Measurement of Fundamental Illite Particle Thicknesses by X-ray Diffraction Using PVP-10 Intercalation

D. D. Eberl1, R. Nüesch2, V. Sucha3 and S. Tsipursky4
1 U.S. Geological Survey, 3215 Marine Street, Boulder, Colorado 80303
2 ETH, IGT-ClayLab, Institut für Geotechnik, Sonneggstrasse 5, CH-8092 Zürich, Switzerland
3 Dept. of Geology of Mineral Deposits, Comenius University, Mlynská Dolina G, 842 15 Bratislava, Slovakia
4 Nanocor, 1350 W. Shure Drive, Arlington Heights, Chicago, Illinois

Abstract: The thicknesses of fundamental illite particles that compose mixed-layer illite-smectite (I-S) crystals can be measured by X-ray diffraction (XRD) peak broadening techniques (Bertaut-Warren-Averbach [BWA] method and integral peak-width method) if the effects of swelling and XRD background noise are eliminated from XRD patterns of the clays. Swelling is eliminated by intercalating Na-saturated I-S with polyvinylpyrrolidone having a molecular weight of 10,000 (PVP-10). Background is minimized by using polished metallic silicon wafers cut perpendicular to (100) as a substrate for XRD specimens, and by using a single-crystal monochromator. XRD measurements of PVP-intercalated diagenetic, hydrothermal and low-grade metamorphic I-S indicate that there are at least 2 types of crystallite thickness distribution shapes for illite fundamental particles, lognormal and asymptotic; that measurements of mean fundamental illite particle thicknesses made by various techniques (Bertant-Warren-Averbach, integral peak width, fixed cation content, and transmission electron microscopy [TEM]) give comparable results; and that strain (small differences in layer thicknesses) generally has a Gaussian distribution in the log-normal-type illites, but is often absent in the asymptotic-type illites.

Key Words: Bertaut • Fundamental Illite Particles • Illite • Illite-Smectite • Mixed-Layering • Peak Broadening • Polyvinylpyrrolidone • Warren-Averbach • X-ray Diffraction

Clays and Clay Minerals; February 1998 v. 46; no. 1; p. 89-97; DOI: 10.1346/CCMN.1998.0460110
© 1998, The Clay Minerals Society
Clay Minerals Society (www.clays.org)