The ophiolitic rocks appearing near Monte Chiaro, characterized by serpentine masses crossed by veins of talc, sometimes of remarkable thickness, are to be found on the right of the Taro river a few miles from Borgotaro. On examination three interstratified clay minerals were found: saponite-talc, chlorite-saponite, chlorite-vermiculite, which were studied optically, with X-ray, d.t.a. and chemical analysis.

Water vapour atmospheres are known to raise the temperature of the endothermic reaction of clay minerals in differential thermal analyses. In isothermal kinetic studies of dehydroxylation, it is shown that a stationary state is attained depending on the operating temperature. The rate of dehydroxylation is a function of specimen size and shape, which suggests a controlling influence by entrapped water vapour. Even at constant reaction temperatures, the rate of dehydroxylation varies greatly between the interior and the exterior of a specimen. The bearing of these results on thermal analyses and on kinetic studies generally is discussed.

Fuller's earth from near Dry Branch, Georgia, is shown by X-ray analysis to contain comparable amounts of montmorillonite and cristobalite, and only minor amounts of other minerals. The cristobalite resembles the high form, but may be a very disordered low form. Electron micrographs show the montmorillonite to be lath-like, and the cristobalite globular in form.

A method is described whereby differentiation between clay minerals may be rapidly effected. The method depends upon the differential moisture adsorption of clay minerals. There seems no reason why reasonably quantitative results may not be obtained. An application to the Etruria Marl is given.

By the employment of suitable sampling and analytical methods a marked degree of vertical variability is shown to exist in two exposures of Oxford Clay. Very little of this variation was apparent on visual examination of the strata. Some lateral variation exists between the two exposures, which are thirty miles apart, but this is on a relatively minor scale.

Trends for the vertical variation have been determined and these are in the main common to both areas. The lowest beds are high in organic content and low in acid-soluble lime, whilst higher up in the succession the amount of organic material diminishes and the percentage of lime increases. When examined in greater detail these trends are found to be more complex: they are the resultant of innumerable small scale sedimentary cycles. Thermal methods of analysis have shown that the organic material present in the lowest sixty feet or thereabouts of the Buckinghamshire succession, differs considerably in its ignition range from that found in the next twenty feet. In some respects the characteristics of the higher-level combustible resemble those of lignite. D.t.a. examination suggests that the clay mineral illite is dominant in all layers of the succession in Buckinghamshire. Some montmorillonite may be present in certain of the higher zones either as a simple impurity or in the form of an interlayering with the illite.

The effects of some aspects of these variations on the processes of Fletton brickmaking are discussed.

A method for determining the peptizability of various clay minerals is described. It is of considerable use for industrial purposes.

The mechanism whereby water is absorbed by soils and thereby causes expansion and “heave” is discussed. The dependence of expansiveness on occurrence of montmorillonitic and illitic clay types is shown. Rapid methods of analysis used, include a micro-desiccator method of deriving water vapour pressure isotherms and the technique of glycol retention.

Study of “tierras de Lebrija” by chemical, dehydration curves, d.t.a., X-ray and electron microscopic methods indicates the composition of these Pliocene sediments to be approximately equal quantities of attapulgite and illite.

The features required in a calorimeter for studying clay mineral systems are discussed and a suitable calorimeter of high sensitivity is described in detail.

Examination of the differential thermal characteristics of a normal montmorillonite saturated with a series of monovalent and divalent cations shows that the temperature of the main dehydroxylation peak is independent of valency but is apparently a parabolic function of ionic radius. NH4+, Cs+, Zn2+ and Cd2+ give anomalous results, but the apparent discrepancy of the former two ions can be fully accounted for. The results are believed to be consistent with evolution of water molecules through the hexagonal holes in the sheet surface and diffusion between the layers to the micelle edge. The significance of variation in the 800–1000°C region of the curve is briefly considered.

In soil mechanics all of the preparatory techniques relating to clay soils have been standardised. Working in all other branches of science or technology, clay mineralogists have to uncover as best they can techniques from a widely scattered literature or learn from their “older” colleagues. In the present symposium we are to hear about some of the latest methods of preparing clays especially for X-ray and electron-optical study; yet I hope that when the Editor comes to publish these valuable contributions he will also find space to refer to some of the more humble methods of preparing clays; they do not appear to have been collected together before; we know them all by name—the Truog treatment, Mackenzie's method, or the Grim gambit—but where do we find them in printc?

“First catch your clay.” Undisturbed clay samples are regularly taken by engineers and by agricultural clay mineralogists. Moisture content, bulk density and rheological properties depend upon near-perfection in the taking of these samples in the field.

A description is given of the widespread development in the U.S.S.R. of deposits of clay, largely kaolinitic in mineralogical content. These deposits also may be traced outside the U.S.S.R. Their origin is believed related to a period of intense weathering in Mesozoic times. It is pointed out that this thesis of an ancient crust of weathering would well repay application in other countries, where deposits normally regarded as of pneumatolytic origin might possibly be due to intense weathering.

The mineralogical nature of clays from the Catalan coastal range corresponding to Bunter, Muschelkalk and Keuper in stratigraphic sequence has been investigated. The predominant minerals present are illite, quartz, carbonate (calcium and/or magnesium) and chlorite in the Keuper and Muschelkalk and in the Bunter kaolinite is found in addition. Attention is drawn to the occurrence of interstratified chlorite and swelling chlorite, which association may be typical of clays deposited during Triassic time.

Cation exchange capacity (c.e.c.) determined by methylene blue can be regarded as a useful soil mechanical test in its own right. When a large number of liquid limit (LL) tests have to be done to determine variation in clays of the same general type, as on an engineering site, economy of operation could be achieved by carrying out many c.e.c. tests and few LL tests. It is only when comparing clays of widely different types that correlation is poor.

Constructional details of the balance and methods to give maximum sensitivity in obtaining and presenting results are described. Examples of work on clay minerals include comparison of results from the balance with d.t.a. traces of kaolinite and halloysite, low temperature dehydration of various montmorillonites, and a series at different rates of heating showing the relation between the d.t.a. trace and the equilibrium isobaric dehydration curve of Li+-Wyoming bentonite.

A sample of “phenyl” montmorillonite containing 10% by weight of carbon has been examined as a sorbent for nitrogen, benzene and water. The material shows only a small loss in weight on outgassing, and there is no interlamellar sorption of nitrogen and little of either benzene or water. In its behaviour as a sorbent it thus differs notably from the natural clay, from some alkyl ammonium forms of clay, and from certain “clay esters.” The small amount of interlamellar sorbed benzene is desorbed with difficulty and is sorbed only slowly. It is concluded that nearly all the interlamellar space is filled with organic material, but it is not possible to say whether this is chemically bonded or very strongly sorbed by a physical mechanism.

The methods for clay separation described involve dispersion, sedimentation, coagulation, and peroxidation. Modifications to deal with organic soils are also described.

The thermal dehydration of a series of smectites has been investigated by X-ray methods. It has been found that the rate of collapse of the layers is governed by the type of exchangeable ion present.

The high temperature changes of a new saponite have been investigated. The saponite dehydrates to talc and then to enstatite, the 5·2Å fibre axis remaining constant throughout.

A brief description is given of a vacuum distillation method which, because of the low temperatures involved, does not tend to coagulate the clay when used for concentration of dilute suspensions.