Compositional Variation in Component Layers in Natural Illite/Smectite

Abstract

Abstract--Published chemical data for suites of mixed-layer minerals from diagenetic sedimentary rocks, hydrothermally altered tufts, and a metasomatic bentonite bed indicate that the layer charge and composition of the different components of illite/smectite (I/S) differ from one geological environment to another. It appears that the composition of the elemental smectite and illite layers in the I/S is more or less constant for samples within each geologic setting. In the examples considered, the smectite layers are predominantly montmorillonitic in character (i.e., the charge is in the octahedral site), whereas the illite layers show different types of charge sites, depending upon the suite studied. Illite layers appear to have about the same charge in all three suites studied, slightly more than 0.7 per O~o(OH)2 unit, whereas the smectite layers in the different suites range in charge from about 0.3 to 0.7 per Oao(OH)2 unit. Cationexchange capacities reflect these differences in charge, although not ideally. The differences in the composition of the component layers in each geologic suite of mixed-layer clays are probably due either to differences in the bulk chemistry of the rocks in the different suites or to differences in intensive variables, such as temperature and pressure, of the regime under which they have formed.

Chemistry of illite-smectite inferred from TEM measurements of fundamental particles

“…The present study was undertaken in an attempt to verify these diverse findings, as well as equally diverse opinions on the charge density of smectite layers (Nadeau & Bain, 1986;Srodori et al, 1986;Velde & Brusewitz, 1986). High-resolution transmission electron microscopy (HRTEM) was used to check the accuracy of TEM data.…”

“…8 for all the sample sets discussed plus the Montana Cretaceous bentonites of Eslinger et al (1979) and the Kinnekulle Ordovician bentonites of Brusewitz (1986). The exchangeable cation analyses of the last two sets were questioned, but any possible error cannot affect the silicate layer composition appreciably.…”

“…For the same reason, the Eslinger et al (1979) data were not interpreted. The data of Hower & Mowatt (1966) and Brusewitz (1986) were not utilized because they are contradictory: for samples from the same Kinnekulle B bed the values of Brusewitz are twice as large as those of Hower & Mowatt. For Shinzan sericites, the exchangeable cation content was calculated from CEC by means of eqn.…”

Diagenetic Structural Transformations in North Sea Jurassic Illite/Smectite

“…Hansen and Lindgreen (1989) concluded that this sampie is a bentonite originating from volcanic ash, whereas the other samples originate from detrital, R0-ordered I/S with P~ ~0.65. According to Velde and Brusewitz (1986), I/S originating from volcanic ash has a larger tetrahedral charge than I/S in shales. Thus, the chemical results of the present investigation suggest that the I/S in sample 2/7-3,3365m formed from volcanic ash.…”

Comparison of Clay and Zeolite Mineral Occurrences in Neogene Age Sediments From Several Deep Wells

“…The R = 1 ordered structure was encountered for samples having 40 to 50% smectite layers. Estimation of percent smectite was made using the method of Velde et al (1986) for air-dried samples. These identification methods were used because of the low intensity of the smectite peaks at ~9A (indicating that a small number of layers is present in the crystallites) and because of the frequent interference of zeolite, mica, and quartz peaks with I/S reflections.…”