Interpretation of K-Ar determinations of the apparent age of crystallization of diagenetic potassic layer silicates should take into account the current ideas concerning the smectite to illite conversion of clay minerals. These minerals are the major K-bearing neogenic phases in sedimentary rocks and, therefore, it is important to keep in mind their origin and the pathway of their evolution. Another important contributor to K and Ar content are detrital minerals which are not considered in detail in this paper. The radiogenic Ar retained by diagenetic illitic clay minerals (illite and illite-smectite interstratified minerals with a low smectite content) will be a function of: (1) the amount Ar lost through the destruction of mixed-layer and small grained illitic material dissolved to produce new, larger, illite-rich crystals; and (2) the amount of Ar produced and retained in the growing, stable illite mineral grains. Hence the K/Ar ratios in diagenetic illites depend on several variables. In samples where the detrital contribution is small, when the illite growth reaction is rapid, i. e. occurring over a short period of time, the accumulated radiogenic Ar can be used to date the geologic event which caused this crystal growth. However, if the process occurs over a significant period of time, as is usually the case in shales, the age deduced by radiogenic Ar content will indicate the changes in mineralogy and grain-sizes of the different participating phases. These changes will be the result of time and temperature variables of the sedimentation and burial of the samples studied. The radiogenic Ar accumulated will reflect a sequence of mineral changes over a period of time.

Sequences of alternating arenaceous and argillaceous lithologies are commonplace in the siliciclastic hydrocarbon reservoirs of the North Sea and elsewhere. Individual lithological units may vary in thickness from millimetres to tens or hundreds of metres. The first part of this introduction will discuss general aspects important for the understanding of the patterns of clay diagenesis associated with these sequences, whereas the second part will deal with the papers presented in this issue of Clay Minerals and how they fit into this general area of interest.

Absorption lines in the g ∼ 4 region of ESR spectra of three New Zealand halloysites were found to originate from similar paramagnetic centres as in kaolinites. Resonances in the g ∼ 4 region were not common to all the halloysites, although the signal at g = 2·0 for the Matauri Bay halloysite is probably due to a trapped positive hole or trapped ion. A 6-line resonance produced by Te Puke halloysite and removable by Na-saturation is attributed to exchangeable Mn on the clay surface. Low-temperature lines exhibited by all samples are due to V4+ or VO2+ replacing Al3+ in the octahedral sheet.

Interpretation of downhole wireline logs is generally a major source of information used to build up a picture of the quality and distribution of reservoir rocks. Logging tools respond to a number of variables and comparison of a suite of different logs is usually required to isolate and identify the response due to a single factor, e.g. porosity or clay content. A new tool, the litho-density tool (LDT), has been used along with conventional logging tools in a mid-Jurassic sand/shale sequence. The LDT simultaneously measures Pe (effective photoelectric cross-section) and ρa (apparent bulk density). Pe is a function of atomic number which in turn reflects lithology or mineral composition. By using cross-plots derived from the LDT and other logs, patterns of mineral abundance are indicated.

Clay minerals occur as replacements of olivine, pyroxenes, plagioclase and interstitial materials, and as vesicle fillings, in altered basalts from the Middle Atlas (Morocco). Phyllosilicates are the main components of this alteration process. They have been characterized here by optical microscopy, X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy as saponite, talc, corrensite and chlorite. The homogeneity of the chemical compositions of these phyllosilicates, in different alteration environments, probably means that they are controlled by the composition of the hydrothermal fluid. Talc-saponite-corrensite (with dominant saponite) is the clay mineral association most frequently observed (corrensite being more abundant in the vesicular levels of the basalts). Such an association, with no evidence of albite and zeolite, suggests that these basalts have suffered minimal alteration at relatively low temperatures. Another association, chlorite-corrensite, was detected in a deeper (vesicular) sample, probably resulting from a slightly higher temperature. Lastly, only discrete phyllosilicates (i.e. no random mixed-layer minerals) were observed. This suggests that near-equilibrium conditions prevailed during this alteration stage and that a dissolution-crystallization process was the main mechanism of transformation.

Sudoite occurs as a cryptocrystalline clay in some Visean K-bentonites from Belgium. Usually associated with illite-smectite mixed-layers, this chlorite has been found locally as a monomineralic clay component of a K-bentonite bed. The mineral has a composition close to (Al3Mg2)(Si3Al)O10(OH)8. The cell parameters have been calculated from the diffractogram using the space group C2/m (a = 5·228, b = 9·056, c = 14·326 Å, β = 97°00′, d(060) = 1·509 Å). The polytype corresponds to a IIb structure. Some hypotheses are proposed for the origin of this chlorite. The coexistence of sudoite and pyrite could explain why the chlorite present in Visean K-bentonites is not a Fe-rich species typical of diagenetic conditions, but a Fe-poor one.

Le dosage de l'opale biogène dans les sédiments marins peut être effectué par diffractométrie X par la mesure des surfaces des bandes de diffusion et par la mesure des surfaces des pics de cristobalite. La surface de la bande de diffusion, observée sur les diagrammes X de sédiments non chauffés, caractérise la concentration en composés amorphes (organiques et inorganiques). Elle permet de quantifier l'opale biogène de sédiments ne contenant que peu ou pas d'amorphes non biogènes. La surface du pic de cristobalite, obtenu par transformation de l'opale biogène par chauffage à 1050–1100°C pendant 12 h, permet de doser la silice biogène de divers sédiments. Ces deux approches méthodologiques ont été appliquées aux sédiments d'une carotte (MD 84–527) prélevée dans le secteur ouest-Indien de l'Océan Austral. Ce matériel, qui a enregistré la sédimentation des 40,000 dernières années, ne renferme qu'accessoirement des constituants amorphes volcaniques. Les concentrations en silice biogène sont obtenues avec une précision de ±10%. Le comptage des diatomées par observation au microscope a été également réalisé sur les mêmes sédiments. Les courbes des teneurs en opale biogène obtenues par les deux méthodes sont comparables et se corrèlent bien à l'abondance totale des diatomées.

Careful (00l) fourier syntheses have been made on muscovite, pyrophyllite, and montmorillonite (dehydrated), in an effort to discover the cause of the different (00l) spacings of these minerals. The oxygens of the outer (tetrahedral) layer superpose exactly in these syntheses, those of the inner (octahedral) layer almost exactly. Thus the differences are entirely in the inter-layer spaces, and are probably due to electrostatic repulsion of the negatively charged multiple layers. As the negative charge increases (and with it the repulsion, and hence the inter-layer spacing), in the series pyrophyllite-montmorillonite-mica, the net energy of binding of the sheets increases also. The two variations are not in contradiction.

It follows from this work that the shifts in cell size due to ionic substitutions are entirely taken up in the plane of the layer, its thickness remaining the same.

Examination of field samples shows that the alteration of the bentonite beds of Wyoming and Montana near the surface to produce high-quality, highswelling, commercial bentonites is analogous to pedocal soil development. The near surface bentonite has undergone extensive calcification, and in some zones it is so heavily altered as to diminish its swelling properties. These low-swelling bentonites can be activated by conventional soda-ash additions. The naturally high-swelling materials have undergone only partial calcification and do not require soda-ash modification. The relatively unaltered 'grey' or 'blue' bentonites have undergone little or no calcification. The latter have the highest Na to Ca ratios, are non-swelling, and do not respond markedly to soda-ash additions. Such low-swelling materials will respond to calcium-activation with markedly improved physical quality parameters of flocculation as measured by Marsh Funnel and Fann viscosimeter. The study indicates that vast reserves of low-swelling bentonites in Montana-Wyoming may be susceptible to controlled calcium activation and expanded commercial utilization.

The comparison between measured and predicted smectite percent (%Sm) in an illite-smectite (I-S) mixed-layer series was used to estimate the thermal conditions of diagenesis in the Ardèche sedimentary series. Measurements were performed using the decomposition procedure (Lanson & Besson, 1992) of XRD patterns obtained from oriented preparations (<0.2 μm fractions). Three particle populations were identified: I-S, poorly crystallized illite (PCI), and well crystallized illite (WCI); the %Sm was measured in the I-S population by comparison with calculated XRD patterns using the NEWMOD software (Reynolds, 1985). The theoretical evolution of %Sm with depth obtained with the two first-order kinetic reaction processes described by Velde & Vasseur (1992) was compared to the measured one at Balazuc. The best fit was obtained for the following conditions: 35°C km–1 and between 1500 and 2000 m for the thermal gradient and the eroded piles, respectively. The predicted values for I-S compositions in the 10–0% Sm range are overestimated by the model because the reaction controlling the composition is no longer the dissolution of I-S but the ripening of illitic particles (PCI and WCI).

Two zones can be distinguished in the sedimentary series: (1) down to 55 m, the %Sm of I-S particles is highly variable and seems to be controlled by local variations in permeability and chemical composition; (2) down to 550 m, the %Sm of I-S particles is more strictly dependent on the general time-temperature conditions. An anomalously high %Sm value is located in the vicinity of faults at 1669 m due to local change of the water/rock ratio.

The potassium pools of five major physiographic units of the Urmia region situated in western Azerbaijan province, north-west Iran, were studied to determine the distribution of K forms as functions of clay mineralogy and physiographic units. Soil samples from horizons of ten pedons were selected and analysed for physiochemical properties, clay mineralogy and forms of K. X-ray diffraction patterns revealed that the soils were similar in clay-mineral compositions, consisting of illite, smectite, chlorite, and kaolinite, for the different physiographic units, but vary in the relative amounts of these minerals. The illite content was highest in piedmont plain (P.P) followed by plateau (Pl), river alluvial plain (R.A.P), colluvial alluvial plain (C.A.R) and lowland (L.L) units. Smectite content was highest in Pl followed by P.P, L.L, R.A.P and C.A.P units. Several processes, such as the diversity of weathering rate, biocyclying processes of K accumulation, geomorphologic conditions and soil formation processes, caused significant differences in most K forms in the soils. A wide variation in total K (HF-extractable K) (0.54–1.1%), non-exchangeable K (280–450 mg kg–1) and exchangeable K (217–330 mg kg–1) occurred among the physiographic units, corresponding to variations in their mineralogical compositions, mainly the abundance of illite. Significant differences (P ⩽ 0.05) were found for K, HNO3-extractable K and non-exchangeable K between the soils with large illite contents (30–50%) and with small illite contents (10–30%). A significant positive relationship existed between mineral K and illite content (r2 = 0.85, P ⩽ 0.001) and non-exchangeable K and illite content (r2 = 0.84, P ⩽ 0.001). The results indicated that these pools of K are mainly released from the frayed edges and wedge zones of illite.

The soils developed from crystalline and metamorphic rocks in Galicia (NW Spain), are characterized by high concentrations of 1 : 1 phyllosilicates and gels. Thermal analyses, X-ray diffraction after formamide treatment, and IR spectroscopy in the OH vibration range have been performed on the clay fractions, but do not discriminate clearly between the different associated mineralogical phases. HRTEM studies linked with microdiffraction and microanalyses have led to the identification of several types of gel which transform into goethite, gibbsite, clay precursors, and/ or halloysite according to their composition (Fe, Al or Si-Al). Halloysite-like minerals are the main constituents and they have a great variety of morphologies: lamellar, spheroidal, tubular, platy or poikilitic. In general, halloysite and gel formation on crystalline rocks is related to the bioclimatic conditions, involving high hydrolysis in the presence of organic matter. This halloysite seems to be a metastable mineral which would evolve into kaolinite with increasing weathering time.

Hofmann & Klemen ont observé qu'en chauffant modérément (200-220°C) une smectite dioctaèdrique à substitutions octaàdriques saturée par du lithium, celle-ci perdait sa capacité d'échange cationique et son pouvoir de solvatation. Les auteurs ont attribué cet effet à la migration des cations Li vers la couche octaèdrique. Nous avons, en utilisant essentiellement la diffraction X aux grands angles et la microscopie électronique, caractérisé de manière quantitative la structure d'une smectite à déficit de charge mixte (c'est-à.-dire ayant 30% de substitutions dans les couches téraèdriques et 70% dans les couches octaèdriques) saturée par du nickel, avant et après chauffage. Nous avons ainsi pu montrer en éudiant les réflexions 00l qu'après un chauffage à 400°C, les cations interfoliaires migrent vers la cavité octaèdrique vacante pour compenser la totalité des charges négatives dues aux substitutions Al → Mg et qu'il existe une distribution inhomogène de la charge entre les couches octaèdriques et tétraèdriques au sein d'un même cristal. Certains feuillets ont des substitutions uniquement dans la couche octaèdrique, d'autres uniquement dans la couche tétraèdrique, et toutes les possibilités peuvent exister entre ces deux pôles extrèmes.

Thermoplastic polyurethane (TPU) matrix was reinforced with polyhedral oligomeric silsesquioxane (POSS) and halloysite nanotubes (HNT), both separately and combined. Composite samples were fabricated using a melt-compounding method. Characterization of the composites obtained was performed via tensile and hardness tests, melt-flow index measurements (MFI), abrasion tests, dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM) to investigate the mechanical performance, flow behaviour, tribological characteristics, thermo-mechanical response and morphological properties. The greatest tensile strength value was obtained for the smallest HNT content. Further addition of HNT resulted in agglomerations for both POSS and HNT particles. The shore hardness of TPU was enhanced by filler inclusions. The TPU/POSS composites displayed significant improvement in terms of abrasion resistance compared to TPU at lower loading levels. The DMA study showed that composites containing 0.5% POSS and 1.0% HNT displayed the greatest storage modulus. The glass-transition temperature of TPU shifted to smaller values with the addition of both nanoparticles. The HNT inclusions increased the MFI value of TPU because of their large aspect ratio. Homogeneous mixing of nanoparticles in the TPU matrix was confirmed by a SEM study of the composites. Their dispersion decreased as the concentrations of POSS and HNT increased. An adjuvant effect of POSS with HNT was achieved in their hybrid composites.

An iron catalyst supported on the modified Tamazert kaolin has been prepared and tested in catalytic wet peroxide oxidation using phenol and 4-chlorophenol (4-CP) as target compounds (100 mg/L initial concentration). Kaolin is not usually employed as a catalytic support due to its low developed porous structure, but its textural properties may be improved upon calcination and acid and basic treatment. The catalyst was characterized by N2 adsorption–desorption and chemical analysis by total-reflection X-ray fluorescence spectroscopy. The catalytic tests were carried out in a batch reactor with a stoichiometric amount of H2O2. The catalytic efficiency was studied within the temperature range of 25–55°C at an initial pH of 3.3 and 1 g/L catalyst. Complete phenol and 4-CP removal was achieved with no significant differences in phenol and 4-CP conversions within the temperature range tested. Meanwhile, total organic carbon (TOC) reduction was greatly favoured by increasing the temperature, which may be partially attributed to a probable contribution of a homogeneous reaction associated with iron leaching. However, this effect might be of limited significance because the highest concentrations of iron in the liquid phase were below 4.5 and 8.5 mg/L in the experiments with phenol and 4-CP, respectively. At 55°C, TOC was reduced by ~70% after 4 h reaction time, with the remaining by-products corresponding almost completely to low-molecular-weight carboxylic acids of very low ecotoxicity.

The present study focused on the assessment and possible applications of the clay from the Miličinica deposit, western Serbia. X-ray diffraction (XRD), Infrared (IR) spectroscopy, Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), Differential Thermal Analysis and Thermogravimetry (DTA-TG) and High Temperature Microscopy (HTM) were used to characterize the clay in question. The physical properties determined were colour, plasticity, specific surface area, particle-size distribution and cation exchange capacity (CEC). Clay minerals are the main phases in the samples studied, with illite being the predominant phase and kaolinite being present in variable amounts. Quartz, feldspars, carbonates and iron-bearing minerals were also detected. Varied technological behaviours were expected because of the mineralogy (illite and iron contents), average grain size (0.6–0.7 µm), specific surface area (≈60 m2/g) and plasticity index (≈13%). The classification of the clays studied, based on the main characteristics and using appropriate diagrams, suggests that they are easily adaptable for ceramic processes.

The FEBEX experiment, a full-scale, high-level radioactive waste repository test, ran for ~18 years and hence is the longest-running disposal test to date. The test consisted of a heater emplaced in an envelope of compacted bentonite at the Grimsel test site, Switzerland. The water content of the bentonite was somewhat lower near the heater and increased towards the granite. This phenomenon probably led to gradients in the exchangeable cation population at various locations within the bentonite buffer. The cement (shotcrete) bentonite interface of one block was characterized by a thin (0.1–1.0 mm) reaction zone in which bentonite constituents, carbonates and sulfates occurred. Cation exchange and a slight decrease of the cation exchange capacity were observed near the heater. Oxic corrosion was observed predominantly at the bentonite/steel liner interfaces, pointing towards a role of air entrapped between the liner and heater during emplacement. At the liner surface, intimate intergrowth of bentonite constituents, metal and corrosion products was observed. At the face of the heater, the bentonite blocks were in direct contact with the heater surface without any signs of metal corrosion. Instead, a significant increase in the Mg content was recorded, which is in agreement with previous large-scale disposal tests. The FEBEX experiment proved that the Mg increase and corrosion were independent processes. The increase in Mg may be explained by the formation of trioctahedral domains or the precipitation of neoformed silicates. For the first time, however, brucite was identified as an additional phase that formed at the metal/bentonite interface, pointing towards a special role for Mg mobility in the bentonite barrier.

Organo-kenyaites were prepared from a cetyltrimethylammonium hydroxide (C16TMAOH) solution and solid sodium kenyaite (Na2Si22O45.10H2O) mixture. The effect of the initial cetyltrimethylammonium solution on the structure of the intercalated materials was investigated by CHN analyses, X-ray diffraction (XRD), thermogravimetric analysis, SEM, and 29Si and 13C solid NMR techniques. For C16TMAOH concentration 0.25 mM, the Na+ cations were fully exchanged. Initial C16TMAOH concentrations higher than 0.25 mM had little effect on the intercalated amount of C16TMA+ cations. The organic cations content reached a plateau of 0.66 mmol/g. The arrangement model of C16TMA+ cations corresponded to a tilt of the organic cations to the silicate layers with an angle of 42° as deduced by XRD studies. The C16TMA+ cations exhibited mainly trans-configuration of the methyl chains, as was shown by solid 13C NMR. The thermal stability of the organo-silicates was studied using in situ FTIR and in situ XRD in the range 25–450°C. The C16TMA-kenyaites were stable at temperatures below 200°C. They collapsed at higher temperatures due to the decomposition of the intercalated surfactants. These organo-kenyaites were used to remove the acidic dye molecule, eosin. The removal tests were performed at varying conditions of initial dye concentrations, organic content in the organo-kenyaites and heating temperatures. In general, the organic modification improved the removal capacity of the Na-kenyaite from 2 mg of eosin/g to 60 mg of eosin/g, and this capacity was related to the organic contents and the calcination temperatures of the organo-kenyaites.

On étudie les équilibres de distribution de deux éléments de transition divalents A,B, entre gels silicatés inorganiques de formule SiO2-(A,B)O-nH2O et solutions aqueuses A2+,B2+ (A.B = Mg, Mn, Ni, Co, Cu, Zn). On montre que l'enthalpie libre molaire standard d'échange de deux éléments A,B entre gel et solution est une fonction linéaire de l'enthalpie libre d'échange calculée en considérant un échange théorique entre hydroxyde et solution. Les relations obtenues permettent de prévoir le comportement d'autres éléments divalents.

The fractal dimension values of several kaolins with different structural order and properties have been calculated from N2-adsorption isotherm data according to the Neimark method. All kaolins show a fractal regime in the same nitrogen relative pressure range, with fractal dimension values ranging between 2.38 and 2.57.

The correlation between fractal dimension and other kaolin characteristics (structural order of kaolinite, BET surface area, brightness and particle-size distribution) was determined. The correlation matrix shows that the fractal dimension (Ds) is highly correlated with the degree of structural order-disorder and is also moderately correlated with the particle-size distribution and brightness. No correlation was observed between BET and Ds, probably because the first is a measurement of the accessible surface while Ds represents the scaling properties of the area.

As Ds is a parameter easily calculated and related to the degree of surface heterogeneity, and well correlated with other kaolinite parameters, it can be used to estimate a set of kaolin technical properties for suitability of the kaolin in the paper industry.