Clay mineral studies in the U.S.S.R., mainly since 1960, are summarized. Electron diffraction techniques especially have been developed and used extensively. Methods have been developed for simultaneous recording of DTA curves and other properties. Polytypism of phyllosilicates has been studied intensively by Zvyagin and others. Much new information on the structure and morphology of halloysites has been obtained by electron-optical methods. Other clay minerals extensively studied include allophanes, kaolinites, chlorites (“donbassite” is preferred to “sudoite” for dioctahedral varieties), alushtite (or tosudite), monothermite, and various zinc-bearing clays. Much attention has been given to physico-chemical and colloid-chemical properties. The natural occurrence and alteration of clays and clay minerals are described in weathering and oxidation zones, in soils, and in Recent and Ancient sediments. Primary clay minerals of hydrothermal origin are described.

Vermiculites and smectites in soils and sediments are frequently partially interlayered or “chloritized”. Dioctahedral expansible layer silicates are those most frequently interlayered, and hydroxy-Al appears to be the principal component of the non-exchangeable interlayer material.

The most favorable soil conditions for interlayer formation appear to be: moderate pH (4·6–5·8), frequent wetting and drying cycles, and low organic matter content.

In marine sediments, hydroxy-Mg interlayering may be significant. Soil-derived clays containing partially filled hydroxy-Al “brucite” sheets may be filled out with hydroxy-Mg. Under reducing conditions, hydroxy-Fe interlayers may be important.

Depending on the OH/Al ratio and Al content of hydroxy-Al interlayers, expansible layer silicate may either promote or retard the formation of gibbsite. Interlayered expansible layer silicates also may be precursors to kaolinite.

Certain clay minerals have the ability to catalyze the polymerization of some unsaturated organic Compounds (styrene, hydroxyethyl methacrylate) and yet to inhibit polymer formation from other closely related monomers (e.g. methyl methacrylate). This apparently contradictory behaviour of the clay minerals can be rationalized in terms of electron accepting and electron donating sites in the silicate layers. The electron acceptor sites are aluminium at crystal edges and transition metals in the higher valency state in the silicate layers; the electron donor sites are transition metals in the lower valency state.

The catalyzed polymerizations involve the conversion of the organic molecule to a reactive intermediate; thus where the clay mineral accepts an electron from the vinyl monomer a radical-cation is formed, where the organic compound gains an electron it forms a radical-anion. Examples of these reactions are discussed.

The inhibition of polymerization processes involves the conversion of reactive organic intermediates, such as free radicals, which have been formed by heat or radical initiators, to non-reactive entities. For example, loss of an electron from the free radical gives a carbonium ion; in some cases this will not undergo polymerization. An example of this type is the thermal polymerization of methyl methacrylate.

The color reactions on clay minerals are useful in predicting the electron accepting or electron donating behaviour of the clay minerals because they proceed by similar mechanisms to the polymerization reactions. For example, the benzidine blue reaction is a one electron transfer from the organic molecule to the electron accepting sites in the mineral (aluminium edges, transition metals in higher valency state).

Masking of the crystal edge with a polyphosphate destroys the electron accepting properties of the crystal edge; this technique can be used to control the reactivity of the mineral and to distinguish between the crystal edge and transition metal sites as electron-acceptor sites in the clay minerals.

Dickite and kaolinite are polymorphs of Al4(Si4O10)(OH)8. Dickite traditionally is regarded as hydrothermal, based on field and laboratory evidence. Dickite and kaolinite occur in cavities in phylloid algal limestones, in interstices of biocalcarenites and sandstones, and along joints, fractures, and stylolites, in Pennsylvanian rocks exposed throughout 9600 square miles of southeastern Kansas. The stratigraphic interval of approximately 1100 ft extends from the Fort Scott Limestone (Desmoinesian) through the Lecompton Limestone (Virgilian). The best crystallized dickites are found in porous algal limestones as pockets of glistening white powder composed of well developed pseudohexagonal plates up to 40 μ across. Very well crystallized kaolinites occur similarly, except the crystals are much smaller. Less well crystallized dickites and b-axis disordered kaolinites occur in less porous rocks. Variations in crystal size and morphological development are genetically significant.

Dickite-kaolinite distribution is related to: (1) stratigraphic alternation of limestones and impervious shales; (2) gentle, westward regional dip; (3) thick, mound-like buildups of highly porous algal limestones, miles in length and width; (4) igneous intrusions (early Tertiary?) in Woodson and Wilson counties. Dickite is confined to an elliptical area 125 miles long northeast-southwest, extending 60 miles eastward from the intrusions. Dickite is associated preferentially with porous algal mounds. Kaolinite occurs in less porous rocks within the dickite area, and also is abundant well beyond. Heated groundwaters, possibly mixed with magmatic waters, moved readily up-dip and along strike outward from the intrusions through the conduit-like algal mounds; dickite was deposited from such solutions. Where water movement was restricted or where water had travelled tens of miles from the intrusions, water temperature fell below the limit for dickite crystallization, and kaolinite precipitated instead. Kansas dickite, unlike most other reported dickites, formed in rocks that were neither deeply buried nor extensively altered hydrothermally.

A ternary plot of the tetrahedral R3+ and octahedral R3+ populations for the dioctahedral 2:1 clay minerals shows a broad range of compositional variation within each of the major clay minerals. The clay minerals can be subdivided on the basis of total charge, location of the charge, and the relative amounts of Al and Fe3+ in the octahedral sheet. The division is natural and is controlled by the misfit between the tetrahedral and octahedral sheets and the need for tetrahedral rotation. The compositions of the tetrahedral and octahedral sheets are interdependent. Whereas muscovite has a lower limit of 1·7 Al octahedral occupancy, illite and montmorillonite have a lower limit of 1·3 Al; lower Al values result in the formation of a chain structure.

Interlayers were produced in montmorillonite, vermiculite and hectorite in aqueous suspensions by precipitation from metal chloride salt, by hydrolysis of metal amalgams, and by slow hydrolysis of metal acetate during refluxing. In several systems an external phase of bayerite, gibbsite, or brucite was also formed. A prominent high frequency OH stretching vibration is associated with the interlayer in montmorillonites with approximate frequencies of 3660 cm−1 with nickel interlayers, 3690 cm−1 with aluminium interlayers and 3710 cm−1 with magnesium interlayers. Pleochroism studies indicate transition moment of interlayer OH to be at a relatively high angle to the planar surface of the clay crystals. Aluminium interlayers show some evidence of an additional weak absorption in the lower frequency region of 3570–3600 cm−1. In differential studies the lower frequency absorption is more evident and is shown to be unaffected by orientation. Techniques involving balancing of water deformation bands in differential spectra and D2O exchange suggest that it is not a water band. D2O flushing to remove water leaves the low frequency interlayer OH band more prominent in hectorite where the clay crystal OH is at 3680 cm−1. Deuteration studies show that flushing with D2O at room temperature removes water, and heating at 100°C in D2O vapor exchanges interlayer OH but not the clay crystal OH. Study of the OD stretching of the systems with deuterated interlayers supports observations made in the OH stretching bands.

Previous investigations have demonstrated the influences of interlayer cation composition, relative humidity, temperature, and magnitude of interlayer surface charge on the interlayer hydration of montmorillonites and vermiculites. It has been suggested that the sites of layer charge deficiencies may also have an influence upon the amount of hydration that can take place in the interlayers of expandable clay minerals, if the interlayer cation-to-layer bonds are considered as ideally electrostatic, the magnitude of the forces resisting expansion may be expressed as a form of Coulomb’s law. If this effect is significant, expandable structures in which the charge-deficiency sites are predominantly in the tetrahedral sheet should have less pronounced swelling properties than should structures possessing charge deficiencies located primarily in the octahedral sheet.

Three samples that differed in location of layer charge sites were selected for study. An important selection criterion was a non-correlation between tetrahedral charge sites and high surface-charge density, and between octahedral charge sites and low surface-charge density.

The effects of differences in interlayer cation composition were eliminated by saturating portions of each sample with the same cations. Equilibrium (001) d values at controlled constant humidities were used as a measure of the relative degree of interlayer hydration.

Although no corrélation could be made between the degree of interlayer hydration and total surface-charge density, the investigation does not eliminate total surface-charge density as being significant to the swelling properties of three-sheet clay-mineral structures. The results do indicate a correlation between more intense expandability and predominance of charge deficiencies in the octahedral sheet. Conversely, less intense swelling behavior is associated with predominantly tetrahedral charge deficiencies.

Surface area determinations were made on a montmorillonite with various cations emplaced on the exchangeable sites, utilizing nitrogen and carbon dioxide as adsorbates at 77°K and 195°K, respectively, in a dynamic system. From the fraction of a Mississippi montmorillonite less than about 1 μ in size, samples were prepared by replacing the original exchangeable cations with Li+, Na+, K+, Rb+, Cs+, Mg++, Ca++, Ba++, and NH4+, forming a series of homoionic montmorillonite species.

Surface areas from 3-point B.E.T. plots (half-hour adsorption points), with nitrogen as the adsorbate, ranged from 61 m2/g for Li-montmorillonite to 138 m2/g for Cs-montmorillonite, thus reflecting a certain degree of nitrogen penetration between layers. Complete penetration should theoretically result in a surface area of over 300 m2/g for this clay with a nitrogen monolayer between each pair of platelets. The experimental data indicate that the extent of penetration is time-dependent and is also a function of the interlayer forces as governed by the size and charge of the replaceable cation. This finding negates the generally accepted concept that nitrogen at 77°K does not penetrate the layers and provides a measure only of the external surface of expandable clay minerals.

A further measure of the variation of interlayer forces is provided by the adsorption of carbon dioxide at 195°K. Surface area values ranged from 99 m2/g for Li-montmorillonite to 315 m2/g for Cs-montmorillonite. Although the carbon dioxide molecule is larger than the nitrogen molecule, its greater penetration apparently is a result of its being kinetically more energetic (with a larger diffusion coefficient) at its higher adsorption temperature. Similar differences have been found with both adsorbates in the study of microporous substances, such as coal, where activated diffusion is of considerable significance.

The pyridinium-montmorillonite complex has the ability to sorb additional aromatic molecules between the layers. The neutral molecules occupy the vacant space produced by the change in orientation of the pyridinium ion from a parallel to a perpendicular position and with the N-H group directed toward the negative unit layer surface.

In favorable cases the orientation of the additional neutral molecules can be ascertained by infrared spectroscopy. Examples of this analysis are presented in the complexes of pyridinium-montmorillonite with chlorobenzene. The molecules adopt a vertical orientation but with the halogen bond axes parallel to the layers.

Seventy-four samples from eight stratigraphic sections of lower Pleistocene glacial and glaciofluvial deposits in Doniphan County, extreme northeastern Kansas, were analyzed using X-ray diffraction techniques. Clay-mineral) assemblages of the <2 μ fraction of these deposits are nearly identical, consisting of a mixed-layer clay mineral associated with minor amounts of kaolinite and illite.

An attempt was made to differentiate units of till and nontill deposits by using the relative intensities of 001 reflections of “mixed-layer mineral,” kaolinite, and illite. At least two tills were recognizable. Associated nontill deposits, could not be differentiated from one another, although the nontills are easily distinguished from tills.