More than twenty new organic complexes of halloysite have been prepared and one hundred and twenty-seven compounds were tested. Results are compared with those of earlier studies and use is made of recent findings concerning particle morphology and interstratification effects to interpret the results. The compounds which form complexes with halloysite are polar, and are usually either acids or bases. Their molecules usually contain two functional groups (preferably —OH and/or —NH2), are relatively small and have one functional group per two carbon atoms, but do not usually include cyclic or aromatic types. The best explanation of the existence of these metastable complexes seems to lie in the ability of some organic molecules to form hydrogen bonds with the halloysite structure, about which insufficient knowledge is available to allow quantitative evaluations to be made.

Complexes formed by straight chain, primary, aliphatic alcohols from methanol to n-decanol with Ca- and Na-montmorillonite from the liquid and vapour phases, have been investigated by X-ray techniques. Satisfactory complexes are formed more readily by the Ca-mineral and from the liquid phase rather than from the vapour phase. Molecular configurations of the adsorbed molecules are suggested consistent with the experimental data. The importance of cation-dipole interactions for the lower members of the series is stressed.

Partial molal voltmae of Ca-montmorillonite, apparent molal volume of silica gel in water and of Ca-montmorillonite in ethanol-water mixtures, were determined using pycnometer density measurements. No electrostriction of water was observed with silica gel but took place in Ca-montmorillonite thus indicating the principle role of surface charges in stricting water. In ethanol-water mixtures alcohol molecules were salted out at low alcohol concentration, but they started reaching inner zones near the clay surfaces when their mole fraction in solution was increased beyond the value of 0·55.

A variety of stevensite was collected at the Obori mine, Yamagata Prefecture, Japan. Analysis shows close agreement with published data for stevensite. Chemical composition: SiO2 52·76%; A1203 trace; Fe203 0·38%; MgO 23·67%; MnO 1·57%; CaO 2·19%; Na2O 0·37%; K2O 0·00%; H2O+ 6·52%; H2O− 12·38%; Total 99·84%. The structural formula is (Fe0·04 Mg5·31 Mn0·02) Si80·1 020·00 (OH)4·00·Ca0·36, Na0·10.

This specimen shows an interstratified structure of dehydrated and hydrated layers, the former caused by dehydration of the interlayer water, although stevensite essentially contains a non-swelling layer and shows interstratification. The intensities and spacings of the 00l reflections change successively with changes in humidity. When treated with water and glycerol, the 00l reflections are similar to those of montmorillonite. The DTA and TG curves are similar to those of stevensite and an interstratified mineral of talc and saponite.

Vermiculite single crystals swell to the gel state as a consequence of treatment with concentrated solutions of γ-aminobutyric acid.

The amount of swelling was determined, by measuring by X-ray diffraction the separation of the elementary silicate layers in the gel-like crystals.

By application of pressures into the gels along the swelling direction, a direct measure of the swelling pressure is obtained. The relation between swelling pressures and equilibrium interlayer distances is a function of both cationic concentration and dielectric constant of the solution. Measured swelling pressures are consistent with a model based on formation and interaction of diffuse double layers of aminoacid cations around the silicate particles, these having a Stern layer of an approximate thickness of 5 Å. The specific chemical adsorption potential of the system has been estimated as φ = 3·3 + 0·2 Kcal/mol.

It is suggested (1) that large amounts of Al, Fe and Si carried in solution by fresh water are chemically precipitated as hydroxide gels in the brackish water environment of estuaries and deltas, and (2) that these gels are subsequently deposited in both the brackish water environment and in the neighbouring seas, where they become parental material for the neoformation of clay minerals, and various other silicate and iron minerals. The types of neoformed minerals will depend upon both the composition of the parental gels and the physico-chemical milieu of their crystallization. Evidence is discussed supporting this hypothesis from the following sources (1) the concentrations of Al, Fe and Si dissolved in fresh water and in sea-water, (2) experimental work on the crystallization of alumino-siliceous gels, and (3) a study of the precipitation of Si from the waters of the Mississippi River delta.

Because of the unusual sediment pattern of present times, this source of neoformed clay minerals and other minerals contributes only a small proportion of the sediments of the brackish parts of estuaries, deltas and the adjacent seas, which are dominated by fine-grained continental detritus. In earlier geological eras, when the world's river systems carried only relatively minor amounts of fine-grained continental detritus, this source of neoformed minerals is likely to have contributed a considerable proportion of the fine-grained sediments of these areas of sedimentation. Three possible examples are discussed.

Fixation of K by soil clays and selected reference clay minerals was induced by dry heat and hydrothermal procedures, at 100°C, 200°C and 380°C. Appreciable amounts were fixed at all temperatures. In the cases of the samples treated hydrothermally the amounts fixed increased with pressure.

Fixation by dry heating at 380°C was significantly greater than at 100°C and 200°C respectively. Fixation under hydrothermal conditions increased in order 380°C > 200°C > 100°C.

Reductions in cation exchange capacities (and surface areas) were associated with fixation, indicating that some fixation was due to ion exchange. Changes in mineralogy in some of the samples also support the conclusion that ion exchange was partly responsible for fixation. Some of the fixation under hydrothermal conditions was due to the formation of insoluble K-compounds - as for example the synthesis of a new mineral when one sample was treated.

The lattice-iron content of the clays may have influenced their hydrothermal behaviour. Thus the Princes Town Clay ( > 7-5 % lattice-iron) and three nontronites (≫ 7-5 % lattice-iron) showed appreciable lattice collapse after hydrothermal treatment, while Wyoming bentonite and hectorite (<3-5%) lattice-iron) showed no collapse at all.

The degree of crystallinity of the mineral may also have influenced its hydrothermal reaction. For example, the highly disordered soil kaolinite (St John's) was much more reactive than the more ordered Georgia kaolinite. Also, the more-ordered reference clays fixed relatively less K at 380°C than the less-ordered soil clays.

Dispersions of Laponite clay in various electrolyte solutions have been studied. In the total absence of electrolyte the synthetic clay forms a sol at 2% concentration. All cations cause gelling and flocculation.

It has been found that for any given clay concentration the yield value of the dispersions at equivalent flocculation level is the same for all electrolyte solutions, making it possible to study all types of dispersions at a standard level of flocculation.

At standard level of flocculation, the yield values have been found to follow exponential relationships with clay concentration with a break in the curves occurring at about 1·6% clay concentration. It is postulated that the break in the yield value curve occurs when enough clay is present to form a card-house structure. The plastic viscosities show a linear relationship with concentration and indicate high effective dispersed volume fractions at low clay concentrations.

When comparing the flocculating effects of different cations at fixed clay concentration, an empirical relationship has been found between cation concentration giving standard flocculation level, cation valency and radius.