Lower Palaeozoic shales and slates in the External Domain of the southern Canadian Appalachians are composed predominantly of illite and chlorite with minor occurrences of I-S mixed-layer minerals (restricted to samples with illite crystallinity, IC > 0·62°Δ2Θ) and paragonite (restricted to samples with IC < 0·42°Δ2Θ). Inverted diagenesis has occurred in the NW part of the Chaudière Nappe, indicating pre-orogenic deep burial diagenesis at the original depositional site, whereas to the SE, the diagenetic pattern was affected by synorogenic heating. Within the east-dipping thrust-fold belt and the St Lawrence Lowlands, increasing grade towards the S suggests a gradual southward increase in post-tectonic burial depth. Narrow (3–5 km) thermal haloes around the Cretaceous Monteregian intrusions show limited effects on the country rocks.

The percentage of 2M1 mica polytypes and bo increase with decreasing IC. Chlorite crystallinity (CC) increases with increasing IC. Good correlations between IC, %2M1, CC and bo of micas indicate that these parameters are reliable monitors of high-grade diagenesis and low-grade metamorphism in clay-rich sedimentary rocks. IC and CC improve with increasing grain size, illustrating the effect of grain size on IC and CC. Organic material affects IC more strongly in strata with lower permeability than in those with higher permeability. In the diagenetic zone, glycolation does not uniformly produce a narrowing of the 10 Å illite peak, but may also broaden it by up to 15%, probably due to the presence of Kalkberg-type mixed-layers.

A mild acid attack of the Llano vermiculite produces porous materials suitable for use as cracking catalysts and/or catalysts supports. After HCl attack at 80°C (1 m), the number of acid sites measured by the Hammett indicator method is ∼0·50/nm2, and the specific surfaces are 245 m2/g after calcination at 550°C (4 h), and 55 m2/g after steaming at 750°C (4 h). The performance of leached (1 m HCl) vermiculite has been compared with another hydrocarbon cracking catalyst—γ-Al2O3. The leached vermiculite produces a definite higher conversion and higher C3, C4 and gasoline yields, but much lower coke production. By electron microscopy, infrared spectroscopy, X-ray powder diffraction and thermal analysis, it has been shown that the leached vermiculite samples are composed of more or less attacked layers retaining their original platy morphology, and non-crystalline hydrated silica. Chemical analyses indicate that octahedral cations are dissolved first.

Desautelsite, a Mg(II)Mn(III) hydroxy carbonate first described in 1979 and represented by the general formula Mg(8−x)Mn(III)x(OH)16(CO3)x/2 (in which 2 < x < 2·67), has been synthesized under controlled pH conditions (induced hydrolysis) and coprecipitation techniques. In the pH-stat syntheses, the desautelsite is formed by aerial oxidation of MnCO3 in 0·05–0·15 m Mg(NO3)2 solutions at ∼pH 9 and temperatures of 35°C where, in the absence of Mg, manganite would normally form. The synthesis product from this technique is generally more crystalline than that formed by the coprecipitation method. Composition, particle shape and aggregation may be controlled through variations of the Mg concentration, pH, aeration rate or temperature. Indirect evidence suggests Mn to be present in the +3 oxidation state in the desautelsite.

Exchangeable cation associations in physical mixtures of bentonite and laponite have been examined using X-ray diffraction and a combination of electron microprobe analysis and multivariate statistical methods. The results suggest that cation exchange can occur in air-dry mixtures when pressure (∼64 kbar) is applied. Although no attempt is made to describe the mechanism of the reaction it appears to require the presence of adsorbed water.

The mineralogical and geochemical characteristics of the Tirschenreuth and Kohdachi kaolin deposits, which both occur in granite, are compared and the genesis of the deposits discussed. The Tirschenreuth deposit (Rappauf pit) is considered to have formed by weathering because: (i) the kaolinite has formed by the alteration of plagioclase and biotite, whereas microcline and muscovite are unaltered; (ii) the kaolin body has a very homogeneous composition and alteration zones cannot be recognized; (iii) there has been no addition of trace elements from sources other than plagioclase and biotite in the parent rock; (iv) particle-size distribution shows that the kaolinite crystals grew under uniform physical conditions; (v) quartz grains have smooth surfaces.

The Kohdachi deposit contains many clay veins and three alteration zones: (i) halloysite with weak silicification; (ii) halloysite-kaolinite; (iii) kaolinite. Many large dissolution pits were observed by SEM on the surface of quartz crystals from the kaolin zone. Silicification, precipitation of goethite at the border of zones (ii) and (iii), and dissolution of quartz in different areas of the deposit indicate a variable pH within a distance of <100 m. The Cu and Li contents in the <2 µm fractions of the Kohdachi kaolin samples are markedly higher than those at Tirschenreuth. From hydrogen isotopic analysis, the formation temperature of the Kohdachi kaolinite may be roughly estimated at 70–150°C. It is suggested that the Kohdachi deposit formed by hydrothermal alteration.

The EDTA-insoluble residues from five samples (two from the oolitic shoal facies and three from the lagoonal facies) of the Late Permian Ca-2 unit (Zechstein) have been investigated by X-ray diffraction, infrared spectroscopy, and scanning and transmission electron microscopy with energy dispersive X-ray analysis (EDXA). The results show that spheres of non-crystalline hydrous feldspathoids (with Al/Si molar ratio between 1·5 and 2·2) dominate the residues of samples from the oolitic shoal facies. Samples from the lagoonal facies are dominated by crystalline material (muscovite and quartz), but two of the samples contain a small number of spheres. Analyses of these samples by selective area diffraction and EDXA revealed the presence of small amounts of non-crystalline hydrous feldspathoids with Al/Si molar ratio between 0·1 and 1·9.

X-ray diffraction methods are effective and practical for the quantitative analysis of the often forgotten amorphous material phase in sediments. The method reported is simple, employing normal oriented samples, and quartz or fluorite as a diluent. However, special care must be taken to prepare the samples properly, to ensure optimum conditions for diffraction, and to measure accurately the scattering bands.

A smectite formed by weathering of mica in a laterite pallid zone at Boddington, Western Australia has been investigated by analytical electron microscopy. The evidence suggests that this mineral has the chemical composition and swelling properties of ideal beidellite but is anomalous in containing abundant non-exchangeable K. This K balances half of the layer charge that arises mostly from tetrahedral substitution of Al3+ for Si4+, with the K+ occupying one sixth of the sites occupied by K in mica.

De-intercalation of DMSO from well-crystallised kaolinites induced disorder. SEM, XRD and low-temperature IR were used to probe changes in morphology, layer stacking, and the environment of OH groups, respectively. The degree and type of disorder depended on the starting material and on the method of removing the intercalate. Rapid removal by heating at 250°C caused smaller changes than more prolonged heating at lower temperature, or washing with water.

A series of weathered Paleozoic slates was studied in an area southwest of the Montes de Toledo mountain range where the weathered slates are overlain by a raña formation and show three weathering levels. The fresh slate (at 30 m depth) is composed of ferrous chlorite, mica, quartz and feldspars. In the lowest part of the weathering profile the ferrous chlorite begins to evolve to smectite, and in the intermediate level, all the chlorite has been transformed into smectite. In the upper level (in contact with the raña formation), the smectites evolve to kaolinite, and the micas, which are unaffected at greater depths, begin to evolve to vermiculite, and there has been segregation of the free iron oxyhydroxides producing red, ochre and white zones. Two principal weathering processes, separated in time but superimposed, have been identified.

X-ray diffraction was used to analyse the distribution of clay minerals in the <2 µm fraction of the lutitic and marly facies from the centre of the Basque-Cantabrian Basin (Basque Arc), where the sedimentary section is 2000 to 10,000 m thick. Most of the deposits were laid down during the Cretaceous and Paleogene and were related to the opening and closing of the Bay of Biscay. The most noteworthy variations are in kaolinite, smectite and mixed-layered (R = 0, R = 1 and R ≥ 3) illite-smectite, which can be ascribed both to provenance and to diagenesis. A general diminution in expandability is related to the gradual transformation of smectite to illite from south to north, and with depth. Temperature, residence time and chemical activity during diagenesis are the factors that had greatest influence on the changes in the original mineral assemblages inherited from the source area. On the basis of the clay minerals and the Kübler index, a general scheme is proposed for the diagenetic evolution of the area from the initial stages to anchimetamorphism.

The spatial and vertical distributions of six clay mineral assemblages were identified in the pelagic marls and marly limestones and in the Ammonitico Rosso of the Lower Jurassic in the Betic Cordilleras (SE Spain). The six assemblages contain varying proportions of illite, kaolinite, chlorite, smectite and mixed-layer illite-smectite. The clay mineralogy and the geochemical data, particularly for the rare earth elements, indicate that the sediments were deposited in a pelagic environment influenced by a nearby continent. The source areas were many and lithologically varied. Clay mineralogy and geochemistry are shown to be most useful in the reconstruction of the palaeogeography of a basin in a passive continental margin.

The nature, crystallochemistry, organization and surface properties of soil clays derived from the most representative sedimentary formations of France are described, using qualitative and quantitative mineralogical methods and high resolution transmission microscopy (HRTEM). The main results show that soil clays differ significantly from reference clays. Even when 2:1 phyllosilicates are dominant, the clays always contain multimineral phases. The smectitic component is dioctahedral and of beidellite type. Soil clay organization is specific: all the clay particles have a short lateral extension and few layers (mean 5 layers, and even mono-layers occur). The superposition of such small particles leads to the formation of what are called “texturally interstratified minerals” which are dominant in soil clays. Exchange and surface properties (high ratio of external surface to total surface area), are related to clay organization.

Oedometer swelling and compaction tests up to a maximum pressure of 32 bars were made on the Wyoming montmorillonite SWy-1 with a range of mixed (Na,K) exchange ion compositions. The permeabilities and water diffusivities of the compacted clays were calculated using soil physics theory. Significant inhibition of swelling from that of the Na-montmorillonite is developed for K fractions in the range 0·30 < K+ < 0·56. However, the water diffusivity increases by a factor of approximately six as the K exchange fraction increases from 0 to 0·7. Permeabilities to water flow show a power-law dependence on the void ratio e.

XRD measurements at controlled humidity yield equilibrium interlayer spacings which in general increase with both increasing relative humidity and increasing Na exchange fraction. The extent of swelling is strongly inhibited in clays having Na exchange fractions of 0·44 or less, in good agreement with the oedometer studies.

Diagenetically modified muscovite grains occur as a frequent component of many Upper Palaeozoic and Mesozoic fluvial-deltaic sandstones and siltstones from Britain and the North Sea. Mineralogical, textural and chemical investigation of examples from the Great Limestone Cyclothem show that such grains consist simply of muscovite and kaolinite. No other sheet-silicate phases are involved. Diagenetic textures indicate that modified grains result from the displacive growth of kaolinite between opened cleavage sheets of detrital muscovite. Fabrics of this type should consequently be termed kaolinite-cemented. In contrast to similar sheet-silicate intergrowths reported from diagenetically altered biotite and chlorite, little or no alteration of muscovite is actually required to account for observed textures.

Grain-size distribution, specific surface, thermal analysis, electron microscopy and X-ray diffraction were used to study the effect of dry grinding on the structure and properties of two kaolins of different degree of crystallinity. Grinding caused particles to fragment and resulted in the formation of stable large spheroidal aggregates of fine particles. These two processes were not clearly separated by a specific grinding time, but occurred in parallel shortly after grinding was started, although aggregate formation persisted at longer grinding times. The variation in the specific surface area during grinding was found to be dependent on these two processes and on the particle size and crystallinity of the initial kaolin. DTA and XRD data and the amount of water released at different temperatures revealed grinding to gradually destroy the kaolinite structure and cause the loss of hydroxyl ions and the formation of others that were subsequently removed at low and medium temperatures. An explanation for the process whereby the new hydroxyl ions are formed is provided.

The adsorption of aminotriazole, at its solution pH, with montmorillonite saturated with different cations has been studied. A pesticide-montmorillonite complex is formed through interlamellar cations which are not displaced. Aminotriazole is situated mostly as a polarized molecule around Mg2+ and Zn2+ cations, removing a great amount of water. In Na+- and Li+-montmorillonite, the pesticide remains as a non-polarized molecule, hydration water being retained in the interlamellar space; the pesticide is coordinated to interlamellar cations through water bridges. For all samples a proportion of cationic aminotriazole is also adsorbed, the amount being greater with increasing polarizing power of the interlamellar cation; consequently, in Fe3+-montmorillonite all the aminotriazole adsorbed is in the cationic form.

Upper Jurassic claystones of Kimmeridgian-Volgian(-Ryazanian) age are the main source rocks for oil in the Central Trough, North Sea. Drill cuttings and cores from the depth interval 2368–4548 m, the interval from early-mature to peak oil generation, have been investigated by high-resolution transmission electron microscopy (HRTEM) of ion-milled rock samples, and by HRTEM and powder X-ray diffraction (XRD) of dispersed illite-smectite (I-S) mixed-layers isolated from the <0·2 µm fraction. Ordering parameters were determined by XRD profile simulation. TEM on shadowed particles, combined with XRD evidence, showed that dispersed I-S consists of a mixture of 10–70 Å thick particles, whereas HRTEM showed that intact bulk rock was dominated by 50–200 Å thick particles. Disruption, possibly along smectite planes, of the larger particles in the bulk rock formed the thin particles in dispersed I-S. HRTEM showed 20 and 30 Å periodic enhancement in the contrast of lattice fringes in bulk rock samples as well as in dispersed I-S crystals. These features were interpreted as ordered I-S crystals. Indications of disintegration of larger I-S particles during sample dispersion and of the presence of ordered I-S crystals in the intact bulk rock support the layer transformation mechanism for the conversion of smectite to illite.