This work examines a tuff from the Tinebdar deposit located in Sidi Aich (east Algeria) for possible use as an alternative material for the adsorption of Asucryl red (a textile dye). Natural tuff represents an economic and environmentally friendly alternative compared to synthetic zeolites. The starting materials were characterized by means of powder X-ray diffraction, Brunauer–Emmett–Teller-specific surface area and pore diameter analysis. Batch experiments were performed and various parameters that have an effect on the adsorption process (i.e. pH, clay amount, contact time and initial concentration) were investigated. The <125 μm grain-size fraction of the tuff contains 45 wt.% mordenite. The adsorption equilibrium was established in 10 min and the adsorption kinetics were better described by the second-order kinetic model. The adsorption isotherm of the results obtained fits better to the Langmuir and Timkin models. The adsorption capacity qt varies from 60 to 70 mg g–1 with temperature increasing from 293 to 333 K. The thermodynamic nature of the adsorption process was determined by calculating ΔH°, ΔS° and ΔG° values. The positive value for ΔH° confirms that the adsorption is endothermic.

Some parameters of the firing of kaolin around 900°C are examined: (1) firing shrinkage; (2) densification, hardening and textural evolution of kaolin ceramics. Experimental results are accounted for by an empirical formula describing the isotherm firing shrinkage of kaolin ceramics.

Depending on the precursor salt added, the spreading and dispersion of the mineralizer is more or less homogeneous. If, during thermal decomposition, the salt induces much porosity, this effect can counterbalance the shrinkage caused by the mineralizer. The kinetics of shrinkage, and the final density after firing depend both on the latter effects and on the mineralizer cation. A very good correlation is observed between shrinkage, final density (residual pore volume) and the strength of the fired clay product. The introduction of uniformly dispersed mineralizers causes an increase in mechanical resistance (for identical temperatures and firing times) by a factor greater than 3, occasionally 5) and, for equal firing times and mechanical strengths, lowers the firing temperature by 100-200°C.

Sorption interlayer complexes of n-butylamine, sec-butylamine, iso-butylamine and diethylamine with homoionic Ln-montmorillonites (Ln = La, Sm, Gd, Er, Y) have been prepared. Compositions of the complexes are of the type: [Ln(butylamine)4]3+ and [Ln-(diethylamine)2]3+. The disposition of amine molecules surrounding the ion, the interaction between the amine group and the Ln3+ ion, and the strength of the ion-dipole bond have been studied by X-ray diffraction, IR spectroscopy and differential thermal analysis.

Mixed-layer minerals with optical properties similar to metamorphic vermiculite were identified in rocks belonging to a Palaeozoic and a Triassic formation separated by an angular unconformity and exposed in the Coastal Range of central Chile. Both formations are affected by low-grade metamorphism. The mixed-layer minerals were studied by optical microscopy, X-ray diffraction (XRD), electron microprobe (EMPA), and transmission/ analytical electron microscopy (TEM/AEM). Two types of phyllosilicates were identified: chlorite-vermiculite and mica-chlorite, which are present in the Palaeozoic and Triassic rocks respectively. Chlorite-vermiculite mixed layers form packets with well-defined boundaries and mainly show 1:1 ordered sequences. On the contrary, mica-chlorite mixed layers show, in most cases, random sequences evolving laterally toward chlorite. The AEM data indicate compositions close to that of chlorite in the ternary Si-Al- (Fe+Mg+Mn) diagrams for both types of mixed-layer phyllosilicates. Relative to the coexisting chlorite, they have lower (Fe+Mg) contents, and a higher Si/Al ratio. They are interpreted as products of the transformation of chlorite, developed during prograde metamorphism, and probably represent intermediate, metastable phases, in the chlorite to biotite transformation.

Zwitterionic porphyrin (tetrakis {4-(2-carboxyethyl)pyridinio}porphyrin (TPyCP)) with four pyridinium and carboxyl groups in the molecule was synthesized. The adsorption behaviour of TPyCP on the montmorillonite clay surface was examined in an aqueous colloidal solution. While the adsorption maximum λmax of TPyCP was 424 nm in water, it shifted to longer wavelengths on complex formation with clay. The λmax on the exfoliated clay surface was 450 nm, and that in the stacked clay sheets was 471 nm, respectively. Under alkaline conditions ([NaOH] = 2 × 10–4 M), the stacking behaviour of the clay was completely suppressed. It emerged that anionic parts in the porphyrin molecule can suppress the stacking of clay sheets. Judging from the quantitative analysis, the maximum adsorption amount of TPyCP was 100% vs. cation exchange capacity (CEC) of the clay. As the adsorption density of TPyCP increased, λmax shifted slightly to longer wavelengths due to the interactions between adjacent porphyrins. When the loading level of TPyCP was 200% vs. CEC, the stacking of TPyCP was indicated. The average stacking layer number was calculated to be 1.48. On the other hand, it is known that tetra cationic porphyrins without anionic parts do not form such stacking structures. Thus, it seems that zwitterionic porphyrin has the potential to form a three dimensional structure through electrostatic interactions between porphyrins on the clay surface.

Chlorite (C)-corrensite (Co)-smectite (S) seriesminerals occur as vein constituents in the two epithermal ore veins, the Chuetsu and Shuetsu veins of the Todoroki Au-Ag deposit. The characteristics of the C–Co–S seriesminerals indicate that the clays may be products of direct precipitation from hydrothermal fluids and subsequent mineralogical transformations during and/or after vein formation. The minerals from the Chuetsu vein are characterized by ‘monomineralic’ corrensite showing an extensive distribution throughout the vein, and trioctahedral smectite occurring locally. The Shuetsu vein minerals are characterized by C-Co series minerals which can be divided into three different types: a I type including discrete chlorite with minor amounts of S layers, a II type comprising interstratified C/Co and discrete chlorite, and a III type characterized by segregation structures of C and Co layers. The C-Co series minerals show slightly different spatial distributions in the Shuetsu vein. Different epithermal environments during the vein formations and possible kinetic effects may have played a role in the formation and conversion of Co-C series at the Shuetsu vein and S-Co series at the Chuetsu vein.

This paper describes a detailed petrographic and isotopic study of hypabyssal sheets of quartz-syenite that represent the ultimate differentiation product of the oceanite alkaline magmatic reservoir of the Piton des Neiges stratovolcano (Réunion Island). Clay minerals of the corrensite to chlorite series crystallized during the late-magmatic activity, with quartz, carbonates and accessory minerals from juvenile fluids filling the primary porosity of the quartz-syenite. It is proposed that a double chemical transfer occurred at the end of the crystallization process: degassing of the exsolved CO2-rich and SiO2-rich fluid from the magmatic chamber through the porous quartz-syenite and diffusion of Al, Fe and Mg from the intruded basalts affected by the juvenile fluids towards the primary porosity of the quartz-syenite, feeding the crystallization of late-magmatic clays in the residual primary pores after quartz and carbonate deposition. This process may be generalized to alkaline plutonism, as well as to the primitive crusts of terrestrial planets, and may be the first source of clays in early planets.

This review demonstrates that high-resolution transmission electron microscopy (HRTEM) imaging of clay minerals or phyllosilicates with an incident electron beam along the major zone axes parallel to the constituting layers, in which the contrast corresponds to individual cation columns in the images obtained, is indispensable for elucidating the enigmatic structures of these minerals. Several kinds of variables for layer stacking, including polytypes, stacking disorder and the interstratification of various kinds of unit layers or interlayer materials, are common in phyllosilicates. Local and rigorous determination of such variables is possible only with HRTEM, although examination as to whether the results obtained by the HRTEM images from limited areas represent the whole specimen should be made using other techniques, such as X-ray diffraction. Analysis of these stacking features in clay minerals provides valuable insights into their origin and/or formation processes. Recent state-of-the-art techniques in electron microscopy, including incoherent imaging, superior resolutions of ~0.1 nm and low-dose imaging using new recording media, will also contribute significantly to our understanding of the true structures of clay minerals.

Le mécanisme de rètention de l'octylbenzènesulfonate de sodium (OBSNa) en milieu aqueux pur sur les argiles correspond essentiellement à une précipitation du sel de calcium (OBS)2Ca. L'adsorption, proprement dite, atteint à peine 2 à 3 µEq/g d'argile. En présence de KCl, la part de l'adsorption devient plus importante à cause de l'augmentation de la solubilité du sulfonate de calcium. L'affinité des monomères du tensio-actif pour l'interface solide-liquide est accrue. On montre que l'adsorption varie avec les propriétés de l'argile, en particulier, avec le nombre et la nature de ses cations échangeables. L'équilibre d'adsorption dépend de l'état d'avancement des réactions d'échange entre les cations échangcables de l'argile, les cations apportés par l'électrolyte (KCl) et le monomère (Na+), et les cations adsorbés sur les micelles. II existe, pour chaque argile, une concentration limite en KCl, d'autant plus grande que la teneur en calcium de l'argile est élevée, et à partir de laquelle le tensio-actif ne précipite plus. La rétention se fait alors uniquement par adsorption. Suivant les conditions de pH, elle a lieu sur les cations échangeables de l'argile et les sites positifs à la périphérie des cristaux (kaolinite) ou seulement sur les cations échangeables (illite et chlorite). Dans les procédés de récupération assistée du pétrole, l'addition de chlorure de potassium au fluide de balayage permettra de réduire la précipitation du tensio actif. Même, si l'adsorption augmente, cet effet est souvent suffisant pour que, globalement, la rétention diminue.

The climatic history of the Dead Sea region during the Pliocene and its global connection are observed from climate-sensitive rocks and clay minerals of the Sedom formation. The Sedom formation consists of evaporative halitic rock salt units and calcareous shale units that were deposited in the Dead Sea Basin during the Pliocene. The precipitation of the rock salts took place in the hypersaline sabkha environment of the Sedom Lagoon. The extensive evaporative conditions are related to an extremely dry and warm arid climate at that time. In the arid climate, the influx of meteoric water by the drainage system of the Sedom Lagoon was limited and permitted a large concentration of lagoonal brine as well as a small rate of detritus transportation to the lagoon. Accessory sepiolite found in the rock salt appears to be neoformed from brine enriched with Mg and poor in Al under the extreme salinity condition. The small amounts of Al are in accordance with the small number of detrital minerals in the rock salts. The replacement in the deposition of the rock salt members with the calcareous shale members demonstrates a decrease in the salinity of the brine in the Sedom Basin and an increase in the deposition of detritus. The change in conditions was related to a period of deposition under a more humid climate where the erosion and the transport of detritus by the drainage system to the Sedom Basin was higher, causing the deposition of calcareous shales. Palygorskite found in the calcareous shales appears to be neoformed from brine enriched with Mg and containing Al in conditions of reduced salinity of the Sedom Basin. The larger amounts of Al are in accordance with the abundance of detrital minerals in the calcareous shales.

The depositional cycles of the Sedom formation, the cyclic fluctuation of the climatic-hydrologic conditions from an arid to a more humid climate and their correlation with sea-level fluctuations and transgression-regression cycles of the Mediterranean Sea seem to be a response to corresponding global interglacial and glacial periods during the Pliocene.

Electron microscopic examination of montmorillonite from the deposit near Redhill shows that the particles of the so-called blue clay are predominantly lathshaped with an average length: width ratio of 5. The so-called yellow clay from Redhill also contains a high proportion of similar lath-shaped particles, but many smaller lamellar particles are present which appear to be the results of lateral fracture of the laths. The majority of particles of montmorillonite in the fullers' earth deposit near Bath, Somerset, are platy with a similar shape distribution to Wyoming Bentonite, although smaller in size.

The electron microscopic technique used is based on a positively charged supporting film which, immersed in a clay suspension, preferentially selects negatively charged montmorillonite from the predominantly uncharged impurities. A conventional replica technique also showed lath-shaped particles in the blue clay.

The possible practical consequences of the different particle shapes are discussed.

A simple jig is described for the construction of a model of the muscovite structure in which the distorted hexagonal, i.e., ditrigonal, arrangement of the basal oxygens of the tetrahedra is accurately represented. The model is of the packing kind as opposed to the ball-and-spoke kind and demonstrates the advantages of this type of model, which would be more generally used if transparent plastic balls were available commercially.

Any X-ray diffraction (XRD) pattern of mixed-layered maximum R1 ordered chlorite-smectite has an exact equivalent R0 smectite-corrensite or R0 chlorite-corrensite. The identification of a mineral as chlorite (0.8)-smectite R1 is, therefore, not evidence that the fundamental layers in such an interstratified structure are actually chlorite and smectite. Furthermore, there are no obvious differences between XRD patterns of R0 and R1 chlorite-smectite at high or low smectite contents. Therefore the frequently supposed identification of R0 chlorite-smectite with high smectite contents is also questionable. It follows that the identification of R1 chlorite (0.8)-smectite by Robinson & Bevins (1994) and of R0 chlorite (≈0.2)-smectite in an earlier publication (Robinson et al.,1993) cannot be used as evidence regarding the debate over the nature of the component layers in interstratified minerals intermediate between trioctahedral smectite and chlorite.

Diffraction patterns of natural mixed-layer chlorite minerals from metabasites often show a strong reflection at 31 Å yet a lack of resolution of other mixed-layer peaks from those of discrete chlorite. These features cannot be matched by any single mixed-layer mineral consisting of layers of chlorite and smectite and were matched by Robinson & Bevins (1994) using a mixture of different chlorite-smectite minerals. However, they can be matched by a single chlorite-corrensite mineral in which there is an element of segregation of layer types. These different possibilities need to be investigated further.

Dickite occurs over wide areas along the Italian Apennines strip throughout Italy, mainly in the allochtonous ‘varicoloured’ clay-shale formation. Morphological, fabric and crystallochemical features suggest an authigenic origin, from pore solutions. The nature of the solutions and the process of dickite formation, including hydrothermalism, diagenesis or supergene evolution have all been discussed. Stable isotope analysis (O, H) was performed to investigate these points. The δD values of dickite range between −63.7 and −79.1% (SMOW) and δ18O between +21% and +16.1‰ (SMOW), and are similar to those reported for kaolinites formed in equilibrium with meteoric waters. The data fall along the ‘Line of Meteoric Kaolinites’, supporting an origin involving meteoric waters and low temperatures. The isotopic compositions of the waters are within the range of Apennines meteoric water, and the temperatures derived are close to surface conditions. Contributions of diagenetic, hydrothermal or metamorphic waters must be discounted. The authigenic dickite from ‘varicoloured’ clays of the Italian Apennines formed by precipitation from flushing meteoric waters whose ingress was favoured by repeated surface erosion.

Weathered soil material derived from tectonically emplaced serpentinized ultrabasic intrusive rocks of southern Cameroon has received considerable attention from mining companies due to its extractable-metal (i.e. Ni, Co) potential. As these cations can be incorporated into Fe oxides, it was deemed appropriate to study the mineralogical assemblage of a highly weathered serpentinite soil profile from the area. This study focuses on the different Fe-oxide phases, which were investigated using 57Fe Mössbauer spectroscopy, showing goethite and hematite as the dominant Fe oxides throughout the weathering profile. These minerals, in association with gibbsite and kaolinite, indicate an advanced degree of weathering. The clay fraction of the ‘Lower Limonite’ layer, above the saprolite and at a depth of 7 m, is very rich in goethite, whereas hematite and magnetite are almost absent. Above this layer, the hematite content in the fine-earth and clay fractions increases upwards, while the goethite content remains constant. The significant substitution and change in the particle size of the goethite and the poor crystallinity of hematite, as indicated by the hyperfine parameters and XRD, suggest that the upper material evolved under different pedological conditions compared to the deeper layers. The mixed composition of the upper layers (above 7 m), which contain muscovite and a relatively chaotic distribution of trace elements, suggests ancient mica-schist capping and possibly different cycles of erosion and pedimentation.

During solventless alkylation of phenol with 4-hydroxy-2-butanone under microwave irradiation, paratoluenesulfonic acid (pTSA)-modified montmorillonite clays gave, regioselectively, 4-(4′-hydroxyphenyl)-2-butanone (raspberry ketone). The duration for this reaction under microwave irradiation is much shorter than that of the conventional method. A comparative study of the alkylation reaction over a montmorillonite clay sample treated with 0.5 M-pTSA (0.5 M-pTSA clay) with that of Al-exchanged montmorillonite (Al3+-Mont) and beta-zeolite (HB) was carried out. The results show that the reaction time to reach equilibrium and the product distribution pattern for the reaction over 0.5 M-pTSA clay were similar to those values for the HB. Micropores formed on the clay surface during the pTSA treatment were found to enhance the rate of formation of C-alkylation. Micropores appear to enable better access to the active sites during the course of reaction.

The recent discovery of a Roman ceramics manufacturing workshop at Montelabate (Perugia, Italy), in use from the first century BC until the late-fourth to fifth centuries AD, offers a unique opportunity to study the technical processes for producing Roman amphorae. Ancient and modern clays were sampled and analysed; they do not differ significantly, supporting the hypothesis of the exploitation of the rich local clay source that allowed a continuity of production. Characterization of the clays was performed using geotechnical methods (Atterberg limits and size distribution) and by thermogravimetric and differential thermogravimetric analysis, Fourier-transform infrared spectroscopy, X-ray diffraction and X-ray fluorescence analyses. The material was suitable for pottery making with the addition of calcite and quartz sand temper. Production waste and discarded materials as well as good-quality products were also analysed with the same methodology. It is therefore possible to reconstruct the ancient technology by defining the recipe for the production of the amphorae and their firing temperature on the basis of the decomposition of clay materials and the presence of newly formed minerals.

Scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) analysis of smear slides of oriented <2 mm clay fractions is shown to be a reliable and rapid analytical technique for providing chemical data on clay mineral mixtures. Such smear slides are routinely prepared for clay mineral analysis by X-ray diffraction and the only additional treatment required for chemical analysis by EDS is carbon-coating to form an electronically conductive surface. Using standard clays, mixtures of standard clays, and sediment samples, it is shown that sample thickness, sample heterogeneity and surface roughness do not introduce significant analytical errors, although the presence of non-clay mineral phases such as calcite, dolomite, quartz and pyrite may introduce minor discrepancies. Chemical data complement the XRD analyses and increase their accuracy and reliability.