Some Hydrous Micas in South African Clays and Shales

Heystek, H.

doi:10.1346/ccmn.1954.0030127

Cited by 3 publications

(1 citation statement)

References 17 publications

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“…Rowsell and De Swardt (1976) reported I/S from some borehole cores but failed to furnish compositional data. Heysteck (1954)described one example of a rectorite from the vicinity of a dolerite sill. No correlation between I/S composition and organic maturity levels has ever been attempted.…”

Section: Introductionmentioning

confidence: 99%

Smectite-to-Illite Conversion in a Geothermally and Lithologically Complex Permian Sedimentary Sequence

Bühmann

1992

Clays and clay miner.

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Abstract--The <0.5-tzm fraction of 120 samples from a lithologically complex Permian sedimentary sequence, underlying dolerite intrusive sheets, has been characterized by means of X-ray diffraction to establish I/S compositions as a function of temperature, lithology and time duration. Illitization has been active over the entire 210 m depth range and the clay data reflect both the local pattern of contact metamorphism and the more regional trend of heat flow during burial. A continuum exists in the illite proportions of the illite/smectite interstratifications with increasing distance from the intrusive sheet ranging from R = 3 with less than 5% smectite via R = 2 and R = 1 to R = 0 with up to 70% smectite. In the mixed-lithology section, individual component layers in the I/S within similar distance levels, but between contrasting lithologies, appear to vary only within a very restricted compositional range. In the massive mudstone strata, however, more silty parts contain I/S of a higher degree of ordering and lower expandability. Calcite contents are reflected in a higher rate of chlorite formation, but not in the I/S composition. A satisfactory inverse correlation was found between percent smectite in I/S and vitrinite reflectance in the lithologically complex section. R = 1 interstratifications are associated with a maximum vitrinite reflectance of 1.07-1.29 and R > 1 phases with 1.93-2.7, indicating that time duration is not a controlling factor in the illitization process in this facies. R = 0 interstratifications are present in a massive mudstone/siltstone sequence situated furthest from the igneous intrusives, and display vitrinite reflectance values of 1.42-1.52. No satisfactory explanations for this finding can be offered.

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Section: Introductionmentioning

confidence: 99%

Smectite-to-Illite Conversion in a Geothermally and Lithologically Complex Permian Sedimentary Sequence

Bühmann

1992

Clays and clay miner.

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Wetting-induced layer contraction in illite and mica-family relatives

Kühnel

Gaast

Broekmans

et al. 2017

Applied Clay Science

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Quantitative determination of the interlamellar volume in an interstratified mica-smectite soil clay

Jones

Greenland

1980

Clay miner.

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Two well-characterized soils containing substantial amounts of interstratified mica-smectite have been examined by a combination of techniques in an attempt to correlate the characteristics of the interlamellar surfaces with other properties. The techniques used included XRD and chemical analyses, determination of surface area by nitrogen sorption and by desorption of water and ethylene glycol monoethyl ether vapour, and determination of cation exchange capacity. Reasonable agreement was found between the results obtained for the proportion of expanding or smectite-like surfaces, although estimates by XRD, especially when coarser material ( > 2/~m) was included, were generally lower than those obtained by the other methods. The mean density of charge on the surfaces of the soil clays appeared to be similar to that of smectite. The decrease in porosity observed for both soils dried by the critical point method was largely accounted for by the decrease in volume associated with the loss of interlamellar water from the smectite-like interlamellar surfaces included within the clay fraction.Many soil clays which show substantial swelling and shrinkage in response to changes in moisture content contain smectites in the clay fraction. Commonly the smectite is interstratified or mixed with other 2:1 lattice clays. It is sometimes suggested that the swelling behaviour of the soil is due to adsorption of water in the interlamellar regions of the clay crystals. This may be true in some sodic soils, but where Ca 2+ is the dominant exchangeable cation Aylmore & Quirk (1962) and others have established that the interlamellar regions make little or no contribution to the swelling of soils observed in field conditions. However, if the absorption and loss of water is to be related to the swelling behaviour of soil clays over a wider range of water contents it is essential that the contribution of the interlamellar surfaces be known quantitatively.Mooney et al. (1952) showed that at relative water vapour pressures <0.05, Camontmorillonite adsorbed one layer of water molecules only in the interlamellar region (d001 ,-~ 12.5 A); at higher vapour pressures two layers of water molecules were adsorbed (d001 ,-~ 15 A), and above P/Po~0.90, three layers of water molecules were present (d001 ~ 19 ~). However, little information is available to relate this work to the swelling behaviour of soil-clays, where the interlamellar charge density may differ considerably from that of the montmorillonite studied by Mooney et al. (1952).The present paper reports work conducted to determine quantitatively the interlamellar water sorption of two soil clays, whose overall swelling behaviour has already been studied in some detail (Lawrence et al. 1979).

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Some Hydrous Micas in South African Clays and Shales

Cited by 3 publications

References 17 publications

Smectite-to-Illite Conversion in a Geothermally and Lithologically Complex Permian Sedimentary Sequence

Smectite-to-Illite Conversion in a Geothermally and Lithologically Complex Permian Sedimentary Sequence

Wetting-induced layer contraction in illite and mica-family relatives

Quantitative determination of the interlamellar volume in an interstratified mica-smectite soil clay

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