The Interlayer Structure of La-Vermiculite

Phillip G. Slade1, Peter G. Self2 and James P. Quirk3
1 CSIRO Land and Water, Glen Osmond, South Australia 5064
2 Ian Wark Research Institute, University of South Australia, The Levels, South Australia 5095
3 Department of Soil Science and Plant Nutrition, University of Western Australia, Nedlands, Western Australia 6009

Abstract: The structure of the interlayer cation-water system in La-vermiculite with a unit cell of a = 5.33(5), b = 9.18(6), c = 15.13(9) Å and β = 96.82(7)° has been determined in space group C2/m. Under ambient conditions, the interlayer La cations are distributed on a 3a × b superlattice which disappears on dehydration but returns on rehydration. The basal spacing does not change during the dehydration/rehydration process. The character of the superlattice spots indicate that the cation-water system, at ambient conditions, is ordered over relatively large domains. The La cations are surrounded by 8 neighboring water molecules in a distorted cubic arrangement. The spaces between the La-water clusters are occupied by triads of water molecules that are relatively mobile.

Key Words: 8-Coordinated La • La-vermiculite • Ordered • Structure

Clays and Clay Minerals; December 1998 v. 46; no. 6; p. 629-635; DOI: 10.1346/CCMN.1998.0460603
© 1998, The Clay Minerals Society
Clay Minerals Society (www.clays.org)