Infrared absorption by a mineral arises from the vibrations of its constituent atoms, and the frequencies of these vibrations are dependent on the mass of the atoms, the restraining forces of the bonds, and the geometry of the structure. The resultant spectrum of absorption frequencies is a characteristic property of the mineral which can not only serve as a fingerprint for its identification, but also give, in favourable cases, unique information on features of the structure, including the nature of isomorphic substituents, the differentiation of molecular water from constitutional hydroxyl, the degree of regularity of the structure and an indication of the family of minerals to which an unknown mineral is related.

The oxidation of benzidine to benzidine-blue on silicate minerals is shown to occur at aluminium atoms exposed at crystal edges and at transition metal atoms in the higher valency state present in the silicate lattices. The transition metals in the silicate lattice undergo chemical oxidation-reduction reactions.

Changes in the colour of the benzidine-blue radical cation with the conditions of reaction are discussed in terms of the solvent used for the reaction and its influence on the pH of the mineral surface.

The mechanism of colour reactions of clay minerals with amines, diphenylpicrylhydrazyl, tetracyanoethylene, and leuco bases are elucidated, and the results used as a guide to the reaction mechanism of polymerization reactions catalysed by clay surfaces.

The heavy metal cations studied were adsorbed by hectorite suspended in 0.05 M calcium chloride as a pH-dependent reaction in the order, Cu > Zn > (Co, Mn) > Ni. The adsorption of heavy metal cations was accompanied by the removal from solution of silicic acid released by clay dissolution. It is proposed that the reaction takes place on edge surfaces such that the clay lattice is effectively extended. This result complements other work in which it has been shown that the adsorption of silicic acid by other silicate clays results in an increased adsorption of zinc, cobalt and nickel. The present study did not provide evidence of the exchange of zinc and other cations for lattice magnesium.

The solubility of hectorite was decreased in the presence of heavy metal cations in the same order that favoured their adsorption. It is proposed that they limit the dissolution of hectorite in weakly acidic solutions by adsorption on or near the sites most prone to proton attack, that is, the magnesium ions of the octahedral layer exposed at edges and defects.

Thin green clay layers and lenses in the lower part of the Lower Oligocene Kerkom Sand near Aardebrug, east of Louvain in Belgium, were found to consist of glauconitic illite. This mineral contains about equal amounts of iron and aluminium oxides (14%) and is therefore intermediate in chemical composition between most illites and glauconites.

Comparison with the results of five published investigations of similar green clays in France and the United States shows that the green clays, which all have an intermediate glauconite-illite composition, are formed, unlike pelletoidal glauconite, in a non-marine environment. It is assumed that they developed in a lagoonal or hypersaline-lacustrine environment, probably as a result of the alteration of detrital illite-montmorillonite clay.

A study of soil formation on glauconitic parent materials in South-East England has included a mineralogical investigation of glauconite grains, heretofore identified solely by morphology. The grains have been subjected to X-ray diffraction, differential thermal and partial chemical analyses, and have been found to consist essentially of randomly interstratified micaceous and montmorillonitic clay mineral; thus all are glauconite sensu lato. Only small amounts of non-clay mineral impurities have been detected. The proportion of expandable layer material has been found to be related to the % K2O and cation exchange capacity of the specimens.

An investigation of the clay mineralogy of the molasse formations of Azerbaijan has been carried out. The results have been correlated with climate, the geochemistry of the basin of deposition, the parent rocks and the tectonic stability both in the area of erosion and the zone of accumulation. A knowledge of the relationship between these factors and the clay mineralogy of the sediments may help in the solution of paleogeographic problems.

Results from previous work on clay-mineral complexes with dimethyl sulphoxide are taken as a starting point for the development of a method to identify kaolin in the presence of chlorite. The use of this method with artificial mixtures of these minerals, and with soil clays allows the detection of kaolin when it is present in an amount higher than 5%, through the formation of a mono-layer complex with a basal spacing of 11.8 Å. Details for the use of the method are given.