Chemistry of Illite/Smectite and End-Member Illite

Jan Środoń1, David J. Morgan, Eric V. Eslinger, Dennis D. Eberl and Michael R. Karlinger
Institute of Geological Sciences, Polish Academy of Sciences 31-002 Krakow, Senacka 3, Poland
British Geological Survey, 64 Gray's Inn Road, London WC1X 8NG, United Kingdom
Cities Service Oil and Gas Corporation, P.O. Box 3908 Tulsa, Oklahoma 74102
U.S. Geological Survey, MS 404, Federal Center Denver, Colorado 80225
1 Visiting exchange scientist at the Water Resources Division, U.S. Geological Survey, Denver, Colorado.

Abstract: Chemical data from three different series of diagenetic illite/smectites (I/S), analyzed statistically by two regresion techniques, indicate that the content of fixed-K per illite layer is not constant, but ranges from ∼0.55 per O10(OH)2 for illite layers in randomly interstratified I/S (R=0; > 50% smectite layers) to ∼1.0 per O10(OH)2 for illite layers formed in ordered I/S (R>0; <50% smectite layers). By extrapolation of the experimental data, the following chemical characteristics were obtained for end-member illite derived from the alteration of smectite in bentonite: average fixed-K per illite layer = 0.75 per O10(OH)2; total charge = about −0.8; cation-exchange capacity = 15 meq/100 g; surface area (EGME) = 150 m2/g.

Key Words: Bentonite • Chemical composition • Diagenesis • Illite • Illite/smectite • Smectite

Clays and Clay Minerals; August 1986 v. 34; no. 4; p. 368-378; DOI: 10.1346/CCMN.1986.0340403
© 1986, The Clay Minerals Society
Clay Minerals Society (www.clays.org)