By means of a gold decoration transmission electron microscopy (TEM) technique, interlaced spiral steps with a 10 A step height were observed on (001) surfaces of lath-shaped or elongated hexagonal rectorite crystals, i.e. interstratihed mica-smectite minerals, from the Goto pyrophyllite deposit in Nagasaki Prefecture, Japan. This is the first direct evidence to demonstrate that the growth of interstratified mica-smectite takes place by the spiral growth mechanism. The interlacing pattern is interpreted as appearing by co-operation of two hexagonal spiral layers of mica and smectite-like layers which have originated from a single dislocation and are stacked by rotation of 60°.

Six different X-ray diffraction (XRD) methods for determining the relative amounts of 2M1 and 1M white K-mica polytypes were compared. Unoriented samples of different concentrations of the two polytypes were prepared using the technique described by Handschin & Stern (19X9) and Stern (1991). An evaluation of different XRD techniques reported in the literature revealed that the method proposed by Caillére et al. (1982) is the most accurate. The main reasons are the use of the 1M 112 and 2M1 025 reflections with relatively strong intensities, showing no superposition with feldspar reflections, and being only slightly affected by sample preparation effects.

The nature and characteristics of 1:1 phyllosilicates (crystallinity, order and proportion of kaolinite, disordered kaolinite and 7 Å-halloysite) in deep palaeoweathering profiles developed on granitic rocks in Central Spain have been studied. The profile displays a lower part of non-silicified saprolite and an upper part of silicified saprolite, with or without a sedimentary silicified cover. The <2 µm fraction was studied using XRD, TG-DTA and IR techniques. Towards the top of the profile there is a progressive decrease in both 1:1 phyllosilicates and kaolinite contents and an increase in opal. In the upper part (silicified saprolite) two weathering fades can be distinguished: the 'white fades', in which the crystallinity of kaolinite is greater than in the 'red facies. The kaolinite in the upper parts of the profile is probably a remnant of that existing in the non-silicified saprolite, whereas disordered kaolinite and 7Å-halloysite are, at least in part, a product of transformation and/or neoformation under more surface-like conditions.

Vermicular glaucony grains exhibit external features which include longitudinal grooves, ridges and striations, and transverse partings, the last defining packets of green minerals oriented at right angles to the longitudinal features. The grooves and striations are reflected in internal structures, as are transverse partings in the form of transverse voids and micaceous cleavage. There are some gross similarities in the morphological features of vermicular glaucony with those described for decapod faecal pellets. However, reanalysis of the original evidence used to support formation of some vermicular glaucony from decapod faecal pellets highlights discrepancies and alternative explanations. This suggests that vermicular glaucony grains do not form by glauconization of decapod faecal pellets.

Different types of heterogeneity were shown in F/OH/A1 pillared fluorohectorite by combined use of X-ray and selected area electron diffraction, high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray (EDX) methods: interlayer distances heterogeneity (layer stacking order imperfections); domain structure heterogeneity; and phase heterogeneity (formation of secondary phases from pillaring solutions). The role of ageing of pillaring solutions and pillared smectites was revealed and discussed.

Addition of methanol, ethanol, and n-propanol to aqueous dispersions of Namontmorillonite (2% w/w) reduces the apparent viscosity and the yield value. In the presence of NaCl the flow parameters increase to a maximum at medium alcohol concentration. Thus, the gel strength of Nabentonite dispersions can greatly change with the alcohol content of the dispersion. This is probably caused by the transition of dispersed clay mineral particles (individual silicate layers or lamellae of a few of these layers) to band-type networks with optical homogeneity and weakly attractive particle-particle interaction. When attraction between the particles becomes too strong at high alcohol concentrations, the bands are condensed to short fragments and, eventually, freely moving particles, reducing the viscosity and the yield value.

The interparticle interaction energy is calculated for the constant charge model by van Olphen's (1977) method. Agreement with the experimental results is only obtained when the Stern layer adsorption is governed by a specific adsorption energy μ, which increases with decreasing dielectric constant.

The flow behaviour of Wyoming bentonite dispersions was studied in water and water-alcohol mixtures (methanol, ethanol, n-propanol) with or without the addition of NaCl. The yield value τo and relative apparent viscosity τ*rel (= τ* (dispersion/τ* (medium) at γ = 94.5 s-1) increase to a maximum and then decrease with increasing alcohol content. The increase of the flow values is caused by face-to-face aggregation. Formation of band-type networks is a consequence of the enhanced attraction between the silicate layers in water-alcohol mixtures. At higher alcohol contents the bands are contracted to discrete particles. Both effects are considerably strengthened by calcium ions which are present in the crude bentonite.

The adsorption of the insecticide methomyl (S-methyl N-(methylcarbamoyloxy)thioacetimidate) by smectites with different layer charge (SWy and SAz montmorillonites and SH-Ca hectorite) has been determined. Adsorption has been expressed as the adsorbent/adsorbate distribution coefficient Kd, which increased when the layer charge of the smectite decreased. The Kd values for homoionic SWy montmorillonite samples increased when the ionic potential of the interlayer cation decreased, except for SWy-Fe3+. Infrared (IR) spectra and X-ray diffraction (XRD) analysis of the SWy-K+ and SWy-Na+ montmorillonites treated with methomyl suggest that pesticide molecules interact through polar bonds with the interlamellar cation. In the case of SWy-Fe3+, kinetic studies, high performance liquid chromatography (HPLC), IR and XRD data indicated that adsorption and degradation both account for the high Kd value obtained.

The affect of competing surfactant molecules, n-decyltrimethylammonium bromide (C10TAB) and n-hexadecyltrimethylammonium bromide (C16TAB), on the adsorption equilibrium between methylene blue (MB) and Na+-montmorillonite has been studied using visible spectrophotometry. The MB competed effectively with both these surfactants and also tetramethylamntonium ions, which were used as a model for the surfactant head group. At loadings up to 50% of the CEC of the clay, all of the MB was associated with the clay or clay/surfactant system. Evidence for the presence of monomer, MB+, dimer, (MB+)2, trimer, (MB+)3, and protonated monomer, MBH2+, was obtained in each case, with the trimeric form dominating at loadings >5% of the CEC. The spectra of adsorbed MB reflected the difference in chain length between C10TAB and C16TAB and indicated that a significant amount of monomeric, MB+, was solubilized in the C16TAB surfactant clusters on the clay surface. Pre-adsorbed MB was not displaced by added C16TAB surfactant.

Six Spanish kaolins were studied to determine the potential application of their crystallinity for pharmaceutical purposes. Particular attention was paid to the effect of crystallinity on sodium amylobarbitone release in water, when the drug was prepared as granulates with kaolin. Crystallinity was estimated empirically in various granulometric kaolin fractions by examining X-ray diffraction (XRD) patterns, infrared spectra and morphology as shown by scanning electron microscopy (SEM). Crystallinity was usually moderate with a mean Hinckley index of (1.69. Statistically significant relationships were found between the XRD indices and other kaolin characteristics such as total iron content and mean particle size. The different degrees of crystallinity also appear to be related to the fabric type and morphology of individual aggregates and particles (SEM). The release of sodium amylobarbitone increases with kaolin crystallinity, as estimated by the indices HB1 (Hughes & Brown, 1979) and RWI (Range & Weiss, 1969), according to the formula y = 43.668 + 3.631 HBI -84.711 RWI. Our findings suggest the possibility of preparing sustained-release formulations with controlled drug release by using kaolins of different degrees of crystallinity as excipients.

The most widely used procedure for determining the cation exhange capacity (CEC) of a clay involves ammonium ion exchange, followed by Kjeldahl measurement of the ammonia released on treatment with alkali (Grimshaw, 1971; Mackenzie, 1951). The method is experimentally quite difficult, prone to error and time consuming.