A scheme is presented for the semi-micro analysis for the major elements in clay minerals, based mainly on improvements to conventional colorimetric methods. Silica and alumina are determined after fusing a 50-mg sample with sodium hydroxide. Titanium, total iron, calcium, magnesium, phosphorus and manganese are determined colorimetrically on a hydrofluoric-sulphuric acid digest of a 50-mg sample; sodium and potassium are determined flame photometrically on the same digest. Ferrous iron is determined separately. Additional methods for the determination of total water, total sulphur and fluorine are indicated.

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.

Interlayer K in eleven trioctahedral micas, with compositions ranging from fluorphlogopite to biotite, was replaced by treating cut flakes with aqueous solutions of Na salts at controlled pH values. Replacement in natural micas was faster at pH 4·5 than at pH 9, and there is a co-operative action or synergy of H+ and Na+ in replacing K+. The synergetic effect of H+ tends to be greatest in micas that lose most net negative charge when K is replaced, and increases when Fe2+ in biotite is oxidized by heating. Possible relationships between the synergetic effect and the chemical composition of micas are discussed in relation to the structure and chemical changes in the aluminosilicate layers when K is exchanged, and it is concluded that incorporation of protons into the structure is responsible for the synergetic effect.

A naturally occurring macroscopic sodium vermiculite from Unst, Shetland is described. It is similar in many respects to synthetic materials recently prepared from phlogopite by potassium replacement. In other respects, however, it is more akin to macroscopic Mg-vermiculites.

Poorly crystalline inorganic materials were removed from soil clays of different origin and mineral composition by successive treatments with sodium dithionite, 2 % Na2CO3 and 0·5 N NaOH. Techniques are described whereby difference spectra representing the infrared absorption of the materials removed by the treatments can be obtained. These spectra indicate that the materials dissolved are related to the mineral composition of the soil clay. Dissolution of allophanes of different composition was only proved for two volcanic ash soil clays in which these dominated. Layer silicates, probably including kaolin, were dissolved from the clay fractions of the red-brown earth and krasnozem studied. In addition, alumina-rich gel-like material and gibbsite, but no allophanes, were dissolved from another volcanic ash soil clay in which gibbsite and layer silicates are present in considerable amounts.

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.

Methods are described for estimating a valuable absorption coefficient for OH stretching bands of micas: the integrated parallel absorption coefficient K.

From a correlation between this coefficient and the OH content of biotites and phlogopites, it was found that the parallel absorption coefficient per hydroxyl group in these trioctahedral micas is not appreciably influenced by the chemical composition and the direction of the OH bond. A clear deviation was observed for the low frequency band of a biotite characterized by a well-ordered orientation distribution for the corresponding hydroxyl groups.

The integrated parallel absorption coefficient of muscovite is proportionally 2·5 to 3 times larger than that of trioctahedral micas.

The influence of sorbed cations and hydration on the a and b dimensions of montmorillonite, has been established by the selected area diffraction technique (S.A.D.) and by X-ray diffraction analysis. Concepts on the bonds and interaction mechanism of aluminosilicate layers with sorbed cations and water molecules (which form hydrate-ionic layers) are discussed. These concepts also indicate the basic stages of the sorption process and the formation of the montmorillonite structure. Assuming that aluminosilicate and hydrate-ionic layers represent a single crystal-chemical structure, the change of configuration of the aluminosilicate layers and dimensions of the montmorillonite lattice are explained.

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.

Water released by dehydroxylation was trapped in clay compacts during reactive hot pressing. The dynamic conditions of water pressure and temperature produced in the compacts modified the high temperature reactions of kaolinite. Kaolinite was converted to pyrophyllite or mullite in the temperature range 600-700°C depending on the applied pressure. Oriented aggregates of clay were used to determine orientational relationships between kaolinite and the high temperature phases. Structural continuity was observed in the reactions through the basal planes of kaolinite and pyrophyllite to the (130) plane of mullite.

The effects of simultaneous additions of electrolyte and peptiser to dispersions of the synthetic hectorite-like clay, Laponite, have been studied. It has been unexpectedly discovered that whereas many cations cause gelling and flocculation of the dispersions as expected by colloid chemical theory, some cations actually stabilize the sols obtained with peptiser. A relationship has been found between the effectiveness of the cations in increasing sol stability and their size and charge.

The effects of time, temperature and peptiser concentration have also been examined, and explanations are offered for the phenomena observed.

X-ray analyses of argillaceous rocks from the Skipton anticline show that their average composition is quartz 30%, calcite 27%, feldspar 5%, illite 15%, kaolin 17%. Pyrite and other constituents account for the remaining 6 %. The quartz, calcite and feldspar are considered to be detrital, the variations in their quantity and size reflecting changes in the source of the sediments. The evidence indicates the general predominance of kaolin over illite, which is contrary to other published results on Carboniferous marine shales. A kaolin-rich source is necessary to account for the composition of the sediments. An occurrence of unusually pure and well-crystalline melanterite is recorded from the Draughton Limestone.

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 optical properties of oriented montmorillonite aggregates were measured in both non-complexing and complexing media. The changes observed lead to the following conclusions. Preparing oriented aggregates of clays for optical examination requires considerable care to avoid spurious orientation effects. In determining the optical constants of montmorillonite aggregates the medium must wet and enter the aggregate readily and displace the air, particularly from the smaller pores, otherwise large form birefringence effects of uncertain magnitude will occur. A suitable medium is likely to be one that complexes montmorillonite. The complex it forms must have relatively isotropic interlamellar layers and this is more likely with isodimensional molecules. Consideration of complexes with simple compounds suggests that the intrinsic birefringence of aggregates is overestimated by conventional techniques.

Forming complexes with aromatic compounds usually results in the birefringence of the aggregate being essentially determined by the orientation and anisotropy of the intercalated molecules.

The sorption of potassium by mica partially depleted of potassium was studied by adding potassium to a solution of sodium chloride in quasi-equilibrium with the mica. The concentration of potassium in the solution was increased 1·5 times before reverse exchange was initiated. Potassium resorbed by the depleted mica was extracted more readily than potassium from the original mica. Potassium exchange from mica is not reversible; there is irreversible change in the mica when potassium is exchanged and also an additional hysteresis in the forward and reverse exchange.

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.

Two phlogopites depleted of potassium by extraction with sodium tetraphenyl boron released resorbed potassium more readily than the original micas, but the large difference in the exchange parameters of the two micas were paralleled by those of their potassium-saturated alteration products. The apparent basal spacings of the potassium-saturated alteration products were about 0·03Å larger than those of the corresponding untreated micas; their broader lines indicate structural irregularities.

The intercalation of several highly polar organic compounds into kaolinite and the formation of interlamellar complexes has been examined by X-ray diffraction. Some compounds intercalate directly into kaolinite, while others can only be intercalated by the displacement of a previously intercalated compound. The formation of the complexes is strongly dependent on the properties of the organic compound, and generally a large dipole moment favours the formation of a complex. A large dipole moment may however cause extensive association in the liquid state and this decreases the rate of intercalation. The addition of water to highly associated compounds increases the rate of intercalation by breaking up the structure of the associated liquid, and the rate passes through a maximum with increasing water content. Thus the rate of intercalation is found to depend on the extent of association in the liquid or solution, the temperature and the molecular size. The d(001) spacings of the complexes are given and the orientation and packing of the intercalated molecules in relation to the Δ - values is discussed.

A 14 Å swelling mineral, interlayered with what is probably an organometallic complex, occurs in the surface horizon of a gleyed soil near Gartly, Aberdeenshire. The interlayer material is thermally stable at 300°C and is easily removed by oxidation with H2O2 and NaOCl. Treatment with HCl and Na2EDTA destroys the ability of the mineral to expand with glycerol, although not if the clay is H2O2 treated beforehand. The Gartly clay mineral is also unusual in that Mg-saturation, using magnesium acetate at pH 7, leads to the rapid formation of brucite-like interlayers. It is concluded that in the investigation of soil clays it is best to avoid all pretreatments.