The morphology of volcanic glass particles in rhyolitic and andesitic tephra of central North Island and Taranaki areas of New Zealand has been studied by scanning electron microscopy. Electron probe analyses of the glasses are compared with those of the clays to which they weather. Loss of silica characterizes the weathering of both glasses. The rapid rate of weathering of andesitic glass is attributed to its occurrence as fine, soft microlites and extensive substitution of Al for Si in the structure. Rhyolitic glass weathers more slowly because it occurs as hard and brittle particles containing relatively little alumina. It is suggested that the structure, chemical composition and chemical activity of allophane is governed largely by the chemical composition and bonding characteristics of the parent glass.

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.

The principal clays of the northern and central North Sea are illite (sometimes with interlayered smectite) and kaolin. Chlorite is only locally important. Although it has been proposed that kaolin within North Sea sandstones is detrital in origin, the majority of workers have concluded that it is authigenic, largely the product of feldspar alteration. Kaolin is found within a wide range of sedimentary settings (and within shales) apparently defying the notion that kaolin is an indicator of meteoric water deposition. Within sandstones, the earliest authigenic kaolin has a vermiform morphology, the distribution of which is controlled by the availability of detrital mica to act as a nucleus, and the composition of the post-depositional porewaters. This vermiform kaolin formed in meteoric water, the presence of which is easily accounted for below sub-aerial exposure surfaces in non-marine formations, and below unconformities over marine units. In fully marine sands, and even marine shale units, kaolin still occurs. It has therefore been suggested that even these locations have been flushed with meteoric water.

Early vermiform kaolin recrystallizes to a more blocky morphology as burial proceeds, at least in the Brent Group. Blocky kaolin has been reported as growing before, synchronously with, and after the formation of quartz overgrowths, though oxygen isotope studies support low-temperature growth, pre-quartz. Blocky kaolin may form during meteoric flushing associated with lower Cretaceous uplift and erosion, though it is found in fault blocks that are thought to have remained below sea level. Here, the kaolin may form in stagnant meteoric water, relics of the post-depositional porewater. It has also been proposed that the blocky kaolin grew in ascending basinal waters charged with carboxylic acids and CO2, though this hypothesis is not supported by stable oxygen isotope data. Some of the blocky kaolin is dickite, the stable polymorph above ∼100°C.

Fibrous illite occurs almost ubiquitously within the clastic sediments of the North Sea. An early pore-lining phase has been interpreted as both infiltrated clastic clay, and as an early diagenetic phase. Early clays may have been quite smectite-rich illites, or even discrete smectites. Later, fibrous illite is undoubtedly neoformed, and can degrade reservoir quality significantly. Both within sandstones and shales, there is an apparent increase in the K content deeper than 4 km of burial, which could be due to dilution of the early smectite-rich phase by new growth illite, or to the progressive illitization of existing I-S. Much of the ‘illite’ that has been dated by the K-Ar method may therefore actually be I-S.

The factors that control the formation of fibrous illite are only poorly known, though temperature must play a role. Illite growth has been proposed for almost the entire range of diagenetic temperatures (e.g. 15–20°C, Brent Group; 35–40°C, Oxfordian Sand, Inner Moray Firth; 50–90°C, Brae formation; 100–110°C, Brent Group; 130–140°C, Haltenbanken). It seems unlikely that there is a threshold temperature below which illite growth is impossible (or too slow to be significant), though this is a recurring hypothesis in the literature. Instead, illite growth seems to be an event, commonly triggered by oil emplacement or another change in the physiochemical conditions within the sandstone, such as an episode of overpressure release. Hence fibrous illite can grow at any temperature encountered during diagenesis.

Although there is an extensive dataset of K-Ar ages of authigenic illites from the Jurassic of the North Sea, there is no consensus as to whether the data are meaningful, or whether the purified illite samples prepared for analysis are so contaminated with detrital phases as to render the age data meaningless. At present it is unclear about how to resolve this problem, though there is some indication that chemical micro-analysis could help. It is a common belief that illite ages record the timing of oil charge, and so can be used to calibrate basin models.

Grain-coating Fe-rich chlorite cements can preserve exceptional porosity during burial. They are found in marginal marine sandstones, formed during diagenesis from precursor Fe-rich clays such as berthierine or verdine.

The Boom Clay is an important raw material for the Belgian structural clay products industry. It can be divided into several lithological sub-units. In order to obtain an insight in the parameters which characterize these different units, and which affect the overall properties of the clay, a detailed chemical, physical and mineralogical analysis was carried out. Pearson correlation coefficients were calculated between the variables, which were then placed in four correlation groups: a quartz/clay mineral group, a reducing component group, a carbonate group and a feldspar group. This treatment of the data allowed three analysis parameters to be selected: <2 µm fraction, organic carbon and CO2. The other variables could be calculated fairly accurately from these by means of regression lines.

Measurements of the kinetics of acid dissolution of synthetic aluminous goethites and corresponding hematites produced by heating of parent Al-goethites at various temperatures were carried out in 1 M HC1 at 30, 40 and 50°C. Dissolution-time curves show sigmoidal shapes for the goethites (110°C), whereas deceleratory shapes were obtained for most of the partly and fully dehydroxylated samples. The dissolution rate for all materials decreased with increasing Al substitution and increased with increasing dissolution temperature, specific surface area and heating temperature. On a unit surface area basis, hematite dissolved ∼ 2–8 times faster than goethite. Dissolution kinetics of most heated goethite samples (200–260°C) were quite well described (R2 > 0.96) by the modified first-order Kabai equation. The activation energy and frequency factor for dissolution increased with increasing Al substitution.

Resonance Raman spectroscopy has been used to observe the formation of cation radicals in the adsorption of N,N,N',N'-tetramethylbenzidine (TMBD), benzidine, N,Ndimethylaniline (DMA) and aniline on Na-, Cu- and Fe-montmorillonites. Cation radicals of benzidine and TMBD, and their dications were formed at acid sites on the montmorillonite surface, or through the reduction of Cu or Fe interlayer ions, and were adsorbed in the interlayer. Their structures are represented by biphenoquinone type structure, where the inter-ring CC bond and the ring C-N bond have double bond characters. It was demonstrated from Raman spectra that DMA and aniline adsorbed on Cu-montmorillonite from the vapour phase dimerize to form TMBD and benzidine dications.

Three clay samples (a kaolinite, a halloysite and an inseparable mixture of kaolinite-palygorskite-illite-montmorillonite) were, after a mild pretreatment, successfully tested as catalysts in the polymerization of styrene. The catalytic activity of the clay (measured by the conversion rate), the MW and the colour of the polystyrene obtained depended not only on the chemical composition and the structure of the clay catalyst but also on its concentration in the medium. The polystyrenes obtained on the clay catalyst were composed of two groups of macromolecules, one with low MW and the other with high MW.

Two soil profile sequences on paragneiss debris in the Val di Rabbi (Northern Italy) along an altitude gradient ranging from 1200 to 2400 m a.s.l. were studied to evaluate the effect of aspect on the weathering of clay minerals. All the soils had a coarse structure, a sandy texture and a low pH. Greater weathering intensities of clay-sized phyllosilicates (greater content of smectites) were observed in soils on the north-facing slope. On the south-facing slope, smectite was found only in the surface horizon of the soil profile at the highest altitude. Hot citrate treatment of north-facing soils revealed the presence of low-charged 2:1 clay minerals, the expansion of which was hindered in the untreated state by interlayered polymers. However, the hot citrate treatment encountered some problems with the samples of the south-facing soils: as confirmed by Fourier transform infrared spectroscopy, the hot citrate treatment was unable to remove all interlayer Al polymers. The 2:1 phyllosilicates were not expanded by ethylene glycol solvation in several samples, although thermogravimetric analyses indicated the presence of clay minerals with interlayer H2O. At the same time, the collapse of clay minerals to 1.0 nm following K-saturation was evident. Theoretically, this should indicate that 2:1 phyllosilicates had no evident substitution of trioctahedral cations (Mg2+, Fe2+) by dioctahedral cations (Al3+ and Fe3+). X-ray diffraction analysis of the d060 region and determination of the layer charge of clay minerals by the long-chain (C18) alkylammonium ion, however, did not confirm this. A transformation from trioctahedral to dioctahedral species was observed and low-charge clay minerals (ξ ~0.30) were identified in the surface horizons of the south-facing sites. In the south-facing soils, the podzolization process was less pronounced because of a lower water flux through the soil and probably less complexing organic molecules that would remove the interlayer polymers. Besides the eluviation process, clay minerals underwent a process of ionic substitutions in the octahedral sheet that led to the reduction of the layer charge. This process was more obvious in the north-facing sites.

Partial chemical and X-ray analyses of specimens taken serially from three different rock types from the St. Austell granite show that potash feldspar is hydrothermally altered to a micaceous mineral. Sodic plagioclase alters to mica, montmorillonite and kaolinite. Furthermore, in the latter case the micaceous mineral and montmorillonite are intermediate products between feldspar and kaolinite. It is believed that the level of H+ ion activity in the altering solutions controlled the removal of alkalis, Al2O3 and SiO2 so as to leave appropriate concentrations of these constituents to re-form as mica or montmorillonite. Further alteration of a similar kind produced kaolinite.

Microstructural (fabric, forces and composition) changes due to hydrocarbon contamination in a clayey soil (glacial till) were studied using scanning electron microscopy (microfabric analysis), atomic force microscopy (force measurement) and a sedimentation bench test (particle size measurements). Non-polluted and polluted glacial till from NE Poland (in the area of a fuel terminal) were used for the study. Electrostatic repulsive forces in the polluted samples were much lower than in non-polluted samples. In comparison with non-polluted samples, the polluted samples exhibited lower electric charge, attractive forces on approach and strong adhesion on withdrawal. The results of the sedimentation tests indicate that clay particles form larger aggregates and settle out of the suspension rapidly in diesel oil. In non-polluted soil, the fabric is strongly aggregated – dense packing, dominating face-to-face and edge-to-edge types of contacts, clay film tightly adhering to the surface of larger grains and interparticle pores are more common. In polluted soil the clay matrix is less aggregated – loose packing, dominating edge-to-face types of contacts and inter-micro-aggregate pores are more frequent. Substantial differences were observed in the morphometric and geometrical parameters of the pore space. The polluted soil micro-fabric proved to be more isotropic and less oriented than in non-polluted soil. The polluted soil, in which electrostatic forces were suppressed by hydrocarbon interaction, displays more open porosity and larger voids than non-polluted soil, which is characterized by the occurrence of strong electrostatic interaction between the clay particles.

A hydrothermal synthetic study on the relationship between the stability and the composition of sodium saponite solid solutions revealed that a special trioctahedral sodium smectite can persist stably up to temperatures as high as 850°C under a water pressure of 1 kb. This smectite has a composition close to Na0·55(Mg2·70Al0·30) (Si3·15Al0·85)O10(OH)2. nH2O as estimated from the chemical composition of gels that yield this smectite in essentially pure form at the highest temperatures, and from other phase evidence. The composition range of these trioctahedral sodium smectites and phase relationships around the smectite field in the system Na2O-MgO-Al2O3-SiO2-H2O are also briefly described in the temperature range 600–800°C under a pressure of 1 kb.

The characteristic structural, textural and compositional features of the various kaolinite-rich clayrocks known as flint clay, toasted clay, kaolinite tonstein and bauxitic clay are briefly reviewed together with their mode of occurrence. It is considered that these rocks have much in common; sufficient to warrant their grouping in a single sedimentary facies. The origin of these clayrocks is discussed and it is concluded that whereas some modifications apparently took place within the depositional area, the concept of development in Situ for the bulk of the material is difficult to substantiate. Rather, the evidence appears consistent with an essentially allochthonous origin.

The adsorption of the cationic dye acridine orange (AO) by Na-saponite and the colloidal properties of the aqueous suspension were investigated by visible spectroscopy and XRD. The organic cation is adsorbed by the mechanism of cation exchange. When small amounts of the dye are adsorbed, the system contains small tactoids and is peptized. At this stage the dye penetrates into the interlayer space and most of it undergoes metaehromasy due to interactions between the aromatic entity and the oxygen plane of the clay. When greater amounts of AO are adsorbed, the clay platelets flocculate to form book-house floes which, with excess AO, are transformed into card-house floes. At this stage metachromasy results from the aggregation of the dye in the interparticle space of the floes, in addition to the π interactions with the oxygen plane. In excess AO, the clay is gradually peptized. At this stage the dispersed clay platelets form small tactoids with monomeric AO in the interlayer space and at the same time adsorb dimerie and polymeric AO cationic species at the solidliquid interface.

In recent years, the availability of high-field superconducting magnets complemented with mechanical spinning of the samples (magic-angle spinning technique) has resulted in a considerable improvement in resolution of NMR spectra and has widened the use of this technique in the structural analysis of solid samples. In particular, NMR spectroscopy can distinguish the different chemical environments of tetrahedrally coordinated silicon and also determine short-range order in the distribution of Si and Al in micas (Sanz et al., 1983) and zeolites (Fyfe et al., 1983; Klinowski et al., 1982).

For aluminium (I = 5/2), the existence of strong quadrupolar interactions means that, in general, only the m½↔m−½ transition is observed. However, the signal is broadened by second-order quadrupolar effects, dipolar interactions and chemical shift anisotropies.

MX-80 is a bentonite clay from the Clay Spur bed, Wyoming, USA, consisting of ~80 wt.% Na-rich montmorillonite and is a leading candidate material for use in engineered barriers within underground nuclear waste disposal sites in Switzerland and Sweden. The diffusive invasion of groundwater into the engineered barriers is likely to cause the dry high-density bentonite to swell and evolve into a less-dense, water-rich gel during re-submergence of the shafts and galleries. Data on H20 diffusivity within water-rich bentonite gels are therefore essential to the safe design of the engineered barriers. To address this need, the self-diffusion coefficient, D, of 1H2O molecules in water-rich MX-80 bentonite gels was measured using the pulsed-gradient spin-echo method of 1H nuclear magnetic resonance spectroscopy at 0.47 T; D was measured over a wide range of temperatures (20.6–70.1°C) and of bentonite volume fractions (0 to 17.2 vol.%). The results showed that D increased markedly to values of bulk water self-diffusivity as the bentonite volume fraction decreased towards 0 vol.%. The activation energy of the diffusion process for the gels was approximately equal to that for bulk water. As a result, the normalized H20 self-diffusivity, D/D0, was approximately independent of temperature, where D0 is D in bulk water. The D/D0 data for ≤6.39 vol.% bentonite fraction were successfully fitted to a porous clay gel model that involves unbound water molecules that diffuse in the pore space by avoiding randomly placed discoidal obstacles (clay particles) of a high aspect ratio. The D/D0 data for MX-80 were similar to data for SWy-2 (Wyoming bentonite from the Newcastle formation) and Kunigel-Vl (bentonite from Yamagata, Japan), suggesting that all three bentonites are equally suitable candidate materials, in terms of water diffusivity performance, for use within engineered barriers.

A scheme is presented for the semi-micro analysis for the major elements in clay minerals, based mainly on improvements to conventional colorimetric methods. Silica and alumina are determined after fusing a 50-mg sample with sodium hydroxide. Titanium, total iron, calcium, magnesium, phosphorus and manganese are determined colorimetrically on a hydrofluoric-sulphuric acid digest of a 50-mg sample; sodium and potassium are determined flame photometrically on the same digest. Ferrous iron is determined separately. Additional methods for the determination of total water, total sulphur and fluorine are indicated.

Weathering processes have been studied in a podzol profile developed on sand during a postglacial period of 9400 years. Due to disintegration of rock fragments, the particle-size distribution has changed markedly in the upper part of the profile, and minerals have been transferred from sand fractions to silt and clay fractions. The most important weathering processes are the total breakdown of trioctahedral chlorite and biotite, and the transformation of dioctahedral mica (muscovite-phengite) to a regularly interstratified mineral, and further to Al-vermiculite or smectite. By using quartz as an internal standard, the annual loss due to weathering was found to be 3·2 g/m2. The release of elements due to silicate weathering was calculated from depletion curves, and the average annual release of Na + K + Mg + Ca for the postglacial period was 19 mEq/m2.

Lower Cretaceous (AJO and AJR) and Oligocene clays (AS) from northern Tunisia were analysed to evaluate their possible use in the production of earthenware tiles by dry processing and fast double-firing. The Cretaceous clays are carbonate-rich (AJO = 20%, AJR = 12%) while the Oligocene ones are carbonate-free. This led to noticeable differences in firing behaviour (shrinkage, sintering rate and loss on ignition) and consequently in functional properties (water absorption, mechanical strength, porosity). The AJO firing shrinkage is very small, which makes this clay suitable for rapid firing. The clays are illite-kaolinite-rich but the AS sample is mostly smectitic (44%) and so is used (10 wt.% maximum) only to adjust the consistency of the powder during pressing. The average agglomerate size ranges from 100 to 350 μm and the distribution is suitable for easy pressing of powders without any special need for further adjustments. Characterization of fired products confirms the high potential of these clays since all properties fall within the ceramic International Standards (ISO). For both technical and economic reasons dry processing is recommended for production of earthenware tiles, in particular for countries in sunnier climates, where solar energy can be exploited for clay drying.