Changes caused by pressures between 0 and 20 K bar on two samples of kaolinite have been studied. Increased pressure causes the samples to lose crystallinity, shown by a decrease in the Hinckley, Lietard and reference intensity ratio indices, as well as by the crystallite size measured from the 001 reflection. Results from DTA and solid state NMR show slight or no differences between the compressed and natural samples. Nonetheless, thermogravimetry reveals that the pressure treatment lowers the temperature at which dehydroxylation begins, but, unlike the grinding process, pressure does not alter the OH content of the samples. As a result of the increase in pressure, the IR spectra of the samples show a gradual increase in the intensity of the band at 1104 cm -1 with respect to 1112 cm -1. An increase in intensity can also be observed in the band at 936 cm ~ with respect to the band at 912 cm -1. Examination by electron microscopy reveals the existence of a large number of defects such as fractures, bends and deformations of the sheets, etc.; these are responsible for the decrease in crystallinity.

The desorption of methanol (MeOH), propan-1-ol (n-PrOH), propan-2-ol (i-PrOH) and 2-methylpropan-2-ol (t-BuOH) from Na+-, Ca2+-, Al3+-, Cr3+- and Fe3+-exchanged montmorillonite has been studied using variable temperature infrared (IR) spectroscopy and thermogravimetric analysis (TGA). Alcohol-saturated trivalent cation (M3+) exchanged samples exhibit maxima in the derivative thermograms at 20 and 110°C (MeOH), 30 and 160°C (n-PrOH), 20 and 110°C (i-PrOH) and 20, 55 and 80°C (t-BuOH). Alcohol-saturated Na+ and Ca2+-exchanged montmorillonite samples exhibit maxima at higher temperatures in the i-PrOH (20 and 140°C) and t-BuOH (30, 90 and 110°C) desorption profiles but at the same temperatures for MeOH and n-PrOH. Mass spectroscopic analysis of the vapours desorbed from the alcohol-treated samples show that the low-temperature maxima in the alcohol desorption from the M3+-exchanged clays are due to unchanged alcohol, whilst those occurring at 80°C (t-BuOH), 110°C (i-PrOH) and 160°C (n-PrOH) are due, in the main, to alkene produced from the intramolecular dehydration of the respective alcohol. Changes in the IR spectra of the adsorbed alcohols occur at temperatures which are in accord with the mass spectral data. No mass spectral evidence was found for the formation of dialkylethers via the competing intermolecular process but dimerisation and oligomerisation of t-BuOH were observed.

Glauconite and Fe-smectite, which can be distinguished by their peculiar morphology and stacking sequences, coexist in the Galapagos Spreading Centre hydrothermal mounds. Analytical electron microscopy (AEM) data suggest that Fe is entirely in octahedral sites in Fe-smectite whereas glauconite is K-rich with Fe in tetrahedral and octahedral sites. However, the Mossbauer spectra, recorded at various temperatures for samples containing both smectite and glauconite, were satisfactorily analysed with three overlapping doublets corresponding to Fe in octahedral sites. The contradictory results obtained with the two methods are explained by the presence of small particles of iron oxide intimately associated with glauconite. These particles were detected in Mossbauer spectra obtained at 77 K and 4·2 K and were observed by transmission electron microscopy. Iron oxide is a secondary phase formed by alteration of smectite. These data are in good agreement with the hypothesis that the smectite-glauconite reaction, which occurs at 30 m and low temperature in the Galapagos hydrothermal mounds, is a dissolution-precipitation process, dissolution of Fe-rich smectite being followed by precipitation of glauconite and iron oxides.

Methylene blue (MB) and crystal violet (CV) have been found to be adsorbed in amounts greater than the cation exchange capacity (CEC) of clays (Hang & Brindley, 1970; Ghosal & Mukherjee, 1972; Venugopal & Nair, 1974).

In previous work (Rytwo et al., 1991), it was shown that CV adsorbs to montmorillonite up to 1·4 mmole dye/g clay. The amount of dye added in those experiments was up to 1·6 mM/g clay. Yet, when the added amount of CV and MB was 3·5 mM/g (Rytwo et al., unpublished), almost 1·6 (200% of the CEC) and 1·2 mM/g clay, respectively, were adsorbed. Margulies et al. (1988), who studied the adsorption of thioflavin T and MB to montmorillonite, showed that these dyes adsorb up to 1·4 and 1·2 mM dye/g clay, which corresponds to 175% and 150% of the CEC, respectively.

When studying surface free energies of clays in relation to clay composition, we calculated that in some instances the aggregate stability should be higher for Na- then for Ca-forms. This raised the question as to whether the results obtained with the surface free energy approach are reliable for estimation of soil aggregate stability. The aim of the present work was to measure the surface free energy components and attractive forces for a clay calculated from measurements of the contact angle of glycerol, diiodomethane and cis-decalin and to compare them with results of penetrometrical measurements.

Oxygen isotope analysis of clay minerals presents several practical difficulties. These include their very fine grain size, the presence of both hydroxyl and non-hydroxyl oxygen, adsorbed water and, where clays from oil reservoirs are concerned, the possibility of hydrocarbon contamination. To develop routines which would minimize these problems while leaving the isotope systematics of the clay undisturbed, a series of oxygen isotope analyses were made under different running conditions of the API Standard Illite–the Fithian illite.

Palygorskite has been widely reported as a clay phase in the Recent sediments of the northern Arabian Gulf (e.g. Aqrawi & Sadooni, 1988). It is usually thought to have originated from the sediments and soils of the Mesopotamian flood plains introduced by northwesterly (Shamal) winds (e.g. A1-Bakri et al., 1984). A1-Rawi et al. (1969) and Eswaran & Barzanji (1974) have detected palygorskite within Mesopotamian soils. This paper describes the occurrence of palygorskite in the Recent sediments of southern Mesopotamia and its possible origins will be discussed.