Polycondensation reactions between amino acids and phenols are one of the pathways for the formation of humic substances, and clay minerals are able to catalyse these reactions. To investigate the catalytic power of allophane, an allophane fraction (ALF) was separated from weathered pumice (WP) that contained imogolite as an impurity by taking advantage of differences in sedimentation velocity. The iron content in the separated ALF was increased by up to 3.0% compared to that in the starting WP (1.3%), and the ALF was further treated with sodium dithionate and citric acid (ALF-DC) to remove the iron. The catalytic powers of WP, ALF and ALF-DC were evaluated, based on the degree of darkening of reaction mixtures from polycondensation reactions between catechol and tryptophan, model compounds for precursors of humic substances. The catalytic power for ALF was significantly higher than the corresponding values for WP and ALF-DC. This can be attributed to the high iron content of the ALF, which serves as a Lewis acid that can enhance nucleophilic reactions which occur during the polycondensation reactions.

Examination of rock samples from Job's Hill, St Mary, Jamaica, by chemical, X-ray, differential thermal, and infrared analyses showed predominant dickite with associated nacrite and kaolinite. The uniqueness of this deposit makes it possible that selected material could be used as a standard mineral.

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.

Seven samples from a chronosequence of soils developed in historically created polders on the Atlantic coast (Marais Poitevin, Vendée, France) were investigated in order to illustrate the rate of mineralogical change in a clay-dominated system. The oldest polder was constructed in 1665, the last one in 1912; thus the time span of soil evolution is from 80 to 330 years. All the samples had more than 50% clay (<2 μm). The most reactive, fine clay sub-fraction (<0.1 μm) was investigated in detail by X-ray diffraction and chemical analysis. The observed mineralogical changes with increasing age followed the schematic reaction:

smectite + mica = illite + mixed-layer minerals.

The progress of reaction in time appears to be non-linear. This reaction seems to occur in a chemically constant system, and the mineralogical change can be seen as a readjustment of species to a given chemical composition.

The extent of diagenesis in Lower Jurassic shoreline sandstones of the Beatrice oilfield was controlled primarily by their detrital clay content. Sandstones rich in detrital clay had low depositional permeabilities; these show preservation of detrital feldspars to the present day and have no extensive diagenetic quartz overgrowths. Sandstones poor in detrital clay had high permeabilities and show large quartz overgrowths as part of a normal sub-arkosic diagenetic sequence. Such quartz occurs preferentially below, but not above, impermeable mudstones. These low- and high-permeability features suggest that pore-fluid flow was important during diagenesis. Fluid inclusions trapped in diagenetic quartz overgrowths formed between 68° and 94°C. This silica was probably supplied in solution from the temperature-driven illitization of smectitic clays surrounding these sandstones deeper in the basin. Fluid volumes from clay dewatering, from mechanical compaction, or from influx of overlying seawater were too small to transport diagenetic silica volumes. Silica-rich fluids were probably transported up-dip by convective cells within the sandstones and authigenic quartz precipitated as these fluids cooled. This episode of quartz diagenesis could have been completed within 1·6 × 106 yr if fluid velocities were 3·1 m/yr. Similar convective fluid flows could have transported the fluids responsible for secondary porosity development and the hydrocarbons expelled from mudstones later in the basin burial history.

An organo-clay composite was prepared by contacting Na-montmorillonite and humic acid in aqueous solution which was of variable pH. After freeze-drying the precipitate of the solution, the detailed structure of the humic acid-montmorillonite composite was observed. Transmission electron micrographs and electron diffraction patterns indicate that the composite which was formed under acidic conditions has a characteristic microstructure. Humic acid, a large organic molecule, is combined with bent or curled thin foils of montmorillonite to form a spherical aggregate. The X-ray diffraction pattern supports this observation and suggests that the montmorillonite is cleaved into thin flakes as a silicate layer. The composite formed under alkaline conditions was in the form of a thin plate or lath and had a similar morphology to that of montmorillonite. The difference in the microstructure of the composite is reasonably attributed to the chemical flexibility of humic acid, i.e., conformation changes depending on the pH of the solution.

Minerals studied by an equilibrium model with a single mineral are similar to those studied in solid-solution models with q end-members. After discussing solid-solution models with q end-members where the limits of this kind of models are specified, the mathematical relations between the two kinds of models are developed. These relations show that the equilibrium model with a single mineral is compatible with the geochemical assumption of solid-solution. A method for estimation of equilibrium between a single mineral and a homogeneous set of aqueous solutions is proposed.

Three-component interstratification of layer silicate minerals in the clay fractions of soils and sediments is probably more common than is generally realized. However, interpretation of the proportion and arrangement of the various components from experimentally recorded X-ray diffraction curves is difficult and in this paper a series of calculated diffraction patterns are presented which illustrate the types of diffraction patterns obtained from interstratified mica-vermiculite-montmorillonite systems.

The different rates of smectite illitization have been investigated in interbedded sandstone and mudstone samples from the Neogene to Lower Pleistocene stratigraphy of the Niigata sedimentary basin. For samples of approximately the same age and under the same temperature and pressure conditions, the analytical results of XRD and EDS show that differences in the transformation from R = 1 I-S to R≥3 I-S at a temperature of ~30–40°C and 1000 m in depth are determined by the initial smectite composition and the relative ion concentration of pore-fluid in the sedimentary rock system. The ordered I-S and illite in the mudstone have inherited compositional characteristics from the initial detrital smectite and illite. In the sandstone, the I-S composition was changed by interaction with pore-fluids and by precipitation and crystal growth during diagenesis.

Measurement of clay particle size invariably presents data in the form of equivalent spherical diameters. For asymmetric particles the equivalent spherical diameter varies with the method of measurement. Based upon an understanding of the theoretical concepts involved, a method has been proposed whereby comparison of data on a given sample from two different techniques can reveal information about the minor dimension of the particle. Theoretical expressions are given for the equivalent spherical diameter of cylindrically symmetric rods and discs from which it is shown that some of the existing measurement methods are more dependent upon size than the degree of non-sphericity whilst for others the reverse is true. It is shown how for rods and discs one can obtain information on both an average axial ratio and the distribution of this parameter for heterogeneous samples. Illustrated data are given for three kaolin samples. Far from showing inconsistency between the variable spherical diameters yielded by different instruments, the data produce compatible size and thickness parameters which match those observed in supplementary, unreported electron microscope experiments. A method of measuring particle major and minor parameter distributions is indicated.

Lors de l'étude des produits d'adsorption du benzène sur une montmorillonite cuivrique partiellement déshydratée (P4O10 et vide), la polymérisation du benzène en polyparaphénylène a été mise en évidence. Cette polymérisation a lieu au cours de cycles de déshydratation — adsorption — réhydratation à l'air, à partir de la forme rouge du complexe montmorillonite — cuivre II — benzène. Le polymère, caractérisé par spectroscopie infra-rouge, est formé dans l'espace interfoliaire de la montmorillonite comme le montrent les diagrammes de rayons X. Les mécanismes réactionnels possibles sont discutés.

Nous décrivons un montage expérimental permettant d'obtenir, avec une bonne précision, des diagrammes de diffraction X de poudre d'argile dans un état hydraté homogène et de suivre la cinétique du processus d'hydratation. Nous avons pu déterminer, dans le cas de l'état homogène à une couche d'eau d'une beidellite sodique, la position des cations échangeables, le nombre total de molécules d'eau par maille et leurs coordonnées z, en utilisant une méthode de modèle basée sur la comparaison des profils expérimentaux et calculés des réflexions 00l. De plus nous avons comparé les caractéristiques structurales et en particulier le mode d'empilement des feuillets de l'état monocouche avec celui des états anhydre et bicouche. L'analyse du profil des réflexions 00l montre l'existence de fluctuations autour d'un espacement basal moyen. Ces fluctuations sont interprétées comme provenant de l'hétérogénéité de la distribution des charges dans le feuillet. Enfin, un processus théorique d'hydratation et de déshydratation est proposé.

Les nontronites ne présentent pas les propriétés caractéristiques des phyllosilicates 2:1 magnésiens ou alumineux à substitutions tétraédriques: domaines d'hydratation homogène, isotherme de désorption d'eau avec paliers, organisation structurale ordonnée ou semi-ordonnée. Or les analyses structurales montrent que ce sont des beidellites ferriffères et l'étude de l'effet Hofmann–Klemen confirme le taux très faible de lacunes et de substitutions octaédriques. Diverses hypothèses justifiant ces propriétés sont présentées et discutées.

The weathering of a trachytic pumice within a pyroclastic flow underlying an andic-brown soil on the volcano Vico has been studied. The main mineral formed is a spherical 10 Å halloysite which has been shown by SEM and in situ microprobe analysis to have formed directly from the glass. The major mineralogical characteristics as determined by XRD, IR, DTA, TEM and microdiffraction are typical of 10 Å halloysite. However, some minor mineralogical properties and the high Fe and K contents, suggest that it is an interstratification of 74% halloysite and 26% illite-smectite. The calculated formula of the hypothetical 2:1 minerals reveals an Fe- and K-rich clay, with high tetrahedral substitution, like an Fe-rich vermiculite, but the detailed structure of this mineral remains uncertain.