The value of peak width at half-height for the illite 001 XRD reflection is known as the Kubler index or the illite ‘crystallinity’ index. This measurement, which has been related to the degree of metamorphism of very low-grade, pelitic rocks, is a function of at least two crystal-chemical factors: (1) illite X-ray scattering domain size; and (2) illite structural distortions (especially swelling). Reynolds' NEWMOD computer program is used to construct a grid with which these two contributions to illite peak width can be determined independently from measurements of the 001 peak width at half-height and the Środoń intensity ratio. This method yields more information about changes undergone by illite during metamorphism than application of the Kubler index method alone.

The kaolin minerals in lateritic weathering profiles on dolerite and granite in Western Australia have been characterized by intercalation tests for halloysites, and also by their particle morphologies. Towards the surface of the profiles there is a decrease in both total kaolin mineral content, and in the expandibility of those minerals to intercalation. Tubular kaolinite that is non-expandible by any of the intercalation tests for halloysite was identified in the upper few metres of both profiles. Hydrated halloysite is most common at the base of both profiles. Formamide expands some anhydrous kaolin minerals while the sequence of hydrazine/water/glycerol (HWG) expands more of these minerals. Non-tubular (subhedral to sub-hexagonal platy) kaolinite is also present. Hydrated tubular halloysite apparently alters to tubular kaolinite via dehydrated halloysite that is expandible by formamide and a tubular ‘kaolin’ that is expandible by HWG but not by formamide.

Analysis of the smectite content of mixed-layer illite/smectite minerals in 4 wells in the Paris Basin indicates that the sediments have not experienced the same thermal history throughout their burial history. Reconstruction of the total burial depths and thermal maxima for the sediments in the different levels of the wells indicates that the present-day depth-temperature relations reflect the existence of the same continuous sequence of diagenetic change in 2 of the wells. An empirical relation giving smectite content as a function of maximum paleotemperature was derived. A strong break in the clay mineral compositions in the upper levels of 2 wells at a third site indicated an anomaly in the diagenesis process. This break in the sequence of clay diagenetic transformation can be traced to major subvertical faults which cross-cut the wells. These anomalies are attributed to the faults which are assumed to have acted as thermal drains towards the surface, locally increasing the temperature of the sediments for a major portion of the burial history when the faults were active. Closure of the fault system coincides with the return to a normal pattern in clay diagenesis for sediments in the upper portions of the wells. It is concluded that clays may be used to trace thermal histories of sediments in a sedimentary basin.

The aim of this study was to determine the influence of the various source areas on the Neogene sediments of the Alpujarran Corridor, to ascertain the type and intensity of the sedimentary processes involved, and to establish some generally applicable criteria. At the bottom of the sections the detrital pebbles are derived from the highest nappes of the Alpujárride Complex, whereas those at the top are from the deepest unit of the Nevado-Filábride Complex (the Veleta nappe); between these the entire range of materials from the lower-Alpujárride Complex and the upper-Navado-Filábride Unit (the Mulhacén nappe) is represented. Comparison of the micas and chlorites in the pebbles with those in the conglomerate matrix reveals the effect of the sedimentary processes on every aspect of the crystallochemistry. The d001 of the chlorites and the b0 of the micas are scarcely affected and can be used to determine the source area. The crystallinity, the Fe content of the chlorites and the basal spacing and angular difference (Δ2θ M-P) of the white micas, on the other hand, are all modified, especially in the clay fraction, according to the degree and nature of the alteration of the sediments, and consequently can be used as a guide to the extent of this process.

The formation of kaolinite from Al hydroxy interlayered Garfield nontronite has been carried out at 225°C in hydrothermal conditions. The kaolinitization process, which proceeds through mixed-layer kaolinite/smectite intermediates, was followed by XRD, IR and ESR spectroscopy, chemical analysis and charge properties. The smectite content of the clay products decreases regularly with the duration of the hydrothermal treatment. The CEC and the structural Fe content of the deferrated products show a similar trend. IR features specific to nontronite disappear and are barely detectable as the smectite content of the mixed-layer clay falls below 30%. In contrast, the ESR spectrum of nontronite is characterized by a broad g2 signal that remains even after prolonged hydrothermal treatment. The calibration of the g2 ESR signal, due to Fe-smectite, shows that the synthetic kaolinites have low Fe contents (∼ 1% Fe2O3) indicating that the kaolinitization process involves destruction of the 2:1 layers and the subsequent neoformation of kaolinite and Fe oxides. As illustrated by the study of deferrated soil clay samples, representing a weathering sequence Fe-smectite → kaolinite + Fe oxides, ESR spectroscopy proved to be a powerful Fe probe for detecting Fe-rich smectite in kaolinite/Fe-smectite mixed-layer clays.

Short-chain alkylammonium derivatives of montmorillonite (< 8 or 10 C atoms in the alkyl chain) adsorb alcohols in the micropores between the alkylammonium ions. The external surface area and the micropore volume are derived from comparison plots of ethanol and butanol adsorption isotherms. The micropore volume varies between ∼0 (decylammonium derivative) and 100µl/g (methylammonium derivative); the external surface area determined by ethanol and butanol gas adsorption is about 50 m2/g, and is almost independent of the alkyl chain length. In contact with the alcohols, the alkylammonium ions in the interlayer space remain in h1 or h2 arrangement (monolayers or bilayers of flat-lying alkylammonium ions); on the external surface they move into an upward position. The heat of immersion decreases strongly with increasing alkyl chain length to a minimum for decylammonium ions, the variation being very similar for ethanol, butanol, hexanol, octanol and decanol. Immersion in ethanol increases the external surface area at the expense of the internal surface area. In butanol and longer alcohols this area remains unchanged. The increase of the external surface is related mainly to changes in the less ordered regions around the core of the crystals which consists of coherent silicate layers. The heat of wetting is ∼ 110 mJ/m2 (external and internal surfaces). The integral enthalpy of adsorption of butanol, 40–50 kJ/mol, is independent of the alkyl chain length (nc ≤ 8).

Glutamic acid deamination was realized in the absence and in the presence of montmorillonite saturated with various metallic cations (Na+, Mn2+, Cu2+). The catalytic activity depends upon the interlayer exchangeable cation and the pH of the suspension. A maximum was observed near pH = 5–6. In the presence of the enzyme l-glutamate dehydrogenase and the coenzyme nicotinamide adenine dinucleotide, glutamic acid transforms into α-ketoglutaric acid, but in the presence of montmorillonite, it yields α-hydroxyglutaric acid and traces of butyric acid. However, kinetic and reaction yield are significantly reduced compared to the biological system.

The chemical composition of the pyroaurite-type compound Fe(II)Fe(III) hydroxy-carbonate (‘green rust’) synthesised from freshly precipitated ferrihydrite and Fe(II) chloride solution at pH 7.0 (‘induced hydrolysis’) was determined. The compound was nearly stoichiometric, with the formula the Fe(II):Fe(III) ratio being independent of the Fe(II):Fe(III) ratio in the initial reaction mixture. It shows all the XRD peaks reported for this compound. Visible-near IR shows a broad peak at 650 nm which is ascribable to intervalence charge transfer and therefore the absorbance maximum decreases with increasing degree of oxidation. Wetting the material with compounds containing hydroxyl groups (such as glycerol or glucose) retards the oxidation of the otherwise very oxidation-sensitive compound. Similar polar organic compounds may stabilize the Fe(II)Fe(III) hydroxy-carbonate in wet soils. The importance of the green rust phase as an intermediate in the formation and transformation reactions of oxides and oxyhydroxides of iron in natural environments should not be ignored.

Luminescence, induced by dehydration and by wetting with hydrazine and unsymmetrically substituted hydrazine, and related ESR spectra have been observed from several kaolinites, synthetically hydrated kaolinites, and metahalloysites. The amine-wetting luminescence results suggest that intercalation, not a chemiluminescence reaction, is the luminescence trigger. Correlation between dehydration-induced luminescence and g = 2 ESR signals associated with O−-centres in several natural halloysites, and concurrent diminution of the intensity of both these signal types as a function of aging in two 8.4 Å synthetically hydrated kaolinites, confirm a previously-reported relationship between the luminescence induced by dehydration and in the presence of O−-centres (holes, i.e., electron vacancies) in the tetrahedral sheet. Furthermore, the ESR spectra of the 8.4 Å hydrate showed a concurrent change in the line shape of the g = 4 signal from a shape usually associated with structural Fe in an ordered kaolinite, to a simpler one typically observed in more disordered kaolinite, halloysite, and montmorillonite. Either structural Fe centres and the O−-centres interact, or both are subject to factors previously associated with degree of order. The results question the long-term stability of the 8.4 Å hydrate, although XRD does not indicate interlayer collapse over this period. Complex inter-relationships are shown between intercalation, stored energy, structural Fe, and the degree of hydration which may be reflected in catalytic as well as spectroscopic properties of the clays.