The adsorption and desorption of water, the layer spacing of the montmorillonite with increasing water content and the heat of immersion with water have been measured for a Na-bentonite and two Ca-bentonites. The bentonite-water system is treated in terms of a micropore-filling process. Uptake of water occurs in discrete stages as the montmorillonite structure expands and the internal surface is calculated from these discrete stages of water adsorption.

L'altération de biotites et de muscovites en halloysite a été mise en évidence par l'étude en MEB dans l'altération de roches granitiques et de micaschistes. Cette transformation débute par le développement d'un réseau losangique à la surface des feuillets de micas. La croissance par épitaxie de tubes d'halloysite est parfois accompagnée par celle de cristaux de goethite. Le MEB montre que l'halloysite se forme directement à partir du mica et qu'elle apparaît dans les tous premiers stades de l'altération, quelles que soient les conditions.

The interaction of chrysotile and crocidolite with water has been investigated in an attempt to identify the factors affecting the rate and the degree of dissolution of asbestos fibres within groundwater systems at landfill sites. Dissolution experiments were used to investigate rate laws and to obtain apparent activation energies for the dissolution of the two minerals. The activation energies related to transport-controlled processes, but as the overall dissolution occurred so slowly it was unlikely to be controlled by processes with such low activation energies. Congruent dissolution of both minerals tended to increase with temperature and time, suggesting that in the long-term environmental situation, congruent dissolution of these two asbestos minerals would occur. However these experiments show that, as the reaction was so slow, there is little likelihood of reduction of the asbestos pollution hazard by the complete dissolution of fibres on prolonged contact with natural waters.

Thermal transformations of kaolinite were studied by 29Si- and 27Al-MAS/NMR and ESR techniques. In metakaolin, Si is still dominantly in the Q3 state (three Si atoms bonded to an Si-O4 tetrahedron) and Al detectable by NMR is in both 4-coordination and 6-coordination. Coordination polyhedra around Al or Fe replacing Al are much distorted. Metakaolin crystallizes into γ-alumina and mullite exothermically at ∼980°C, this crystallization being preceded by a faint endothermic reaction. The latter is due to segregation of SiO2 and Al2O3, which results in an increase of Si in the Q4 state and an increase of 6-coordinated Al2O3.

The filtration of suspensions containing clay and other particles in water is a common process in drinking water treatment. Such filtration processes are very efficient, producing clear water containing less than 1 mg/l from suspensions with particle concentrations of up to 100 mg/l. This filtration is not straining, but a process of collection of clay particles on the sand surfaces in the pores. The clays may range in size from sub-micron to ∼20 µm, and may be flocculated, and are retained in pores ∼200 µm in size within sand grains ∼500 µm in diameter. The collection process has three principal components (i) transport of clay particles across laminar water streamlines by diffusion, gravity and hydrodynamic forces, (ii) attachment by electrical or van der Waals' forces with hydrodynamic forces intervening, (iii) detachment by fluid shear or instabilities caused by arriving particles. Mathematical and physical models relate suspension concentration, quantity of deposit and permeability to depth in a filter, and time of operation. Fibre-optic endoscopes with CCTV enable video recordings to be made of the behaviour of clay particles in the filter pores, at magnifications up to 500 ×.

Mineralogical and chemical examination of Tertiary interbasaltic clays from the Faeroe Islands revealed three types of alteration of volcanic tufts and basalts: (1) Argillization of volcanic tuffs within a lacustrine environment resulted in the formation of aluminous beidellites and metahalloysites; these clays are associated with extensive coal layers at Suduroy. (2) Argillization of volcanic tuffs due to hydrothermal action resulted in the formation of thick layers of ferriferous beidellites associated with small amounts of hematite and zeolite (e.g. at Nolsoy). (3) Meteoric alteration of volcanic tufts and basalts, which took place under hot climatic conditions and contrasting seasons, led to the development of ferriferous and aluminous-ferriferous beidellites, metahalloysite, kaolinite, hematite and goethite in low (Høv profile) or high (Øravik profile) topographical positions. The three processes occurred individually or were superimposed.

Aluminium-substituted goethites were synthesised in 0·3 M KOH at either 25° or 70°C. The 25°C goethites had unit-cell a and c dimensions about 0·1–0·2% larger than the 70°C goethites of comparable Al substitution. Unit-cell b dimensions were similar regardless of synthesis temperature. The 25°C goethites contained larger amounts of Al in their structures than the 70°C goethites synthesised at the same initial Al/(Al + Fe) mole ratio in solution. The 25°C goethites had lower dehydroxylation temperatures and smaller differences between the two OH-bending bands than comparable 70°C goethites. These differences between the two sets of goethites are believed to be caused by the presence of more structural defects in the 25°C goethites than in the 70°C goethites. Goethites with the lowest Al substitutions consisted of crystals with several coherently diffracting domains, while at high Al substitutions the crystals were mainly monodomainic. Surface areas of the 25°C goethites varied in a complex manner as a function of thickness along [100], character of the domains, and physical size.

A method of analysing the colloidal stability of variable-charge mineral suspensions as a function of pH is described, which combines light scattering with soluble element and surface charge measurements. The absorbance of the suspensions closely follows the A = k−m equation, where m = −dlgA/dlgλ is an aggregate light-scattering index which is inversely related to the limiting sedimentation speed v = dA600nm/dt. Usually, suspensions of variable-charge minerals scatter less near their point of zero charge where the aggregation process is a maximum, in contrast to environments where they are charged and well-dispersed. Although the morphology of goethite is that of elongated needles, kaolinite plates, and imogolite tubes, the coalesced sphere approach of the Mie theory allows rapid correlation of the absorbance at 600 nm with aggregate-size distribution, indirectly measured by the light- scattering aggregate-size index m confirmed by electron microscopy experiments. Kaolinite and goethite suspensions obey the diffraction scattering law with a variation in size of 2–20 µm from the dispersed to the aggregated particles. Imogolite and alumina gel suspensions possibly obey the anomalous diffraction scattering law and are present as 0·05–1 µm aggregates of their 50–100 Å structural units. Silica gel and the more dispersed imogolite suspensions possibly obey the anomalous Rayleigh scattering law with a variation of aggregate size from 700–3000 Å.

Mixed-layer clay minerals of illite-smectite, having smectite contents ∼25% and IS ordering, kaolinite-smectite, and a three-component variety with kaolinite-smectite-chlorite-like material are described from a Carboniferous paleosol in South Wales. The clays, which are restricted to particular horizons, are unusual occurrences in a pedogenic sediment and pose particular problems as to their genesis. Positive geological evidence, principally in the form of mineralogical and organic thermal maturation data, demonstrates that the rocks of the region cannot have reached diagenetic temperatures > 100°C. This would appear to suggest a pedogenic rather than a diagenetic origin for these clays. In these sediments the only plausible mechanism of illitization to produce the illite-smectite would be by repeated wetting and drying cycles causing irreversible K fixation. Such cycles would be entirely realistic for a vertisol-like paleosol formed on overbank deposits in a floodplain environment subject to strong seasonal moisture contrasts. If this interpretation is correct, this illite-smectite represents the most illitic yet recorded from a non-burial or non-hydrothermal environment.