Size and Shape of Montmorillonite Crystallites

Edward C. Jonas and Robert M. Oliver
Department of Geology, The University of Texas Austin, Texas and Clayton Foundation Biochemical Institute The University of Texas, Austin, Texas

Abstract: Spray drying dilute suspensions of bentonitic montmorillonite produces a powder that shows totally random orientation of the crystallites within a sample large enough to diffract X-rays. The powder is collected by an electrostatic precipitator and can be handled in the normal mounting processes without introducing preferred orientation. Electron micrographs show this powder to be composed on a small scale of thin, crumpled, and rolled films. The extremely small montmorillonite crystallites that make up the film are oriented with [001] directions perpendicular to the film surface. Orientation within the plane of the film is random as shown by selected area electron diffraction. Crumpling and rolling of the film is sufficient to make the orientation of [001] directions random in three dimensions in a large sample when X-ray diffraction is registered.

The X-ray diffraction patterns all show diffraction maxima (both hk and 00l), and their relative intensities with respect to each other can be determined. The line broadening of the 06 and the 003 peaks was studied. The average crystallite size as calculated from the line broadening varied from six to eleven unit layers thick for four bentonitic montmorillonites. The average lateral dimension of crystallites varied from 140 Å to 250 Å. Ratios of lateral dimensions to thickness varied from 2.3 to 3.4.

Clays and Clay Minerals; 1967 v. 15; no. 1; p. 27-33; DOI: 10.1346/CCMN.1967.0150103
© 1967, The Clay Minerals Society
Clay Minerals Society (www.clays.org)