Asulam (p-aminobenzenesulphonylmethylcarbamate) is adsorbed by alkaline and alkaline-earth cation saturated montmorillonites at room temperature either by protonation or by physical forces. On heating it decomposes to different products depending on the polarizing power of the exchange cation. On Mg–clay, sulphanilic and carbamic acid are obtained; the latter decomposes after equilibration at 100% relative humidity. In Ba– and Ca–systems, sulphanilamide and sulphanilic acid are produced with minor amounts of p–aminobenzenesulphonylcarbamate anion. Sulphanilamide is the main decomposition product in Na–, K–and Cs–systems. On Li–clay, decomposition of the Asulam results in the formation of p–aminobenzenesulphonylcarbamate anion and p–aminobenzenesulphonylcarbamic acid, probably as a consequence of the intermediate polarizing power of this cation.

The effects of dry grinding on the structure, morphology and properties of imogolite have been investigated by means of X-ray powder diffraction analysis, IR, DTA, and measurements of CEC and specific surface area. Imogolite is very susceptible to alteration by grinding compared to layer silicate minerals such as halloysite, kaolinite and montmorillonite. In the earlier stages of grinding, the parallel array of imogolite tubular structure units is markedly disturbed. On further grinding, disruption of Si-O-Al linkages, polymerization of the silica component released and loss of structural OH groups proceed simultaneously, these changes eventually resulting in complete breakdown of the structure. Ground imogolite is reaggregated finally into granular particles of irregular shape. All these changes are associated with a decrease in water holding capacity, CEC and specific surface area.

The processes taking place during decomposition of montmorillonite by percussive grinding have been studied by IR, X-ray and DTA methods. Destruction can be described as a series of parallel changes in the montmorillonite structure which proceed at various rates. The fastest is a change in status of the exchangeable cations followed by that of the hydroxyl groups. The slowest degradation process is the separation of tetrahedral and octahedral sheets. Degradation of the structure proceeds by delamination of particles, breaking of layers, crushing of layers by shocks perpendicular to the ab-direction, rearrangement of coordination polyhedra and transfer of protons within the structure. The relative importance of each of these processes is evaluated. It is assumed that the matrix resulting from complete breakdown of the montmorillonite structure consists mainly of the residue of tetrahedral sheets and deformed incomplete tetrahedra and octahedra, or of individual atoms held together in clumps either by Van der Waals forces or possibly, in some cases, by newly formed chemical bonds.

Los rasgos característicos geológicos (relieve bajo o medio, clima árido-semiárido, contrastado) y mineralógicos (asociación ópalo-alunita-caolinita) de niveles continentales Prelutecienses apoyan una hipótesis genética no hidrotermal. La evaporación de aguas portadoras de sílice disuelta, procedente de una meteorización del basamento, durante una estación seca, en depresiones, conduce a una precipitación de ópalo. Por otra parte, la desecación de áreas cubiertas por vegetaciones implica una descomposición bacteriana anaeróbica de materia orgánica y génesis de sulfuros; posteriormente, la aireación oxida a estos sulfuros y se generan aguas sulfatadas ácidas. Estas se mezclan con las que contienen silice, precipitando entonces conjuntamente ópalo, alunita y, si el Al3+ está en exceso, tambien caolinita.

A sepiolite from Toledo, Spain, was activated with dilute solutions of HNO3 (0·25, 0·50 and 0·75 m) followed by heat treatment at 110, 200, 300, 400 and 500°C for 10 h. The retention of n-butylamine in cyclohexane solution was used to follow the variation of surface acid centres of the sepiolite as a function of the acid and heat treatments, these reaching a maximum for the product treated with 0·75 m HNO3 and heated at 300°C. Acid treatments within the range 0·50–0·75 m and subsequent heat treatment at 200–300°C for 10 h yielded products with the highest surface activity.

Huit saponites de synthèse à charge croissante ont été étudiées à l'état ‘zéro couche’ (vide, P2O5) avec différents cations interfoliaires.

On observe—avec le cation K—une croissance linéaire du paramètre b en fonction du taux de substitution Si-Al, mais cette croissance est bien plus faible que celle observée avec les mêmes minéraux hydratés à ‘deux couches’.

On observe par ailleurs pour les cations K, Ba, Rb et Cs des relations linéaires entre les valeurs du paramètre b et de d001 d'une part et le rayon du cation d'autre part. Les cations plus petits (Na et Li) conduisent à des solutions structurales différentes. Avec le sodium la structure 1 M n'est plus conservée, les feuillets sont décalés les uns par rapport aux autres. Avec le lithium, le type d'empilement 1M est conservé mais c'est l'entité Li+-H2O qui est piégée dans les cavités ditrigonales placées face à face.

L'ensemble de ces résultats permet de montrer que les interactions entre touche interfoliaire et feuillets sont beaucoup plus fortes dans l'état ‘zéro couche’ que dans les états hydratés à une ou deux couches d'eau. Ces interactions sont fonction du rayon des cations interfolaires et peuvent entraîner une rotation des tétraèdres, ce qui conduit à discuter de la validité des équations donnant l'angle de rotation α en fonction de la composition des phyllosilicates.

Interstratified kaolinite-smectite minerals form the major part of a pedon transitional between ‘red’ kaolinitic and black smectitic soils in a soil toposequence derived from basalt in Burundi, Central Africa. These interstratified kaolinite-smectites have many X-ray, morphological and chemical features in common with ‘tabular halloysite’. Modifications to the 00l spacings of these minerals brought about by thermal and chemical treatments, however, show that they are not halloysite but consist of a mixture of ∼70% kaolinite and 30% smectite randomly interstratified. Field evidence indicates that these clays can be considered as a transient stage in the overall reaction smectite→kaolinite + iron oxides, which takes place in this landscape whenever the slope gradients give rise to better drainage conditions.

A swelling chlorite from unweathered basalt has been characterized by XRD, IR, DTA and chemical analysis. Its 001 spacing of 14.9 Å increases to 18.0 Å on treatment with glycerol and decreases to 13.9 Å (with a broad diffraction effect at 14-10Å) after heating to 550°C. The mineral has an 060 spacing of 1.537Å consistent with a trioctahedral composition, but its OH stretching band at 3638 cm−1 does not show the expected pleochroism, suggesting an anomalous hydroxide sheet which chemical analysis shows is incomplete. Although the mineral has a CEC of ∼50 mEq/100 g, smectite is not present, but all the techniques show that the mineral has some saponitic character, indicating that it probably has a structure intermediate between swelling chlorite and saponite.