In the Maláiguide Complex (Betic Cordilleras, Spain), dickite is widely developed in clastic Permo-Triassic sequences. The lateral extent stretches at least 300 km along the Betic range, whilst vertical extent is variable and appears limited to the lowest 20–150 m of these sequences. Textural, chemical and crystallochemical characteristics of the dickite, illite/mica and chlorite in dickite-bearing rocks and in the overlying (Permo-Triassic) and underlying (Carboniferous) rocks have been investigated to determine the approximate conditions in which dickite has developed. Using the chlorite geothermometer (based on A1IV contents), temperatures of 146±28°C and 169±12°C have been deduced for two Permo-Triassic members, and 305±12°C for Carboniferous. The Si content in illites has been used as a geobarometer, and pressures of 4.8±2 kbar have been estimated in Carboniferous rocks and tentative pressures of 2.7±3 and 2.1±2 kbar in Permo-Triassic members. Chemical evolution of phyllosilicates is accompanied by increasing illite crystallinity and % 2M1 polytype.

Pore-lining chlorite is common in Rotliegend lake shoreline aeolian sandstones from northern Germany and preserves abnormally high primary intergranular porosity. In the north of the study area, in a basinward direction, the chlorites are Mg-rich while towards the south they become Fe-rich over a distance of about 15 km. All are unusually rich in Mn. Magnesium-rich examples tend to be more abundant than illite, while Fe-rich examples cover framework grains less continuously and are admixed with more abundant illite. Oxygen isotope analysis of 30 chlorites in the 2–6 µm fraction gave δ18O (SMOW) values of 7 to 12‰ (mean 9.8‰). These data show no obvious trend across the study area, nor in relation to changes in chlorite composition, or burial depth.

The honeycomb arrangement of chlorite crystals suggests chlorite formation via the sequence smectite-corrensite-chlorite. Chlorite distribution and the systematic changes in its composition suggest that formation of a precursor was related to lateral migration of Mg-rich fluids from basinal shales and/or evaporites during shallow burial. Interaction of these fluids with early formed oxyhydroxide coatings on the aeolian sand grains provided a source of Fe and the Mn. The isotope data suggest that the eventual formation of chlorite during deep burial occurred from waters with positive δ18O values, comparable to those present during the deep burial formation of illite.

Fine-grained sediments are a major parent material in Ebro Valley soils. During the 1960s, the area was transformed by irrigation and soils underwent serious degradation processes. The sediments have a fine texture, high CaCO3 contents and high salinity-sodicity levels, and contain illite as the most important phyllosilicate in the fine fractions. Two groups of finely laminated organization have been recognized in terms of layer thickness and grain-size distribution. Based on texture, the microstructure of the silty and clayey layers is different, irrespective of their mode of formation; porosity characteristics also differ between layers, leading exclusively to a capillary evaporation flow that results in salinization of the plough horizons. The sediments are formed by two different mechanisms, each layer resulting from uninterrupted sedimentation of a suspension or from deposition of suspended particles by water discharge.

Palygorskite and associated clay minerals have been studied in a Pleistocene calcrete complex from the Negev desert (Sde Boqer, Israel). This complex is divided into five main parts: the chalky and marly bedrock overlain by its weathered product, a brecciated calcrete hardpan; the laminar crust; loess pockets trapped in the calcrete; and the overlying soft surficial soil. The distribution of clay minerals is directly dependent on the position of the sample in the calcrete complex. Smectite is inherited from the bedrock in the calcrete with an aeolian enrichment in loess pockets and upper soft soil. The source of kaolinite is mainly detrital, related to desert dust. Illite is partly inherited and partly neoformed in loess pockets and desert surficial soil. The origin of palygorskite is clearly related to precipitation processes from soil solutions, Si and Al ions being provided by the slope and detrital grains trapped in the calcrete, with Mg being provided by the parent rock, the slope and aeolian detrital dolomite. This neoformation occurs mainly around detrital grains such as quartz in the hardpan and along textural transitions in loess pockets and is associated with gypsum in the lower part of the toposequence where the evaporation fluxes are the most important. The existence as coatings around grains and the delicate structure of the fibres are incompatible with a detrital origin. Moreover, no evidence was found to support any transformation of smectite into palygorskite in the solid state. Palygorskite is the last step of the cycle of mobile silica and seems to be a product of late diagenesis in Sde Boqer calcrete.

A highly illitic phase containing <5–10% interstratified smectite was described by Mossmann et al. (1992) and, more recently, by Clauer et al. (1995) from Upper Triassic sandstones of the Paris Basin (France). This phase is present in all size-fractions of all samples and was interpreted as authigenic. The K/Ar model ages of this illite range from 189–200 Ma and, combined with oxygen isotope data, were cited as evidence of high-temperature (220–250°C hydrothermal precipitation from highly 18O-enriched fluids at burial depths of only 500 m.

We suggest that this type of illite is more likely to be diagenetically altered detrital illitic material and unlike authigenic illite-smectite which is also present in many of their samples. This reassessment of their petrographic observations leads to a much more realistic diagenetic interpretation consistent with previous studies of the basin and avoids the need to invoke basin-wide hydrothermal activity during shallow burial.

Spötl et al. (1996) have re-examined studies published by us on clay materials of sandstones in the Paris Basin. They refute the XRD characterization, K-Ar dating and formation temperature of one of the interstratified illite-smectite phases identified and have provided an alternative explanation of the published results. However, the authors ignored some basic data provided in the publications under discussion, and they have not been able to explain readily why some of the data were discarded. Furthermore, part of their disagreement is unsubstantiated. We maintain that, on the basis of coherency and consistency of all the data obtained, as well as on independent published results, the most satisfactory interpretation for the thermal evolution of the Paris Basin is the one that we suggested in our publications.

A quantification technique useful in analysis of clay-rich deposits containing sepiolite and/or palygorskite has been developed by combining diffractometric and chemical data and represents a considerable improvement on classic quantification based on X-ray diffraction. The required data are: intensity ratios between certain diffraction peaks of calcite-dolomite and sepiolite-palygorskite-smectites, and also the CaO, MgO, K2O, Al2O3 and SiO2 contents. The validity of this method was tested by analysis of artificial mixtures of pure phases of the minerals found in such deposits.

The chemical and structural stability of a Spanish sepiolite from Vallecas, Spain, was studied in 0.04 n NaOH (pH = 12.6), a saturated solution of Ca(OH)2 (pH = 12.6) and deionized/distilled water (pH = 7). The chemical stability was evaluated by determining the concentrations of Mg, Si and Ca in the solid residues during the kinetic test. The structural stability was studied by determining the changes in specific surface area and ‘crystallite’ size. The specific surface was determined by the BET method and the ‘crystallite’ size by the profile of the X-ray diffraction line. The main conclusion was that sepiolite is a material with high chemical stability in neutral and alkaline media, with no significant structural changes. However, in alkaline media, greater dissolution of silica was observed than in neutral media, the silica being derived from the most external tetrahedra attached to the OH− groups.

A series of reduced-charge montmorillonites (RCMs) was prepared from Li-montmorillonite from Jelšový Potok (Slovakia) by heating at various temperatures (105–210°C for 24 h. The amount of fixed Li, 0.09–0.67 per O20(OH)4, increased with increasing temperature, confirming preparation of a set of samples of variable layer charge from the same parent Li-montmorillonite by varying only the preparation temperature. Infrared spectroscopy revealed that Li was trapped in the hexagonal cavities of the tetrahedral sheet at all temperatures. Partial deprotonation of the samples, reflected in the decrease of the intensities of the OH-bending bands, was observed after treatments above 120°C. Analysis of the OH-stretching region showed Li in the previously vacant octahedra in the samples heated above 150°C. Weak inflections near 660 and 720 cm−1 confirmed development of local trioctahedral character of octahedral cations coordinated with OH groups in the sample heated at 210°C. Gradual decrease of the layer charge due to Li fixation led to a shift of the Si-O stretching band to higher frequencies and to the appearance of new, pyrophyllite-like bands at 1120 and 419 cm−1.

One-dimensional swelling tests and hydraulic conductivity tests have been performed at vertical effective stresses up to 450 kPa on Na-bentonite powder and compacted sand/Na-bentonite mixtures (5, 10 and 20% bentonite by weight) to investigate the use of bentonite-improved soils for waste containment. It was found that bentonite powder swells to reach a final state described by a single straight line on a plot of void ratio against the logarithm of vertical effective stress, regardless of preparation technique. Swelling of sand/bentonite mixtures expressed in terms of the clay void ratio show a deviation from bentonite behaviour above a stress which depends on the bentonite content. Hydraulic conductivity data for bentonite and sand/bentonite mixtures indicate an approximately linear relationship between logarithm of hydraulic conductivity and logarithm of void ratio. A design model based on the clay void ratio, and the sand porosity and tortuosity is presented enabling the hydraulic conductivity of a mixture to be estimated.

Kaolin has been used as an alternative cheap raw material for the synthesis of zeolite 4A. Two steps are involved in the reaction: (1) dehydroxylation of kaolin at 550–900°C to form an activated X-ray amorphous material called metakaolin; (2) hydrothermal treatment of metakaolin with aqueous alkali to form the zeolite. The inherent colouring impurities in kaolin, especially the Fe minerals, affect the brightness of metakaolin and the resultant zeolite. The dehydroxylation temperature is found to have a significant influence on the kinetics of zeolite formation as well as on the brightness of zeolite. The present investigation deals with the preparation of metakaolins from a good quality kaolin at different temperatures and their characterization by XRD, IR, TGA, MAS NMR and brightness measurements. Hydrothermal reactions of these metakaolins with aqueous alkali have been conducted. The residual Fe in the mother liquor has been estimated. The improvement in brightness and change in reactivity of the metakaolin, difference in the kinetics of its conversion to zeolites and dissolution of Fe during zeolite formation have been correlated with the calcination temperature. A calcination temperature of 900°C (1 hr) is the optimum for this clay to change into a reactive metakaolin which gives detergent grade zeolite 4A of high crystallinity and maximum brightness.

Thermoporometry (TPM) was applied to hydrotalcite precipitates prepared with carbonate, bicarboxylic acids and chloride. It was used to measure the formation of an ice body between the hydrotalcite particles. Before TPM could be applied, the dried hydrotalcite precipitate had to be soaked for two weeks in water. The mean value of a factor F measured by TPM, which described the shape of the ice body in hydrotalcite, was 1.7. This value was between those of a purely cylindrical (F = 2) and a purely spherical ice body (F = 1), indicating the formation of ice lenses. From the radius of the ice body, Rn, ice volume, Vn and shape factor F, the corresponding specific surface area of the hydrotalcite particles could be assessed. The TPM indicated that the distance between the separate hydrotalcite crystals in water, which is equal to 2(Rn+0.9) nm, was a function of the type of anion incorporated at the interlayer, such as chloride and bicarboxylic acid. The pore volume and surface area of the hydrotalcite particles measured by TPM were compared with those determined by the traditional nitrogen sorption technique on dried hydrotalcite. It appeared that sorption of N2 yielded much lower values than TPM. This difference was interpreted as being due to slow penetration of N2 through the dried hydrotalcite samples to the interparticle voids.

La diffusion aux petits angles des rayons X (DPAX) a été utilisée pour caractériser l'évolution de la structure et de la texture d'argiles fortement hydratées en fonction de la température (Pons, 1980; Pons et al., 1981), de la concentration en sel (Saez et al., 1983) ou en fonction de la pression (Tessier, 1984; Ben Rhaiem et al., 1986, 1987). La méthode permet d'accéder aux paramètres structuraux du système par comparaison des courbes expérimentales à des courbes théoriques calculées à partir de modèles.