The aim of this paper is to show how van der Waals forces may account for profound changes in the IR spectra of alkylammonium saturated montmorillonite and the effect of adsorbed water molecules. IR spectra recorded on alkylammonium montmorillonite films submitted to vacuum and after exposure to water vapour show, in addition to the shifts in the stretching and deformation bands expected when hydrogen bonding is present, marked changes in the intensity of the CH2 and CH3 deformation bands. All these observations are explained by the following model: (1) in the absence of water, the aliphatic chains are tightly held between the oxygen atoms of the silicate layers with their axis parallel to the 001 planes; and (2) hydration causes a rotation of the organic chain of the dialkyl derivatives while it does not affect the orientation of the monoalkylammonium cations. Moreover in the former situation, the symmetric deformation band of CH3 is removed because of the increase of the reduced mass due to the immobilization of the chain between the oxygen atoms.

A method is described for plotting and comparing measurements made on kaolinite clays. In this the ratio of the two strongest bands in the OH-stretch region of the spectrum (band maxima at 3695–3700 cm−1 and 3620–3625 cm−1) of an oriented preparation at 45° incidence is plotted against the corresponding ratio from the spectrum of a randomly oriented preparation. Both ratios are affected by the shape of the kaolinite particles and methods for minimizing this are given. The position of a kaolinite upon a plot so prepared gives information on the following points: (a) the type of kaolinite, (b) the degree of crystallinity of the kaolinite, (c) the shape of the kaolinite particles.

The infrared spectrum of water adsorbed on K-hectorite has been studied in the frequency range 2600–4000 cm−1 on samples equilibrated with relative humidities of 0% to 100%. The model proposed by J. Mamy for the molecular array of water upon the mineral surface has been used as a starting assumption. A ‘unit cell’ made of two H2O molecules is then considered as a possible theoretical basis for the interpretation of the infrared spectrum. When taking into account this unit cell six stretching frequencies may be anticipated. The six components of the OH stretching band are clearly resolved at −95°C at room temperature a Curve Resolver was used to analyse the composite band, which was recorded at various incident angles (0–45°). From the variation of the integrated absorption of each component band given by the curve resolver, the orientation of the dipolar moment is calculated, and compared with the theoretical one deduced from the model.

Mossbauer spectroscopy was used to study the valence and bonding changes of iron in (a) lattice sites, and (b) cation exchange sites during thermal treatment of kaolinite and halloysite. Lattice iron which is initially in octahedral sites occurs in octahedral and tetrahedral sites at the completion of the thermal reactions. At temperatures below 650°C some divalent ions in cation exchange positions become trivalent and assume octahedral co-ordination, which they retain until the later stages of mullite formation. The implications of the work on the high temperature reaction mechanism and structural sequence are discussed.

The mineral phases and the distribution of major, minor and trace elements in the clays and bed rocks of two bore-holes at Adda and Chaubatta of the Birbhum area have revealed an intimate relationship of the kaolin-rich clays with the bed-rock of Adda. The possibility of a common origin for the clay deposits at Chaubatta, lying close to the Rajmahal trap formations, and at Adda, lying close to the Archaean boundary, has been inferred from trace element distribution and other factors. A genetic relationship of the clay deposit at Adda with the bed-rock, altered Archaean gneiss, has been established, but there is no significant relationship of the Chaubatta clay deposit with its bed-rock, the weathered basalt.

The lateritic cappings above the kaolin-rich clays of Adda and Chaubatta areas are explained as being formed from kaolinite in the weathering sequence as the end-product of intensive desilication under conditions of intensive leaching and increasing acidity near the surface.

Although Thermal Analysis is a useful technique in characterizing the clay constituent of a potentially valuable clay deposit, it is, perhaps, even more useful when the type and amount of non-clay impurities are important factors in its commercial appraisal. The effect of impurities on the physical and chemical properties of the clay may determine its potential uses in bulk, or it may be advisable to remove the impurity, either to improve the grade and quality of the clay or to provide a useful by-product. The application of both qualitative and quantitative thermal data, in the analysis and control of laboratory work in this field, is demonstrated by its use in the assessment of materials such as evaporite-rich clays, siliceous clays, and high-alumina clays.

Studies were conducted on the feasibility of using the Dupont 900 thermal analyser for quantitative estimation of clay minerals. The results indicate that kaolinite, gibbsite, goethite and calcite can be determined quite accurately and in small concentrations provided there are no serious interferences. Quartz in excess of 5 mg or more can be determined with a reasonable degree of accuracy. Approximate estimates of montmorillonitic contents of soil clays can be made by measuring the areas of the low temperature endotherms of samples which were equilibrated over saturated Mg(NO3)2.

Two types of cells for magnetic separation of clay minerals in aqueous suspension, were designed. The ceils can be used with a standard Franz Isodynamic Separator. The technique reported is effective in separating chlorite from a natural clay mixture.

Adsorption isotherms for an homologous series of primary aliphatic alcohols from aqueous solution by montmorillonite and kaolinite saturated with either sodium or calcium ions have been determined. The results show that adsorption is a function of chain length and exchangeable cation in the case of the more insoluble alcohols. Exchangeable cation does not affect the adsorption of the soluble alcohols to any significant extent. Adsorption of the longer chain alcohols occurs in voids in the mineral aggregates.