An intergradient 14 Å mineral showing X-ray diffraction features of “chloritized” vermiculite in a Korean Ultisol was studied. The structural formula of the whole 2:1 layer-silicate (14 Å mineral and mica) in the Na+-saturated 0·2–0·5 µm fraction was obtained by elemental, thermogravimetric and 29Si and 27Al nuclear magnetic resonance spectroscopic analyses in combination with extraction of the interlayer material from the 14 Å mineral by hot 1/3 m sodium citrate treatment. This formula showed: (1) the 2 : 1 layer contains nearly one Al3+ in four tetrahedral positions, and Al3+ is the dominant cation in the octahedral sheet; (2) K+, exchangeable Na+ and sodium citrate extractable 1 : 1 layer occupy the interlayer space of the 14 Å mineral in similar proportions. Very little interlayer K was replaced by Na+ during the citrate treatment. Possible schemes of alteration of the 2 : 1 layer to the 1 : 1 layer as its interlayer material are discussed.

The Kämpf & Schwertmann (1982) procedure for concentrating iron oxides in soil clays by dissolution of kaolin and gibbsite by boiling for 1 h in 5 m NaOH may not dissolve all kaolin, and also results in the precipitation of sodalite. For the complete dissolution of kaolin in kaolin-rich soil clays a boiling time of 2 h in 5 m NaOH was required. The large amounts of sodalite produced were not removed by the prescribed single wash in 0·5 m HCl. Oxalate soluble Al contents of iron oxide concentrates were sometimes very high and dithionite Fe contents were very low both in concentrates containing sodalite, and in those for which sodalite was not detected by XRD, but where a previously unsuspected amorphous sodalite-like phase may have been present. Complete removal of precipitated sodalite was achieved by two extractions with 0·5 m HCl at 25°C for 20 min. This modified procedure does not alter the Al-substitution and crystal size of goethite, hematite and maghemite as determined by XRD measurements.

Four 15 g samples of an unsedimented Wyoming bentonite were treated with 200 cm3 of 0·025, 0·050, 0·100 and 0·250 mol dm−3 H2SO4 for 1 h at room temperature (samples I–IV, respectively). Three further 15 g samples were treated with 200 cm3 of 50% (v/v) H2SO4 for 1 h at 20°C (sample V), and 1 and 2 h under reflux (samples VI and VII, respectively). X-ray fluorescence and diffraction studies revealed that only samples VI and VII suffered any substantial structural attack. The resulting acidity of the clays, determined by cyclohexylamine desorption, indicated that sample V contained the largest number of protons at 0·59 mmol H+ (g clay)−1. Sample V was also the most efficient catalyst for the dehydration and etherification of hexan-1-ol, giving a combined product yield of 17·0% after 2 h reflux in neat reactant. The parent bentonite and samples I and II showed no discernible catalytic activity despite measured acidities of 0·1, 0·24 and 0·34 mmol H+ (g clay)−1. In contrast samples III and IV gave combined product yields of 4·5 and 11·0%, respectively, which correlated well with the measured acidities of 0·38 and 0·48 mmol H+ (g clay)−1. Samples VI and VII, prepared by reflux in acid, contained 0·3 and 0·1 mmol H+ (g clay)−1, respectively, and gave combined product yields of 13·0 and 6·0%.

The acidity of Ni2+- and Co2+-exchanged montmorillonite has been probed using the diagnostic bases n-butylamine, cyclohexylamine and pyridine. Derivative thermograms for the desorption of pyridine from Ni2+- and Co2+-exchanged montmorillonite exhibited strong maxima at 40°, 90° and 360°C together with a weak maximum near 170°C The desorption maximum at 360°C is usually attributed to desorption of base from Bronsted acid sites. However, IR spectra of pyridine adsorbed on Ni2+- and Co2+-exchanged montmorillonite, at 250°C were dominated by intense bands near 1450 and 1607 cm−1 which are diagnostic of Lewis-bound pyridine. Consequently, the desorption maximum at 360°C must, in this instance, be attributed to desorption of pyridine from Lewis acid centres. Other bases, including cyclohexylamine and butylamine, also desorb at temperatures which have previously been attributed to the desorption of protonated base. Ni2+- and Co2+-exchanged clay contained predominatly Lewis acid or electron accepting sites, which is in marked contrast to the behaviour of trivalent cation exchanged clays.

The thermal behaviour of sepiolite and palygorskite treated with pyridine (Py) was investigated by DTA, TG, DTG and EGA (by MS) under a flow of air and inert gases (N2 or Ar). The thermal analysis showed that the organic base was adsorbed by the clays, penetrating into the clay pores and replacing zeolitic and bound water. Its presence in the pores shifted the dehydroxylation peak to temperatures higher than the corresponding peak in the untreated clays. Under N2 and Ar, thermal desorption of Py from sepiolite was observed at 260 and 650°C whereas for palygorskite only traces of Py were detected in the evolved gases. In addition to desorption, reactions of pyrolysis and condensation to coke were detected by the evolution of ammonia, methane and hydrogen, respectively. In air, oxidation of the organic matter led to the appearance of exothermic peaks. The profile of the DTA curve and the temperatures of the most intense exothermic peaks were determined by the rate of the carbon oxidation.

Desautelsite, a Mg(II)Mn(III) hydroxy carbonate first described in 1979 and represented by the general formula Mg(8−x)Mn(III)x(OH)16(CO3)x/2 (in which 2 < x < 2·67), has been synthesized under controlled pH conditions (induced hydrolysis) and coprecipitation techniques. In the pH-stat syntheses, the desautelsite is formed by aerial oxidation of MnCO3 in 0·05–0·15 m Mg(NO3)2 solutions at ∼pH 9 and temperatures of 35°C where, in the absence of Mg, manganite would normally form. The synthesis product from this technique is generally more crystalline than that formed by the coprecipitation method. Composition, particle shape and aggregation may be controlled through variations of the Mg concentration, pH, aeration rate or temperature. Indirect evidence suggests Mn to be present in the +3 oxidation state in the desautelsite.

The EDTA-insoluble residues from five samples (two from the oolitic shoal facies and three from the lagoonal facies) of the Late Permian Ca-2 unit (Zechstein) have been investigated by X-ray diffraction, infrared spectroscopy, and scanning and transmission electron microscopy with energy dispersive X-ray analysis (EDXA). The results show that spheres of non-crystalline hydrous feldspathoids (with Al/Si molar ratio between 1·5 and 2·2) dominate the residues of samples from the oolitic shoal facies. Samples from the lagoonal facies are dominated by crystalline material (muscovite and quartz), but two of the samples contain a small number of spheres. Analyses of these samples by selective area diffraction and EDXA revealed the presence of small amounts of non-crystalline hydrous feldspathoids with Al/Si molar ratio between 0·1 and 1·9.

X-ray diffraction was used to analyse the distribution of clay minerals in the <2 µm fraction of the lutitic and marly facies from the centre of the Basque-Cantabrian Basin (Basque Arc), where the sedimentary section is 2000 to 10,000 m thick. Most of the deposits were laid down during the Cretaceous and Paleogene and were related to the opening and closing of the Bay of Biscay. The most noteworthy variations are in kaolinite, smectite and mixed-layered (R = 0, R = 1 and R ≥ 3) illite-smectite, which can be ascribed both to provenance and to diagenesis. A general diminution in expandability is related to the gradual transformation of smectite to illite from south to north, and with depth. Temperature, residence time and chemical activity during diagenesis are the factors that had greatest influence on the changes in the original mineral assemblages inherited from the source area. On the basis of the clay minerals and the Kübler index, a general scheme is proposed for the diagenetic evolution of the area from the initial stages to anchimetamorphism.

Grain-size distribution, specific surface, thermal analysis, electron microscopy and X-ray diffraction were used to study the effect of dry grinding on the structure and properties of two kaolins of different degree of crystallinity. Grinding caused particles to fragment and resulted in the formation of stable large spheroidal aggregates of fine particles. These two processes were not clearly separated by a specific grinding time, but occurred in parallel shortly after grinding was started, although aggregate formation persisted at longer grinding times. The variation in the specific surface area during grinding was found to be dependent on these two processes and on the particle size and crystallinity of the initial kaolin. DTA and XRD data and the amount of water released at different temperatures revealed grinding to gradually destroy the kaolinite structure and cause the loss of hydroxyl ions and the formation of others that were subsequently removed at low and medium temperatures. An explanation for the process whereby the new hydroxyl ions are formed is provided.