The clay minerals formed in a deeply weathered boulder conglomerate of Middle Old Red Sandstone (Devonian) age in north-east Scotland have been studied by a variety of physical and chemical techniques. The granite and granulite boulders in this deposit are completely weathered. With the exception of microcline, all the feldspars in these rocks—orthoclase feldspar, orthoclase-microperthite, albite, and oligoclase—weather to a Cheto-type montmorillonite, poor in iron. Electron and optical microscopy indicate that the weathering transformation is a direct one, without the intervention of any intermediate crystalline or well-defined amorphous phase. Structural control of the primary mineral over the formation of the montmorillonite seems to have been a minimal factor and the evidence suggests that the clay mineral crystallized from the soluble or colloidal products arising from the decomposed feldspars. Smaller amounts of kaolinite also formed during weathering but largely from the weathering of muscovite. The environment in which these changes occurred seems to have been alkaline in a relatively closed system. Chemical analyses of related cores and weathered shells of granite and granulite bounders show only a slight decrease of silica and an increase in magnesia. Judging from the extent of alteration to secondary clay minerals, the order of resistance towards weathering of the primary minerals in these rocks is plagioclase = orthoclase < muscovite < biotite < microcline < quartz.

Dodecylammonium chloride (DAC) is used as a reagent to displace potassium from a wide range of mica minerals. Displacement is rapid and essentially complete for trioctahedral micas even in dilute solutions (0·02N DAC) at low suspension concentrations. Increasing the suspension concentration, or the concentration of potassium in the extracting solution decreased the extent to which potassium could be displaced before equilibrium was established. Under standardized conditions of temperature and suspension concentration, the rate of potassium displacement increased as the particle size decreased although complete displacement was more difficult to achieve for the finest fraction (< 2μ) than for the coarser particles.

The trioctahedral samples were shown to be more susceptible to potassium depletion by DAC than dioctahedral material. Within the range of trioctahedral samples examined the rate of reaction was found to be closely related to the fluorine content of the sample. Data obtained for the more resistant dioctahedral specimens was not sufficiently detailed to enable any similar relation to be established.

Clay beds 1–2 m thick and interbedded with marine limestones probably of early Eocene age are composed of nearly pure mixed-layer kaolinite-montmorillonite. Particle size studies, electron micrographs, X-ray diffraction studies, chemical analyses, cation exchange experiments, DTA, and TGA indicate that clays from three different localities contain roughly equal proportions of randomly interlayered kaolinite and montmorillonite layers. The montmorillonite structural formulas average K0·2Na0·2Ca0·2Mg0·2(Al2·5Fe1·03+Mg0·5)(Al0·75Si7.25)O20+(OH)4−, with a deficiency of structural (OH) in either the montmorillonite or kaolinite layers. Nonexchangeable K+ indicates that a few layers are mica-like. Crystals are mostly round plates 1/10 to 1/20 μ across. The feature most diagnostic of the mixed-layer character is an X-ray reflection near 8 Å after heating at 300°C. The clays are inferred to have developed by weathering of volcanic ash and subsequent erosion and deposition in protected nearshore basins.

An investigation of the reaction between amines and hydrogen kaolinites having a broad range of crystallinites and particle sizes has been made. Aqueous and non-aqueous adsorption isotherms, conductivity titrations, rheological measurements and sediment volume studies give strong evidence that edge sites are dominantly involved in the reaction and basal surfaces remain essentially unaltered. The acid-base reaction produces a localized adduct rather than an ionized, protonated amine. The amine-hydrate adduct adsorbs with greatly modified geometry.

Gradual change from 60% montmorillonite/40% illite randomly interstratified clay minerals at 3500 ft depth to 20% montmorillonite/80% illite at 10,200 ft can be observed in a complete section of Mesozoic shales at Barikewa in New Guinia. The top of a similar complete type Mesozoic section at 10,544 ft in the nearby Omati borehole contains 20–40% montmorillonite in randomly interstratified montmorillonite/illite. From 10,800 ft downward there is only 10–20% expandable material. Consequently depth of burial rather than stratigraphic level controls the proportion of expandable material present. Similar diagenetic alterations occur in the Wilcox Formation, Louisiana, also controlled by burial.

The amount of illite 2M polymorphs in the Papuan samples is usually less than 5 per cent, the illite 10Å peak sharpness ratio is about 1·4. Corresponding values for the Louisiana samples are 43% 2M polymorphs and about 2∙0 sharpness ratio. Chemical analysis of the Papuan shales show low MgO and K2O values when compared with the Louisiana samples. The latter sediments contain some chlorite, the former hardly any. Differences demonstrate a higher proportion of relatively unweathered material in the American samples.

Increase of chlorite content, increase of magnesium content and decrease of kaolinite content from 12,368 ft down in the Louisiana samples suggests a change in sedimentation pattern.

Large hydrothermal deposits of halloysite clay occur in the Terraced Hills, Washoe County, Nevada and similar bodies probably are present elsewhere in the Basin and Range province. The host rock, an andesitic tuff, is underlain and overlain by volcanic flows; all these rocks are late Miocene to Pliocene in age. The clay bodies are composed mostly of halloysite with some iron oxides, variable amounts of feldspar and quartz, and locally some montmorillonite. Commonly all the pyroclastic unit is altered to halloysite material. In one locality, however, the halloysite body is restricted to the upper part and it is in sharp contact with underlying, partly montmorillonitized tuff. The contact of a clay body with the overlying basalt is distinct. Generally some halloysite is present in the lower part of the basalt and montmorillonite occurs in both materials near their contact. The solutions that altered the tuff were generated during volcanism, rose along high-angle faults, and were restricted to the permeable and otherwise favorable vitric tuff by the capping of relatively impermeable basalt.

Soil samples from near Long Xuyen, South Vietnam, considered to be typical of the clayey alluvial soils of the Mekong Delta, were investigated to determine the soil mineral content and soil type. The soils are of fairly uniform composition, consisting mainly of clay minerals and quartz. the predominant clay minerals including illite and chlorite with lesser amounts of kaolinite and smectite. The small hydrous iron oxide content, indicated by fluorescence background intensity, verified that the soils are not latosols but are clayey estuarine soils amenable to future development as arable land.

The method of specimen preparation enabled direct quantitative analysis of the soil samples by X-ray diffraction with the aid of the results of mechanical analysis and of previous analyses of comparable soil samples from the Delta and nearby areas. A method for the quantitative determination of quartz was used that is independent of the powder crystallite orientation. A study of surface replicas of the soil samples by electron microscopy was made to illustrate the fabric of the soil. The undisturbed soil fabric consists mostly of somewhat randomly-oriented large domains of clay minerals with some blocky quartz particles. Nanno-fossils were present in all samples.

Coefficients of permeability, calculated using Terzaghi’s theory of one-dimensional consolidation, are reported for smectite, illite, and kaolinite, in water, methyl and ethyl alcohol, benzene, and carbontetrachloride. When the pore fluid was water the clays were homoionized to either the sodium or calcium form and the pore water electrolyte concentration was varied. The coefficients of permeability are evaluated in terms of both mechanical and physico-chemical variables. It appears that the coefficients of permeability are mainly influenced by mechanical effects, particularly the distribution of void sizes and the tortuosity of the channels. The coefficient of permeability is maximized if the flow channels consist of many small channels and a relatively few large ones, through which the main flow occurs. Physico-chemical variables exert great influence on the coefficient of permeability through their influence on dispersion or aggregation of the clay particles.

Experimental solubility data for gibbsite and kaolinite are reviewed and applied to the problem of gibbsite stability within the natural environment. It is concluded that free alumina compounds formed (only) in lateritic soils will tend to silicify spontaneously in all sedimentary environments. This metasomatic reaction should be accompanied by massive volume expansion: unusual textures are to be anticipated.

Petrographic and field descriptions of a number of ancient kaolinitic sediments (some with, some without free alumina) are reviewed. It is concluded that silicification of hydrated aluminum oxides was an important mechanism of kaolinite formation in ancient sediments and that free alumina compounds persist only as a result of the unusual volume expansion associated with kaolinite formation.

Data on montmorillonite and illite collected by A. Kahn were further analyzed to show the relationship between particle geometry and the optical density (OD) of the clay suspensions. A correction was introduced to the calculations of the minor dimension of the montmorillonite particles which took into account the volume of water between unit layers.

The assumption of disc geometry which was used by A. Kahn in the calculations of the clay particle dimension was found to be consistent with his OD measurements, thus showing that optical measurements can be used to find an equivalent radius of montmorillonite and illite when the general geometry of the particles is the same.

Ion exchange analyses of the clay-sized fraction of sediments in Lakes Pontchartrain and Maurepas suggest the selective adsorption of Na at the expense of Mg. The literature suggests that Mg should be preferentially adsorbed. As the chlorinity of the lake waters increases from 300 mg/l to 3250mg/l, the percentage of exchangeable Na increases from 13·6 to 30·6 while the percentage of exchangeable Mg decreases from 65·6–36·8. The observed exchangeable Na percentages are higher than the ones calculated from the sodium-adsorption-ratios. The difference is attributed to an increase in the Na exchange constant of the sediment and therefore an increased selectivity for Na. With an increase in chlorinity, montmorillonite increases from 47 to 61 per cent and the total of the exchangeable cations (Na, Mg, Ca, K) increases from 36 to 82 m-equiv./100 g.

A scanning and high voltage electron microscope study of the fabric of laboratory sedimented moist uncompressed kaolinite and illite floccules reveals an abundance of face-face flake orientation in the porous clay network. Clays were flocculated in the laboratory in both distilled water and slightly saline (1 g/l. NaCl) water using various clay concentrations. Floccules taken from the moist clay mass were prepared for study by freeze-drying and impregnation with polyethylene glycol.

There is little difference in the fabric of kaolinite flocculated in distilled or slightly saline water. The fabric is dominated by a 3-dimensional network of twisted chains of face-face oriented flakes having the appearance of a stair-stepped cardhouse. Illite floccules in distilled water also consist of abundant face-face oriented overlapping flakes. However, in salt water there is a more even mixture of fabrics—edge-to-face flocculation of individual platelets and also stepped clusters of face-to-face oriented flakes, the latter being more abundant.

It is suggested that under the experimental conditions the double layer of each clay particle is compressed resulting in an increase in the importance of van der Waals forces of attraction. As a result flakes approach each other and rotate into a parallel or subparallel position. The resultant dominant fabric is that of a stepped cluster of overlapping flakes.

The i.r. spectra of interlamellar kaolinite complexes with formamide, N-methylformamide and dimethylformamide have been examined. The spectra show that the amides hydrogen-bond, through the C=O group of the amide to the inner surface kaolinite hydroxyls and decrease the intensity of the kaolinite ν(OH) bands. Hydrogen-bonded kaolinite hydroxyl bands appear at lower frequencies and these have been correlated to the original kaolinite ν (OH) bands. Other kaolinite bands in the complexes show smaller perturbations of the kaolinite vibrations. Each amide hydrogen-bonds to different groups of hydroxyls. Formamide hydrogen-bonds to the 3690 and 3664 cm−1 hydroxyls, N-methylformamide to the 3690 and 3648 cm−1 hydroxyls. The interpretation for the dimethylformamide complex is less clear. The ν(NH) frequencies of formamide and N-methylformamide in the complexes are intermediate between that in dilute non-polar solution and in the liquid. This could arise from either or both a degree of intermolecular association of the amide when between the kaolinite lamellae, or to weak N—H … O hydrogen bonds to the tetrahedral oxygen sheet of the lamellae.

A review of fabric studies of clays suggests the need for relating those fabric characteristics which are revealed at the two levels of magnification provided by optical and electron microscopy, and a technique to achieve this has been developed and is described within the context of the initial stages of a long term study of the interrelation between fabric and engineering behaviour. Two kaolinitic clays with contrived fabrics were prepared by controlling particle size, moisture content and pH of suspension, and consolidation load and were subjected to shear loading to failure. Resin impregnation techniques which permit the kaolinite to be cut into thin sections for transmission electron microscopy have been optimized with the object of minimizing fabric strain and damage during ultratomy.

The fabrics of the hard and soft ambient material are qualitatively compared by means of electron micrographs and are explained in terms of the preparatory procedures adopted for fabric control. The fabrics of the two types of shear induced structures are also qualitatively compared and explained in terms of the original fabrics and the subsequent shear loading.