Swelling, shrinking and physical breakdown processes are reviewed with reference to well-known mudrock and overconsolidated clay formations in the UK and USA. Swelling results from two processes: the equilibration of depressed porewater pressures following stress relief, and the physico-chemical (osmotic) response of component clay minerals. Expansion in Na-smectite, and to a lesser extent Ca-smectite, clays is governed by double-layer swelling, whereas in kaolinites it is purely a mechanical unloading phenomenon; illites show an intermediate response. Intraparticle swelling in mudrocks older than the Silurian in the UK, or Upper Mississippian in the USA, can be expected to be reduced because of the removal of expandable layers by burial diagenesis. Shrinkage, like mudrock breakdown, is restricted to the partly saturated zone. Suction pressure-moisture content curves of indurated mudrocks are shown to be different from mudrocks and clays with high proportions of expandable clay minerals. Classification of expansion potential based on activity ratio poses problems with indurated types, but with some modification of method reasonable predictions can be made. Controls on physical disintegration are identified as: (i) incidence of sedimentary structures and discontinuities, (ii) slaking (air breakage), (iii) expandable clay mineral content, especially smectite, and (iv) clay mineral fabric orientation. Exceptionally high exchangeable sodium percentages have been measured in Coal Measures rocks susceptible to breakdown.

Clay minerals are almost ubiquitous in soil and rock and are among the most reactive silicates. They affect the engineering behaviour of soil and rock both as materials of construction and as foundation materials. In the petroleum industry, clay affects the permeability of reservoir formations, it is a common cap-rock, and it is also a constituent of the fluids used in drilling operations. Engineering behaviour almost always involves clay-water interaction and in turn this depends on the nature of water and solutions and on the composition and microstructure of the clay. The importance of clay to specific problems from each of these areas is discussed. In foundation engineering its role in soil-moisture interaction is illustrated by reference to problems resulting from the geological history of some North American soils and from engineering activities. In building materials, reference is made to its effect on concrete durability in aggregate-related problems. The importance of clay in petroleum engineering refers to authigenic clays in reservoir rocks, to clay behaviour in the Alberta oil sands and to the use of clay minerals as a geothermal thermometer.

Mineralogical analysis of Devonian Red Marl using XRD, TEM, SEM and EDAX showed that it consisted of illite, quartz, and feldspar with minor amounts of chlorite and hematite. Physico-chemical changes in the soil minerals on reaction with lime (calcium hydroxide) from one day up to two years were investigated by these techniques to gain information on the soil-lime reaction mechanism. Significant reaction of the soil minerals and lime was found to occur only at elevated temperatures (50–75°C) in a moist environment. At these temperatures, formation, growth and development of fibrous and foil-like cementitious material was observed. XRD analysis provided no strong evidence for the formation of new phases. TEM analysis and EDAX, however, showed that the newly-formed fibrous and foil-like material consisted of an amorphous calcium silicate aluminate hydrate gel, similar to the gels formed during hydrothermal treatment of lime-silica, but with lower calcium to silicon ratios than previously reported for such gels. The morphological development of the gel suggested that it formed as a result of the progressive breakdown of the clay component in the soil by reaction with the calcium ions from the lime.

Clay from the Fuller's Earth formation is shown to contain mainly illite, kaolinite and calcite, in contrast to the Fuller's Earth Bed in which montmorillonite is the main clay mineral. A negative correlation has been demonstrated between the calcite content and the plasticity as measured by the Atterberg limits. Fresh samples from the Fuller's Earth Bed have a higher plasticity than those of the fuller's earth clay with similar calcite percentages, due to the relative increases in the expanding lattice clay mineral. Weathering of the fuller's earth clay typically reduces the calcite content and increases the percentage of montmorillonite, resulting in a higher plasticity.

Geotechnical properties and behaviour are described of the very wet, halloysitic, residual clay found in the dense rain forest at Monasavu, Viti Levu, Fiji, where the annual rainfall can exceed 5 m. The tropical climatic conditions have caused deep weathering of sandstones and produced a highly plastic clay with low density and a natural moisture content greatly in excess of the standard compaction optimum. This clay was found to contain halloysite which was ‘amorphous’ rather than crystalline. The material was used in this natural state in an 85-m high rockfill dam at Monasavu Falls as an unusually soft core, the construction of which involved unconventionally light compaction by low-ground-pressure-tracked dozers. Its resulting behaviour in terms of three-dimensional total and effective stresses, stress paths and deformations throughout the construction, impounding and full reservoir stages was closely monitored. This behaviour is examined in the light of the clay's classification, mineralogical, compaction and engineering properties determined before and during construction. Despite its unusual properties, it is concluded that the clay is a good engineering material, behaving like others containing halloysite in the more common tubular form, and, moreover, that the high natural moisture content is of positive benefit.

The chemiphoresis of montmorillonite saturated with Na, K, Li or Ca was studied in a system where corrosive dissolution of Al, Fe, Zn or Cu metal plates took place in the presence of HF and H2O2. The deposition of the clay as well as metal dissolution were found to be a function of indicating that the electrochemical reaction is controlled principally by diffusion of the reacting species to the metal-liquid interface. The deposition increased with clay concentration and was lower for Ca-clay than for Na-, K- or Li-clay. It is shown that chemiphoresis alone does not provide sufficient data for the calculation of particle mobility and that other types of measurement are necessary. A relationship between particle deposition and electrical conductivity was developed, and examined experimentally with satisfactory results.

The mechanism of Ni-Mg substitution has been studied by X-ray absorption spectroscopy in phyllosilicates belonging mainly to the lizardite-nepouite and kerolite-pimelite series. Two types of information were obtained: (1) Analysis of nickel K-edge spectra under high resolution confirmed that Ni atoms were substituted for Mg atoms. There was no evidence for 4-fold coordinated Ni. (2) Extended X-ray absorption fine structure (EXAFS) was sensitive to atomic pair-correlations and gave access to the radial distribution function around Ni atoms. For all samples, this function gave two peaks. The first one was related to the (O,OH) coordination shell and analysis confirmed that Ni atoms were 6-fold coordinated. The amplitude of the second peak was very sensitive to the atomic composition of the Ni-Mg second shell. It is shown that the intracrystalline distribution of Ni is never random within the octahedral sheet; Ni atoms are segregated into domains, the minimum size of which has been calculated. In the kerolite-pimelite series the mean domain size is at least 30 Å and EXAFS could not exclude the existence of pure Ni sheets. X-ray dispersive spectroscopy combined with TEM suggested that the minerals in this series have pure Ni layers associated with pure Mg layers. In the lizardite-nepouite series, Ni atoms are segregated into specific Ni-enriched areas, the exent of which depends on the specific chemical constitution of the sample. Distribution patterns are discussed with respect to the formation mechanisms of these ore minerals.

The pore-size distribution of kaolinite has been studied by nitrogen desorption isotherms. A new method is proposed which takes account of the fact that the intraparticle or ‘internal’ area is small in comparison with the total surface area. The crystals form dihedral angles with one another, and the irregularities of the crystal edges form a slit-shaped internal pore system. When the nitrogen pressure increases, the condensed volume in the pores grows by an amount greater than predicted by de Boer's law. This excess is shown to result from capillary condensation in bevelled pores and this accounts for the main part of the intercrystalline or ‘external’ porosity. A model of condensation in bevelled capillaries has been developed and its range of validity determined.

A method is given for quantitative analysis of IR spectra of dioctahedral micas in the OH-stretching region, which involves spectral decomposition and correlation of octahedral cation contents with integrated optical densities of the corresponding bands. It provides a basis for the study of order-disorder in these minerals and has allowed revision of the crystallochemical formulae of some glauconites and celadonites.

Weathering processes in the Piedrabuena volcano, Ciudad Real province, Central Spain, have produced a smectitic phyllosilicate in four profiles on porphyritic-holocrystalline basalts consisting mainly of titaniferous augites, olivine and pigeonite. Chemical analysis of the purified smectites gave TiO2 contents of 1·89–3·77%. Apart from one profile, the smectites showed high tetrahedral Al-for-Si substitution, with the lattice charge arising from this source exceeding that from octahedral substitution, and thus could be termed beidellites. Octahedral Ti contents ranged from 0·21 to 0·41 per 24 O. A thermodynamic model was used to estimate the ΔG° of formation of these titaniferous smectites. Values ranged between −2503·30 and −2543·26 Kcal/mol. Suitable equilibria were established by calculating their ΔG° of reaction and log Ksp and, from these, the stability diagrams pH - 1/2pMg2+ against log H4SiO4 were derived. Correlations found were: (i) strong and positive between AlVI-X+ (0·91), AlIV-FeVI (0·85), AlVI-FeVI (0·85) and AlVI-MgVI (0·76); (ii) strong and negative between AlIV-octahedral charge; (iii) solubility product (log Ksp) positively correlated with X+ (0·73), AlIV (0·89), FeVI (0·67) and MgVI (0·84). Smectites showing higher tetrahedral charges were the least stable. Conversely, the stabilities of titaniferous smectites were favoured by high values of pH - 1/2pMg2+ and/or activities in soil-matrix solution. When the activities of H4SiO4 decreased, the montmorillonitic smectites became less stable than those showing beidellitic characteristics. Variations in composition and stability of the titaniferous smectites were not correlated with soil depth.

XRD analysis and electron microscopy show that hexagonal platy halloysite is the main component of an altered tuff (Ueno tuff bed) in the Pliocene Seto group, Aichi Prefecture, Central Japan. In the natural state it shows a single basal peak at 10·1 Å, which collapses to 7·2 Å, by dehydration through a segregate-type interstratification. The (02,11) non-basal band consists of slightly separated peaks which indicates moderate ordering of the crystal structure. The b-dimension is 8·936–8·939 Å. The stability of the interlayer water is intermediate with respect to halloysites of different morphologies. Between 3·5 and 4% Fe2O3 is present in the deferrated sample and the calculated chemical formula can not explain the anomalously high CEC of 21·9 mEq/100 g. Because the curvature radius and b-dimension of halloysite increase with increase in Fe2O3 content, the platy morphology is ascribed to replacement of Al3+ by Fe3+ in the octahedral sheet. Based on the geological and chemical data, the hexagonal platy halloysite is considered to have been formed from volcanic glass after deposition in a freshwater lake, where conditions were oxidizing and weakly acidic.