they do not have a three-dimensional periodicity.

The question arises whether the morphologically different particles in a sample belong to the same intermediate phase or if they represent different members in the montmorillonite-beidellite series coexisting in the same sample.

Clays and Clay Minerals; July 1975 v. 23; no. 3; p. 187-191; DOI: 10.1346/CCMN.1975.0230304
© 1975, The Clay Minerals Society
Clay Minerals Society (www.clays.org)