The occurrence of metahalloysite ‘nodules’ in the silica sand pocket deposits near Brassington, Derbyshire, is recorded for the first time. The geological surroundings are briefly described in an attempt to arrive at an explanation of the genesis of the ‘nodules.’ The history of attempts to work the deposits as china clay in the 18th century is included.

A general expression for diffracted intensities from partially ordered layer structures with a ‘mistake’ has been calculated. The ‘mistake’ consists of a shift of a layer parallel to adjacent layers by any arbitrary fraction b/q along the b axis, q being any integer. The expression is free from any simplifying approximations.

The interaction between interlamellar Lu(III) cations and the layered silicate structure has been studied by means of MAS-NMR, XRD and EDX. Irreversible fixation of exchangeable Lu(III) cations upon hydrothermal treatment at 300°C of Lu-saturated montmorillonite is reported, through the formation of the crystalline phase Lu2Si2O7. It is shown that the lowest temperature previously described for this reaction, 400°C, does not indicate a thermodynamic boundary. This basic solid-state finding is relevant for some clay applications such as those related to the safety of nuclear waste repositories with engineering barriers.

Solutions obtained from soils in the Galicia Region of NW Spain had considerably lower activities of Al3+ when obtained by a speciation procedure (fractionation with an ionic column and application of specific software) than when obtained from concentrations of reactive Al (colorimetry with pyrocatechol violet) by a calculation that only considers simple hydroxylated species. Using the speciation method, many of the solutions obtained from surface horizons are unsaturated for most minerals, especially in granitic areas.

This study focuses on the main factors determining the apparent porosity of porous bioceramics prepared using small organic foam spheres as the pore-making reagent, in order to determine the best technical parameters for preparing porous bioceramics. In every experiment, only one of these factors (the time of heating, the sintering temperature, the mass ratio between small organic foam spheres and beta-tricalcium phosphate (β-TCP) powder, and the rate of the temperature rise) was changed, while the others were kept constant. In each case the apparent porosity was tested and the relation between the specific variable and apparent porosity was observed. Finally, the optimum technical parameters were deduced. The apparent porosity shows an inverse linear relation to the time of heating and the sintering temperature, and is approximately proportional to the mass ratio between the small organic foam spheres and the β-TCP powder and the rate of temperature rise. These factors have important influences on the apparent porosity. The optimum conditions were: heating time (soak time) 120 min, sintering temperature 850ºC, mass ratio 0.25, and a rate of temperature increase of 120ºC h–1.

Complexes formed between 0·034 m dimethyltin dichloride solutions and Na-montmorillonite at pH 2·4 and 4·0 have been characterized using 119Sn Mössbauer spectroscopy, X-ray diffraction, infrared spectroscopy, thermogravimetric analysis and water sorption isotherms. The dominant exchange cation at pH 2·4 is Me2Sn2+ characterized by an isomer shift, δ, and quadrupole splitting, Δ values of 1·25 and 3·80 mm s−1, respectively. The major exchange cation at pH 4·0 is the dimer, [Me2SnOH]22+, (δ = 1·38, Δ = 3·34 mm s−1) although the monomer, Me2Sn(OH)+, (δ = 0·95, Δ = 3·29 mm s−1) is also present. These complexes have basal spacings of 15·0 and 16·0 Å, respectively, which are stable up to 200°C. Mössbauer spectroscopy has shown that these ions are converted to SnO2 via Me2SnO upon thermal degradation. The temperature at which these oxides appear coincides with the collapse of the basal spacing. Both complexes display BET Type IV isotherms for the adsorption of water, following thermal pretreatment at 150°C, but the complex prepared at pH 4·0 has a lower sorption capacity. Both complexes, contrary to the normal behaviour of layer-silicates, have a definite pore volume and no further uptake occurs when this is filled.

On étudie l'influence des cations compensateurs sur le spectre P.I.R. d'une vermiculite hydratée à deux couches. La définition d'un paramètre IR permet de quantifier cet effet. On conclue que l'énergie d'hydratation du cation est en relation avec la rigidité de la couche interfoliaire.

In electric fields, anisodiametric mineral particles in suspension orientate and align. When tagged with fluorescent molecules, the alignment is accompanied by changes in the intensities of the polarized components of the emitted fluorescence. By measuring these changes under specific experimental conditions, any non-random directional coincidence of the absorption and emission transition moments associated with the dye molecules can be evaluated and the spatial array of the dyes estimated. From such measurements, the binding of the optical brightening agent FBA1, a triazinylaminostilbene compound, to sepiolite has been studied.

Talc [ideal formula: Mg3Si4O10(OH)2] is one of the classical 2:1 trioctahedral phyllosilicates that has been analysed intensively with respect to its formation, thermal stability, chemical properties and structure (e.g. Wilkins & Ito, 1967; Rayner &Brown, 1973; Ward, 1975; Martin et al., 1996). Single crystal structure refinement by X-ray diffraction (XRD) showed clearly that talc is triclinic and crystallizes in the space group CI (e.g. Rayner & Brown, 1973; Perdikatsis & Burzlaff, 1981). Based on this structural model, two coordination arrangements of OH groups to Mg in the octahedral sheets can be deduced. Since XRD data give only an insight into the average structure, local information on the ligand field of the cations is limited. Currently, no analytical tool is known to determine directly the ligand field of Mg in the octahedral sites.

No comprehensive study has yet been conducted to determine the chronostratigraphic distribution of palygorskite in the Tertiary sediments of Iran. Thirty sediment samples of different Tertiary epochs were taken, based on the field observations and geological maps. The clay fraction of samples was then investigated by X-ray diffraction (XRD), transmission and scanning electron microscopy (TEM and SEM), and inductively coupled plasma mass spectrometry (ICP-MS). Results showed that sediments of the Miocene and Pliocene had large amounts of palygorskite whereas no trace of this mineral was found in the sediments from the Palaeocene, Eocene and Oligocene. Geochemical analyses revealed that sediments younger than the Oligocene had greater amounts of soluble Mg and H4SiO4 and a higher pH than those of the Palaeocene and Eocene. The stability diagram of the smectite-palygorskite system suggests that smectite is unstable and transforms to palygorskite in Neogene sediments. The SEM micrographs showed palygorskite as interwoven fibrous mats, coatings, pore-fillings and pore-bridging material in Neogene sediments. This textural evidence suggests a direct chemical precipitation of palygorskite by dissolution of silicates under the alkaline conditions. The results also suggest that geochemical conditions in the Early Tertiary era, represented by deep-sea conditions in central Iran, were not apparently favourable for palygoskite formation until the Late Oligocene.

Se realiza un estudio detallado de las distintas fases minerales (caolínicas y silíceas) que aparecen en rocas silicificadas tanto graniticas como sedimentarias de la provincia de Avila.

Las técnicas utilizadas (A.T.D., difracción de rayos X, microscopía electrónica de trasmisión y de barrido) permiten establecer una clasificación de estos minerales segun sus propiedades térmicas, parámetros cristaloquímicos, y morfologías identificadas al scaning.

Sa dá una interpretación genética a cada uno de los tipos de caolinitas encontrados (macrocaolinitas en acordeón, microcaolinitas en gusanillo y criptocaolinitas). Los dos primeros tipos pueden ser explicados por procesos conjuntos de alteración hidrotermal y ‘weathering’ de feldespatos y micas. El tercer tipo (criptocaolinitas) es de más difícil interpretación al aso-ciarse con ópalo C-T en diques que cortan a rocas granitoideas y otras veces al presentarse como matriz de areniscas sedimentarias.

The Numidian Aquitano-Burdigalian nappe from the Jijel region (northeast Algeria) shows an important clay-rich basal series. In this study, seven representative clay samples were collected from the Djimla and El-Milia areas of this region in order to analyse their mineralogy using X-ray diffraction and Fourier-transform infrared spectroscopy, chemical composition by X-ray fluorescence, particle size, plasticity, morphology by scanning electron microscopy and their ceramic properties. Samples were prepared by pressing the clays and firing them at 800–1100°C, and bulk density, water absorption, linear firing shrinkage, weight loss and bending strength values were determined on the fired samples. The clays are mainly composed of kaolinite and illite, with a small amount of 10–14 Å interstratified clay minerals and chlorite, associated with quartz and feldspars. The main oxides in the samples were SiO2, Al2O3 and Fe2O3. The clays may be classified as moderately plastic according to their Atterberg limits. Ceramic tiles have been produced by dry pressing. At all tested firing temperatures, the clays present the required standard values for linear firing shrinkage, weight loss, bulk density, water absorption and bending strength, and they are defect-free. The main transformations were observed at 1000°C with the appearance of new crystalline phases. The measured technological properties of the investigated deposits confirm that the Numidian clays from the Djimla and El-Milia regions are suitable materials for the production of high-quality structural ceramics.