Using X-ray techniques, the orientation distributions of crystal planes in laboratory prepared and naturally occurring aggregates were measured. A small specimen was mounted on the axis of a goniometer and the diffracted intensity measured as the specimen was rotated. Mo radiation was used to reduce the absorption effects. A mathematical relation between the distribution of particles and the distribution of crystal planes was derived for platy and fibrous particles in flake-like and rod-shaped specimens.

When diffracted intensities of the 001 reflection of several different kaolinites were corrected for the degree of orientation in the respective specimens, a constant value was obtained. This would enable quantitative diffraction analyses to be made without the large errors that can be introduced by orientation effects. The degree of particle orientation achieved appeared to be more dependent on particle morphology than on the method of sample preparation or formation.

The complexes formed by ethylene glycol, HOCH2.CH2OH, and by glycerol, HOCH2.CHOH.CH2OH, with smectites (montmorillonite-saponite group), and vermiculites have received more attention than any other group of organo-silicate complexes. This interest arose in the first place from their use for identification purposes as proposed by MacEwan (1944, 1946) and by Bradley (1945b). Over the years, increasing attention has been given to the manner in which these complexes vary with the nature of the mineral, the magnitude and source of the charge on the silicate layers, and the number and kind of the exchangeable cations between the layers. The layer charge is determined most reliably from the full chemical analysis of a mineral, but more commonly is estimated from a measurement of cation exchange capacity.

In the last 10 years or so much work has been done to determine the crystal structures of layer silicates more precisely than previously and, as a result, ideas about these structures have had to be revised.

Around 1930 the classical studies of Bragg and his collaborators, and of Pauling, established the general geometrical features of layer silicate structures. The basic building units were found to be layers of linked tetrahedra articulated, by sharing oxygens, with layers of octahedra. In the 1 : 1, kaolinite type materials, with layer thicknesses about 7 Å, the composite layer unit was made up of one tetrahedral layer and one octahedral layer; in the mica and chlorite minerals the silicate layer was formed by joining two tetrahedral layers, one on either side, to an octahedral layer.

Urea was observed to become protonated in H-, Fe-, and Al-montmorillonite films and to form hemisalts when urea was present in excess of the number of available protons. The fully protonated urea disappeared upon dehydration, then the original protonated condition was re-established by rehydration. This completely reversible reaction indicates the importance of water in the protonated form. Indications were that urea will coordinate through the carbonyl group to the metal ion in Cu (II), Mn (II), and Ni (II) montmorillonite. Urea may be bonded to the metal ion in Mg-, Ca-, Li-, Na-, and K-montmorillonite by coordination and possibly by ionization of the N-H bond. The importance of ion-dipole interaction in urea complexes with montmorillonite is suggested. Decomposition of urea to ammonium ions was observed mainly in the Cumontmorillonite system.

One of the alteration products of a deuteric altered beryl is a high-aluminous chlorite-swelling chlorite regular mixed-layer clay mineral. An attempt was made to calculate the structural formula, and the results of X-ray, differential thermal and electron diffraction analyses are given.

The sorption of boron by clay minerals from natural waters has been studied experimentally. The quantity of boron sorbed per unit weight of clay mineral is dependent on both the salinity and the boron content of the solution. Previous work has shown that illite is the best clay mineral sorbent, though kaolinite and montmorillonite do sorb some boron and this is confirmed by the present work. The new experimental results demonstrate that the amount of boron sorbed by illite is not affected by the original boron content of the mineral and suggest that the process of incorporation of boron into the lattice proceeds in two stages. The bearing of these experimental results on the use of boron as a palaeosalinity indicator in sedimentary rocks is discussed and this leads to the conclusion that the rate of sedimentation may also influence the boron content of such rocks.

An interstratified clay mineral from Surges Bay, Tasmania, described by Cole & Carthew (1953) as containing a random stacking of illite and montmorillonite in the ratio of 3:2 and a regular stacking of illite and montmorillonite in the ratio of 1 : 1 is re-examined, after purification, and a new interpretation is made of the X-ray diffraction effects in terms of a single complex stacking model. The Fourier transform method of analysis used with an appropriate layer structure factor shows that the interstratification is produced by a three component stacking of 18% single mica layers (A), 10% double mica layers (ĀĀ) and 72% allevardite-like layers (ĀB̄) in which the A and ĀĀ layers are never together. This leads to the conclusion that the near regular interstratification of the mineral is due to structural and/or compositional variation from layer to layer within the parent crystals as suggested by Sudo, Hayashi & Shimoda (1962) to explain similar mineral types occurring in Japan.

Cretaceous and Eocene bentonites from Azerbaijan have been studied from the standpoint of their occurrence, mode of formation, and mineralogy. The bentonites are shown to be derived from the vitroclastic products of volcanic eruption by transformation in a marine environment.

Vermiculite and hydrobiotite both occur as alteration products of biotite pyroxenite near Libby, Montana. Hydrothermal and weathering studies and new chemical analyses by C. O. Ingamells suggest that the vermiculite is a product of leaching of biotite by ground waters; the hydrobiotite may be a higher temperature alteration product.

The amounts of potassium retained, after exchange with normal ammonium acetate solution at pH 7, were measured with six montmorillonite-beidellite minerals, whose interlayer charge ranged 0·72-1·00 M+/Si8O22 and where tetrahedral substitution of Al for Si ranged 0·14-0·93 M+/Si8O22. The amount of potassium retained increased with increasing interlayer charge, but there was no correlation between the amount of potassium retained and the tetrahedral charge.

Basal spacing data for neutral amine complexes with montmorillonite and vermiculite are explained on the basis of two layers of fully extended amine molecules inclined at about 65° to (001) with the NH2 groups closely associated with pairs of silicate oxygen atoms. The molecular orientation is shown to be favourable for good intermolecular packing and for possible NH..O bonding, but the results do not constitute proof of such bonding. Packing of the molecules on the silicate surfaces and with respect to each other may explain the formation of double layer complexes. The amine data are correlated with corresponding data for the low-temperature (or below melting point) series of alcohol-montmorillonite complexes and it is suggested that the molecular layers may have some solid-like characteristics.

Di- and trioctahedral micas were altered to vermiculite-like minerals by extracting the K with sodium tetraphenylboron. Chemical analysis of original and altered micas shows that loss of K is accompanied by an increased loss on ignition, oxidation of some Fe2+ to Fe3+, loss of divalent octahedral cations, mainly Mg2+, loss of OH− (or sorption of H+) and decrease in net negative charge.

The following reactions are suggested to explain these changes: (1) replacement of K by Na at interlayer sites; (2) release of structural OH− ions exposed by replacement of K, which decreases the negative charge and allows the structure to expand and more K to be replaced; (3) oxidation of Fe2+ ions by the reaction

4Fe2+ + 4 structural (OH−) + O2 → 4Fe3+ + 4 structural (O2−) + 2H2O;

and (4) release of divalent octahedral ions, possibly through some of the holes left when structural OH− is lost.

The wide implications of these proposals are discussed.

The mineralogy of the clay fractions of two soil profiles representing the end-members of a catena developed on a glacial till derived from basic lavas has been determined. Particular attention has been given to the assessment of the nature of the amorphous inorganic material in the clay fraction of these soils. Chemical dissolution techniques were used and their effects on the clay fraction were followed by X-ray diffraction, differential thermal, infrared absorption, electron-optical and surface area measurements. The principal conclusion is that the soil clays are a continuum from completely disordered, through poorly ordered to well crystallized material.

Seven samples, representative of all zones of the Upper Chalk in the Arundel area of Sussex, were treated with acetic acid and the residues analysed to determine their mechanical and mineralogical compositions. The sand and silt fractions of the residues consist mainly of flint and opaline silica, collophane, limonite, and quartz, and the clay fractions consist of montmorillonite, mica, quartz, and apatite. Authigenic apatite and quartz occur in the clay and silt and authigenic alkali feldspar in the silt. The montmorillonite may also be authigenic.

Differential thermal analysis curves were obtained for a series of diamine and glycol complexes with natural and copper substituted montmorillonite, in air and in an inert atmosphere. Thermobalance curves of the diamine-clay systems were also determined. The exothermic peaks observed in air are characteristic for any particular system and reflect the nature and binding of the interlamellar material; no direct correlation was, however, observed with pyrolysis and oxidation processes in the clay. Organic matter is frequently liberated from the clay before oxidation, which then occurs within the reaction cell but outside the clay phase. The extent to which oxidation is completed at any particular temperature depends upon the supply of oxygen and the amount of organic material present.

The crystalline swelling of sodium and potassium montmorillonites immersed respectively in solutions of sodium and potassium chloride of different concentration exhibits hysteresis in the swelling-contraction cycles. The position and extent of the hysteresis can be varied by altering the method of preparation of the clays; in all cases the hysteresis loops for potassium montmorillonite were more extensive than those for sodium montmorillonite.

The results have been explained in terms of a structural rigidity of montmorillonite crystals, where the crystals consist of five to ten aluminosilicate sheets (lamellae). The extent of hysteresis depends on this rigidity, which varies in a co-operative manner with the spacing between the lamellae in the crystal.

Electrical interactions between pairs of lamellae are also considered in analysing the swelling behaviour.

The clay mineral composition is one of the factors that affect the physical properties of soils, and a knowledge of it is required to promote a fuller understanding of the origin of these properties. The relationships between the clay content and the plastic and liquid limits of natural montmorillonitic and kaolinitic soils and of artificial mixtures have been examined and compared. Factors affecting the relationships are discussed, and illustrated by the effect of particle aggregation on the measurement of the liquid limit of tropical red clays and on the sedimentation analysis of the Keuper Marl. The effect of muscovite and of silt-sized material on the position of soils on the Casagrande classification chart has also been examined.

The removal of the alkali-soluble fraction from soil clays has been found to influence markedly the efficiency with which iron oxides can be removed from such clays. In clays pretreated with 5% Na2CO3, up to 40% more iron oxide was extracted by dithionite (Na2S2O4) than from soil clays treated with this reagent alone. Chemical analysis, electron microscopy, X-ray and differential thermal examination, and specific surface area and cation-exchange capacity measurements indicated an improved dispersion brought about by the removal of aluminosilicate binding material by Na2CO3. The electron-optical studies also showed that the dithionite-soluble iron was principally in the form of small granules. These were amorphous to X-rays and electrons and chemical analysis of the dithionite-soluble fraction suggested that they were ferruginous complexes containing considerable quantities of silica and alumina.

The industrial applications of Fullers' Earth are discussed including those of the clay in its natural form, calcium montmorillonite, and after modification by acid activation or sodium exchange. Special consideration is given to uses in oil refining, foundry bonding, civil engineering, and agriculture.