The clay mineral composition is one of the factors that affect the physical properties of soils, and a knowledge of it is required to promote a fuller understanding of the origin of these properties. The relationships between the clay content and the plastic and liquid limits of natural montmorillonitic and kaolinitic soils and of artificial mixtures have been examined and compared. Factors affecting the relationships are discussed, and illustrated by the effect of particle aggregation on the measurement of the liquid limit of tropical red clays and on the sedimentation analysis of the Keuper Marl. The effect of muscovite and of silt-sized material on the position of soils on the Casagrande classification chart has also been examined.

The general approach to the problem of the real structure of smectites requires an analysis based on the relationship between structural characteristics and diffraction patterns. This paper, which considers only the models corresponding to dioctahedral smectites saturated by K-cations and collapsed, includes: 1. Successive consideration of all models which are crystallochemically possible. These models may differ in (i) the structure and chemical composition of layers and interlayer spaces; (ii) the azimuthal orientations, translations and the mode of alternation of the layers; (iii) independent parameters which describe quantitatively the models (e.g. abundance of each type of layer, probability parameters defining the succession of layers, …). 2. Calculation, in all accessible domains of reciprocal space, of the distribution of intensities and profile variations, obtained by changing only one parameter at a time, that defines one type of structural feature (e.g. cation distribution in individual layers, stacking of the layers, nature of stacking faults, …). 3. A systematical analysis of the calculated diffraction patterns to establish the diffraction criteria which will help to interpret the experimental data explicitly.

A number of thermodynamic properties were obtained from the determination of adsorption isotherms and enthalpies of immersion for systems with water and Na- and Ca-bentonites. Entropy differences were calculated by combining the enthalpies of immersion and the changes in free energy derived from the adsorption isotherms. The swelling pressures, also calculated from the water adsorption isotherms, are in satisfactory agreement with the experimental data.

China is a significant producer of kaolin with 2.1 Mt in 2002 representing 8.4% of the world's total of 24.9 Mt. The kaolin resources are widespread throughout the country and are varied in their origin, physical and chemical properties and morphology. The kaolin industry, compared to Europe and the USA, is fragmented with no single large company. In 2002, China was the world's largest producer of ceramics, particularly for sanitary ware and porcelain. Also, China is now the second largest producer of paper and paperboard in the world. The quality of kaolin and halloysite is suitable for ceramics with no need to import. However, the quality of existing paper/ board-coating clays is not up to the quality of imported material from Brazil and the USA and there is an urgent need to develop local resources to meet the present and future demands of the market.

Three duricrust types (calcretes, palycretes and silcretes) have been distinguished in the Lower Paleogene arkosic materials from the margins of the Duero and Tajo basins (central Spain). In the calcretes the cements are composed of calcite plus palygorskite, whereas palygorskite is the only cement in the palycretes. In the silcretes, the cement consists chiefly of opal and chalcedony, with minor quartz. The important duricrust development in the Paleogene detrital materials can be correlated with a drastic climatic change towards colder and more arid conditions during this time, as inferred from the sedimentological features and the clay mineral evolution. The origin of calcretes and palycretes is related to the movement of alkaline phreatic waters generated from dolomitic rocks of Cretaceous age cropping out in the near surroundings. Silcretes originated from the vertical transfer of silica from supersaturated groundwaters, from the Hercynian granitic rocks, up to the surface. Silcretes are developed either on unconsolidated arkosic materials or replace previous calcrete or palycrete levels.

Silico-ferric coprecipitates, with chemical formula , were aged in suspension at 75°, 100° and 150°C and the structural evolution of solids with time studied by XRD, TEM, and IR, Mössbauer and EXAFS spectroscopy. The initial Si-Fe coprecipitate was found to be amorphous but showed local order similar to that of a smectite layer. At 75°C only a weak structural evolution of the silico-ferric product towards a smectite-like structure was observed. Experiments performed at 100° and 150°C led to synthesis of a ferric smectite with structural formula . During syntheses a highly soluble silico-ferric complex appeared; the Si/Fe atomic ratio of this complex was 3, and the apparent concentration of Fe3+ in solution reached 27 mm/l. These syntheses prove that the crystallization of a dioctahedral smectite, containing only Fe3+ atoms in the octahedral sheet, is possible under strictly oxidizing conditions. However, crystal growth of a ferric smectite under these conditions is slow and only syntheses carried out at sufficiently high temperatures give convincing results.

Raman microscopy of the kaolinite polymorphs was used to study single crystals and bundles of aligned crystals of kaolinite. The spectra of the hydroxyl stretching region were both sample and orientation dependent. Kaolinites can be classified into two groups according to the ratio of the intensities of the 3685 and 3695 cm−1 bands. No relationship was found between the d-spacing and the crystal domain size measurement from the 001 reflection and the Raman spectral intensities indicating the Raman spectra are independent of d-spacing and crystallinity. However, a relationship of the crystallinity in the a-b direction and intensities of the 3685 and 3695 cm−1 bands indicate that the relative position of one layer to the other determines the position of the inner surface hydroxyl groups and the hydrogen bonding with the oxygen of the opposite layer. A new hypothesis based on symmetric and non-symmetric hydrogen bonding of the inner surface hydroxyl groups is proposed to explain the two inner surface hydroxyl bands centred at 3685 and 3695 cm−1. The bands at 3670 and 3650 cm−1 are described in terms of the out-of-phase vibrations of the in-phase vibrations at 3695 and 3685 cm−1.

The soils of Scotland are relatively young, being developed mainly on glacial drift deposited some 10 000 years ago. Only a small number of genetic soil types are represented, but this is more than compensated for by the wide variety of parent materials from which the drift ultimately derives. The major parent materials include granite and granitic gneiss, gabbro, basalt/andesite, mica-schist and related metamorphic rock types, Lower Palaeozoic greywackes and shales, Old Red Sandstone sediments, Carboniferous sediments, fluvioglacial sands and gravels, and estuarine silts and clays. The clay mineralogy of the soil associations developed on these parent materials is described and the origin of the clay minerals is interpreted. It is concluded that the influence of inheritance is predominant, but that the effects of pre-glacial weathering and Holocene pedogenesis can also be discerned. Inheritance has contributed a wide variety of clay minerals to the soils, including illite, kaolinite, chlorite, smectite and a number of interstratified minerals, pre-glacial weathering has resulted in the widespread formation of kaolinite and halloysite, irrespective of soil parent material or drainage class, and recent pedogenesis has brought about the transformation of inherited layer silicates by vermiculitization processes, with concomitant interlayer alumination, particularly in surface horizons.

Nous proposons l'étude du mècanisme de gonflement d'une smectite, basée sur l'exploitation des diagrammes de diffusion aux petits angles obtenus avec la source de rayons X synchrotron de Lure (Orsay). Cette technique a permis d'étudier le gonflement, en fonction de la température, d'une montmorillonite Na, en suspension dans l'eau et concentrée à 20%.

L'analyse des diagrammes est éffectuée par une méhode basée sur la comparaison des courbes expérimentales à des courbes théoriques. Les modèles de structure permettant le calcul des diagrammes théoriques fait appel à la notion de particule (définie comme un empilement de feuillets parallèles) et de structure interne de la particule (définie par un ensemble de translations di affectées des probabilités pi qui déterminent la position mutuelle des feuillets).

Les résultats montrent qu'à basse température, les particules de très grande taille sont constituées par la superposition de sous empilements, comportant 4 à 5 feuillets, hydratés d'une manière homogène et se désorientant mutuellement pour former la structure du gel. On explique ainsi que la structure du gel formé est correlée avec celle du solide initial et que le phénomène de gonflement est quasi réversible.

During the reaction of solutions of the leuco dyes crystal violet lactone and N-benzoyl leuco methylene blue with acid-treated montmarillonite (as occurs with carbonless copying papers), most of the offered dye is intercalated within the interlayers of the montmorillonite structure remaining after acid attack. This phenomenon was demonstrated by XRD and also by high-resolution transmission electron microscopy. During acid treatment, octahedral cations are dissolved from exposed edges of the montmorillonite lamellae and amorphous silica builds up in these areas. As a result, the BET(N2) specific surface area increases from ∼60 m2/g to ∼300 m2/g and, consequently, the theoretical reactivity towards leuco dyes. Nevertheless, only small quantities of the dye molecules are adsorbed onto the amorphous silica. The excellent colour intensity and, in particular, the resistance to fading in the light of the montmorillonite dye complexes may be explained by the protected position of the dye molecules within the interlayers of the montmorillonite.

Aluminous hydroxy 2/1 clay minerals (‘intergrades’) can form in two ways: Al can either come externally from the solution, or internally from the mineral itself (octahedral or tetrahedral layers). This study is more concerned with the latter which seems the main source in acid soils.

The most common organic acids present under natural conditions were used on two trioctahedral micas (phlogopite and biotite), and their chemical and mineralogical weathering effects were determined.

Different kinds of mineralogical evolution are possible: mineral destruction by a few very complexing acids, possibly with intermediate stages (interstratified minerals); formation of ‘transformation’ smectite by acids derived from sugars; Al-hydroxy vermiculite formation (the 14 Å diffraction peak of which is stable under K saturation and vacuum). This evolution is the most frequent and is produced by the most numerous organic acids (even CO2), the acidity of which results in Al migration in the interlayer, but the complexing ability of which is not sufficient for Al removal.

The pillaring of a Laponite by alumina pillars, iron pillars and mixed Al-Fe pillars was obtained by a simple in situ method starting from AlCl3 and/or FeCl3 solutions with different molar ratio Fe/(Fe + Al), and from NaOH solution added simultaneously to the clay suspension. The Al13 pillars were evidenced by XRD and NMR spectra. The density and the charge of these pillars were calculated from the chemical analysis. The Fe pillars (in samples with Fe content >26%) are larger than Al13 pillars and slowly reducible by hydrogen temperature programmed reduction (H2TPR), but we do not have any information on their structure. There is also an excess of non-pillar Fe retained by the pillared clays probably as oxyhydroxides. The isomorphic substitution in the mixed (Al-Fe)13 pillars (in samples with an Fe content >26%) was evidenced by H2TPR results compared to the chemical analyses and by the interpretation of the 27A1 peaks in the NMR spectra.

An Fe-rich smectite from Ölberg (Germany) was characterized using X-ray diffraction, infrared spectroscopy and analytical electron microscopy. Progressive reduction of the octahedral charge was performed through the Hofmann & Klemen effect at increasing temperatures. The sample was heterogeneous, consisting of two smectite populations. One population, which comprises a minor portion of the sample, is an ‘Fe3+-montmorillonite’ with little or no tetrahedral charge and Fe3+ as the major octahedral cation. The other population, a major constituent of the sample, contains less Mg and more Al than the first one and exhibits some tetrahedral charge. This fraction may be considered as an inter-grade between nontronite (dominant tetrahedral charge) and Fe3+-montmorillonite (dominant octahedral charge). These two populations may occur as separate particles but also as interstratified layers.

Twenty one samples of relatively pure tubular halloysites (HNTs) from localities in Australia, China, New Zealand, Scotland, Turkey and the USA have been investigated by X-ray diffraction (XRD), infrared spectroscopy (IR) and electron microscopy. The halloysites occur in cylindrical tubular forms with circular or elliptical cross sections and curved layers and also as prismatic tubular forms with polygonal cross sections and flat faces. Measurements of particle size indicate a range from 40 to 12,700 nm for tube lengths and from 20 to 600 nm for diameters. Size distributions are positively skewed with mean lengths ranging from 170 to 950 nm and mean diameters from 50 to 160 nm. Cylindrical tubes are systematically smaller than prismatic ones. Features related to order/ disorder in XRD patterns e.g. as measured by a ‘cylindrical/prismatic’ (CP) index and IR spectra as measured by an ‘OH-stretching band ratio’ are related to the proportions of cylindrical vs. prismatic tubes and correlated with other physical measurements such as specific surface area and cation exchange capacity. The relationships of size to geometric form, along with evidence for the existence of the prismatic form in the hydrated state and the same 2M1 stacking sequence irrespective of hydration state (i.e. 10 vs. 7 Å) or form, suggests that prismatic halloysites are the result of continued growth of cylindrical forms.

Large quantities of clay minerals (and other micron-sized mineral powders) are used widely in materials science. Mineral fillers are major components, for example, of paints, rubber, plastics and paper and board. While the original object of such incorporation was to reduce costs, performance is now being “engineered” by design or choice of the relevant mineral particles. This paper concentrates on the use of mineral powders in polymer and paper science. In both application areas, the size and shape of the mineral particles can affect mechanical properties such as stiffness and tensile and impact strength. However, other characteristics are also modified. For example, the drainage rate in paper formation and the rheology of a polymer melt, properties which are critically important to the rate of processing of the relevant materials, can be greatly affected. Finally, the size and shape of the mineral particles also affect appearance, i.e. the smoothness, uniformity, optical properties etc. Mechanical and rheological data are presented for mineral-filled polypropylene, as are mechanical and optical data for filled and coated paper.

Di- and trioctahedral micas were altered to vermiculite-like minerals by extracting the K with sodium tetraphenylboron. Chemical analysis of original and altered micas shows that loss of K is accompanied by an increased loss on ignition, oxidation of some Fe2+ to Fe3+, loss of divalent octahedral cations, mainly Mg2+, loss of OH− (or sorption of H+) and decrease in net negative charge.

The following reactions are suggested to explain these changes: (1) replacement of K by Na at interlayer sites; (2) release of structural OH− ions exposed by replacement of K, which decreases the negative charge and allows the structure to expand and more K to be replaced; (3) oxidation of Fe2+ ions by the reaction

4Fe2+ + 4 structural (OH−) + O2 → 4Fe3+ + 4 structural (O2−) + 2H2O;

and (4) release of divalent octahedral ions, possibly through some of the holes left when structural OH− is lost.

The wide implications of these proposals are discussed.

The IR spectra of -saturated smectites were examined in terms of their charge characteristics. The υ4 band near 1440 cm-1, observed in the DRIFTS spectra (obtained without use of a KBr matrix), was assigned to the vibrations of ions compensating the negative charge of the clays. When KBr was used as a diluting matrix, the υ4 band was located at 1400 and/or 1440 cm-1. The band at 1400 cm-1, related to NH4Br, originated from the replacement of in the clay by K+ from the KBr. For swelling clay minerals this band indicates that layers have permanent low charge density and/or variable charge. For non-swelling clay minerals, the 1400 cm-1 band characterizes the presence of variable charges only. The υ4 band at 1440 cm-1 suggests that in the clay was not replaced by K+ from KBr and remains in the interlayer space of the clay minerals. This absorption is due to compensating only permanent charge in the interlayers, or part of the interlayers with a high charge density. The presence of both bands at 1400 cm-1 and 1440 cm-1 in the IR spectrum suggests that the clays studied have a heterogeneous interlayer charge.

Close relationships are demonstrated between reservoir quality, lithofacies, provenance and burial history in the Jurassic Brent and Viking Groups in the Norwegian North Sea. Porosity and permeability are strongly and systematically related to the initial texture and composition of the sandstones. Porosity variations are related to the amount of compaction, which is more severe in matrix-rich than in clean facies, and quartz cementation, which is most important in clean facies. Permeability variations are related to porosity and facies-controlled variations in grain size, and abundance and texture of intergranular fines. Illitization of early diagenetic kaolins require K, which is derived mainly from dissolution of K-feldspar. Sediments were sourced from K-feldspar- poor provenances during the maximum progradation of the Brent Group, and sandstones deposited at this time are less exposed to illitization and have better permeability at deep burial than reservoir sandstones that initially contained more K-feldspar.

Existing data on interatomic potentials have been used to study the interactions between an uncharged clay sheet and a water molecule. Calculations show that most of the clay surface is relatively hydrophobic, with binding energies for a water molecule in the range 1·0–4·5 kcal mol−1. There is, however, a low-energy site for an oriented water molecule above the layer OH group and within the ring of six SiO4 tetrahedra. Using two different models for the interactions, the binding energy in this position is found to be either 13·2 or 21·8 kcal mol−1. The existence of the low-energy site accounts for the formation of the hydrated ‘10 Å’ phase of talc, which is known from high-pressure experiments. Data on the PT stability of this phase can be used to estimate its energy of dehydration. This quantity is shown to be consistent with the value of 21·8 kcal mol−1 for the binding energy of a water molecule and the energy associated with the expansion of the layers from the 9·35 Å phase.