Porosity development in a sepiolite from Toledo, Spain, has been studied as a function of acid (0·25, 0·50, 0·75 and 1·0 m HNO3) and subsequent heat treatments (110–400°C). Adsorption isotherms of N2 at 77 K have been analysed by f-plot, t-plot, αs-plot and the Cranston & Inkley methods. Results are compared with those obtained on products heated without previous acid activation. Experimental conditions favouring porosity development are discussed.

The reactions of ten C6-alkenes over a Cu2+-montmorillonite catalyst have been examined between room temperature and 100°C. The reaction products depend upon inter alia the branching in the alkene, the position of the double bond, and the temperature. Hex-2-ene, cis and trans-4-methyl-pent-2-ene and 4-methyl-pent-1-ene do not react at all, whereas 2-methyl-pent-1-ene and 2-methyl-pent-2-ene and 3,3-dimethyl-but-1-ene form alcohols below ∼40°C and dimers at higher temperatures. Hex-1-ene forms the di-2,2′-hexyl ether.

Eleven shales and fourteen turbidite sandstones from the Mam Tor Beds were analysed chemically and by XRD. The ratio of kaolinite to illite plus mixed-layer clay was higher in the sandstones than in the shales, size fractions demonstrating that this ratio decreased as the grain size decreased. Shales more basinal in character than those of the Mam Tor Beds contain more illite and mixed-layer clay and less kaolinite and it is suggested that there was a lateral variation in clay mineralogy with distance from the shore line due to particle size sorting and that the character of the clay mineral fraction was retained as the turbidity current transported sediment from a nearshore environment deeper into the basin. Support for this model was obtained from the geochemistry which showed that the sandstone matrix differed compositionally from the shales. Systematic variations occurred in the turbidite sandstones but not in the shales which are therefore considered to be non-turbiditic. Only minor mineralogical changes appear to have occurred during diagenesis.

Two chlorites, sheridanite and clinochlore, have been examined to determine their surface charge characteristics. In order to increase their surface area and to produce a measurable surface charge, the chlorites were treated with 10−3m, 10−2m, and 10−1m HCl in 10−2m MgCl2 solutions. These treatments are shown not to alter the crystallinity of the chlorites and to produce a small pH-dependent negative charge which is not directly related to the total surface area. The clinochlore, (Si6.13Al1.84)(Al1.53FeIII0.53FeII0.18Mg9.52)O20(OH)16, is more readily attacked by the acids than the sheridanite, (Si5.43Al2.55)(Al2.90FeII0.05Mg8.86)O20(OH)16, and also produces material with greater surface area and pH-dependent, negative, surface charge. It is concluded that: (i) isomorphous substitutions in the lattice are not reflected in a permanent surface charge; (ii) the observed surface charge arises not only at the edges of the particles but also at points where the chlorite is predisposed to attack by acids; (iii) in the chlorite-acid system used, anions—probably mainly silicate—block positively charged sites.

A method for estimating Gibbs free energies and stabilities of clay minerals is proposed for use with computer programs aimed at calculating the chemical evolution of natural water-rock systems. This is based on (i) a model for ideal solid solutions of a large number of end-member compositions and (ii) a data set of estimated solubility products from 36 end-members. The application of the method to the production of experimental or natural clay stabilities is discussed.

Hematites obtained by heating goethite gave different IR absorption spectra depending on the temperature of formation. Hematites formed between 250–600°C consisted of lath-like crystals (average size 0.4 ×0.08 µm) and showed, in accordance with theoretical predictions, very similar IR spectra whose absorption bands could all be assigned to surface mode vibrations. However, significantly different IR spectra were given by hematites formed between 700–950°C, the differences being correlated with variations in the size and shape of the particles. Differences observed in the IR spectra of powder hematite do not therefore justify new names for the mineral, as have been proposed in the literature.

A method is described for calculating, and then subtracting, the background from X-ray diffraction patterns of oriented clay mineral samples. Ti-Kα radiation is used and, to minimize the absorption of this radiation by air, a vacuum and helium-flushed device has been developed. This device can be used with other X-ray sources, offering a considerable increase of intensity—e.g. Co-Kα radiation is increased by 125%. With the background-eliminated patterns a better semi-quantitative estimate of the composition of clay mineral mixtures is possible. Small differences in composition of two samples can be identified by subtracting one of the background-eliminated patterns from the other. Using this method, peak maxima of smectite-group minerals can also be accurately determined.

Well-crystallized kaolinite was found to exhibit marked proton conductivity at pre-dehydration temperatures. Direct current conductivity and thermopotential measurements were performed. By comparing the results obtained with Au electrodes (proton blocking) to those obtained with Pd electrodes (proton injecting), non-protonic contributions could be separated from proton conductivity. The majority charge carriers appeared to be defect proton (negative sign), corresponding chemically to an O2− replacing OH− in the lattice, but excess protons were also noted (positive sign). Below 275°C the activation energy was of the order of 7–8 kcal mole−1; between 275–450°C it was about 18–20 kcal mole−1. This indicated a two-step defect proton-excess proton conductivity mechanism involving, in succession, the two kinds of OH− in the kaolinite structure: (i) OH− located within the six-membered ring formed by the SiO4 tetrahedral sheet, (ii) the close OH− array formed by the octahedral sheet. The conductivity results were supported by IR spectroscopic measurements.