Analysis of illite-smectite interstratification

Abstract

A new approach to understanding illite-smectite interstratification is formulated which incorporates the concepts of interparticle diffraction and elementary illite particles. The analysis shows that nearest-neighbour ordering, non~ ordering, ordering at the illite end of the composition scale, and the lack of ordering at the smectite end can be explained by expandable interfaces between elementary, i.e. two silicate layers, and larger illite particles. Ordering in I/S clays is significant only when the probability of occurrence of illite is ~ 80~. New concepts proposed are an order parameter (~0) and an expansion parameter (fl). Interparticle diffraction implies that I/S clays are unusual among all crystalline materials since their XRD size is equal to or larger than the size of their constituent physically separable particles.

Decomposition of X-Ray Diffraction Patterns: A Convenient Way to Describe Complex I/S Diagenetic Evolution

“…The termination of elementary diffracting units on smectitic edges, suggested by Veblen et al (1990) and Giiven (1991), also deserves a test to check its influence on XRD profiles. Additionally, models that incorporate the concepts of interparticle diffraction and elementary illite particles (Corbato and Tettenhorst, 1987;Tettenhorst et al, 1990) may be an eventual alternative to the MacEwan crystallite model used in this paper, and others, to simulate X-ray diffraction by mixed-layered clay minerals.…”

The I-S contact in 10 Å-17 Å interstratified clay minerals

“…The value of/3, i.e., the level of order, made no discernible difference in the calculated profiles for any Pi > 0 and < 0.5 as inferred in the analysis (Corbat6 & Tettenhorst, 1987). The profile forpi = 0.5 is shown in Fig.…”

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ABSTRACT: Calculated X-ray diffraction profiles of 10 A-17 A interstratified clay minerals, which make allowance for fundamental illite particles, confirm many of the inferences made in a previous analysis by Corbat6 & Tettenhorst (1987). However, some of these profiles do not appear to match well with patterns obtained from real interstratified clay minerals.

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“…A goal of this study is to try to gain additional insight into these silicate layers by testing the effect of the premises on calculated XRD profiles. The initial model of Corbat6 & Tettenhorst (1987) was based on four premises, the first two being operational definitions of illite and smectite.…”

“…Variations in the XRD patterns in sequences of samples have allowed investigators to assess the effect of temperature, time, burial depth, proximity to igneous bodies, ion mobility, and ion competition in the transformation of smectite to illite. Corbat6 & Tettenhorst (1987) formulated a different approach to the analysis of I-S clay minerals. The objective of that study was to try to provide additional insight by incorporating the concepts of fundamental illite particles and expandable interfaces (interlayers) between illite particles (McHardy et al, 1982; Nadeau et al, 1984a,b).…”