The Electrostatic Interlayer Forces of Layer Structure Minerals

Rossman F. Giese*
Centre de Recherche sur les Solides à Organisation, Cristalline Imparfaite, C.N.R.S. 45045 Orléans CEDEX, France
* Permanent address: Department of Geological Sciences, State University of New York, 4240 Ridge Lea Road, Amherst, New York 14226.

Abstract: Using a simple ionic model, the energy necessary to expand a layer structure by a certain distance can be calculated. This has been done for a series of 15 structures including hydroxides, 2:1 and 1:1 structures of various types. Plots of energy versus separation distance show three major groups which have common bonding properties. For large separations, the group with the strongest interlayer bonds contains the brittle micas, the hydroxides, and the 1:1 structures. Intermediate bonding structures are the normal micas and the weakest bonds occur in the zero layer charge 2:1 structures. The relative energies needed for a given separation are not constant so that for small separations the zero layer charge structures such as talc and pyrophyllite are more strongly bonded than the normal micas. These groupings correlate very well with the expandability of the structures by water and other substances. It is proposed that this approach to the study of the layer structures will provide a simple theory explaining the expansion properties of layer silicates.

Key Words: Bonding • Charge • Energy • Expansion • Interlayer

Clays and Clay Minerals; February 1978 v. 26; no. 1; p. 51-57; DOI: 10.1346/CCMN.1978.0260106
© 1978, The Clay Minerals Society
Clay Minerals Society (www.clays.org)