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.

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.

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.

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.

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.

Experiments on the conversion of feldspar to illite reveal that variation of the fluid/rock ratio (flow rate) has a significant effect on the kinetics of feldspar dissolution and illite formation. Dissolution of albite in near-neutral KCl solution at 200°C and 500 bar shows that the Si and Na release rate per unit surface area of albite is faster with higher fluid/rock ratio. These results have application to the interpretation of secondary porosity formation. The experiments also reveal a special set of conditions under which rapid illite formation can occur. In contrast to the slow process of illite formation in neutral solution, there can be mass nucleation and growth of illite platelets on albite surfaces in an initially acidic solution with low fluid/rock ratio. In similar experiments with higher fluid/rock ratio, kaolinite forms instead of illite because there is insufficient solid to titrate the large volume of solution. This study suggests that illitization of feldspar or kaolinite may be triggered by a decreased rate of acidic fluid-influx during burial diagenesis.

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.

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.

The literature on the complexes of n-alkylammonium ions with layer silicates is characterized by marked divergences, not only in the deductions and conclusions of the different investigators but also in their experimental results. An attempt is made to reconcile and rationalize the differences, and to form a self-consistent picture of these systems.

Given a saturating solution of sufficient concentration, the complexes tend during their formation to adopt an arrangement in which silicate layers are separated by double layers of ions oriented so that the alkyl chains are extended away from the silicate surfaces at a high angle. Water molecules, salt and free alkylamine may also be present in the interlayer spaces. When the excess material is removed by washing and the complexes dried, ideally the alkyl chains from opposing surfaces move over one another and interpenetrate so as to form a single layer of ions. During the contraction, however, the chains interact with one another and tend to stick at some point short of complete interpenetration. Weak attractive forces acting to bring the silicate layers together, and consisting mainly of electrostatic forces originating in the mineral layers and van der Waals interactions arising from increasing association of opposing alkyl chains with increasing interpenetration, are insufficient to overcome this tendency fully. As a result, an alkyl chain of given length can give rise to a series of complexes differing in their XRD characteristics.

Previous workers have noted the difficulty of achieving reproducible results and some have recommended grinding the complexes, but it appears that this treatment significantly alters the nature of the end-product.

The textural evidence in septarian concretions shows that the septa formed as tensile fractures during burial and compaction of the host shale. Comparison of the combinations of vertical and horizontal stresses and pore-fluid pressure required for tensile fracture of cemented concretions and those likely to occur during shale burial indicates that septarian fracturing will be favoured by overpressuring and low horizontal stress, most likely to occur during times of rapid burial. Burial histories of septarian concretions from the Eocene London Clay and the Jurassic Kimmeridge Clay show that fracturing can form under as little as 50 m of sediment. By relating episodes of septarian fracturing to times of rapid burial, the timing of diagenetic cement formation can be constrained.

Different forms of structural and chemical heterogeneity are considered including mixed-layer minerals, disordered layer structures containing rotational and translational stacking faults, interstratification of trans-vacant (tv) and cis-vacant (cv) layers in true micas, illites and illitesmectite (I-S), short-range order in isomorphous cation distribution etc.

Because determination of various structural and chemical imperfections requires elaboration of new diffraction and spectroscopic methodologies, special attention is paid to recent achievements in the development of new methodological approaches such as a multispecimen simulation of experimental X-ray diffraction (XRD) patterns from mixed-layer minerals, with account taken of layer-thickness fluctuations of the second type and possible difference between structures of outer and core layers; experimental determination of thickness distribution of illite crystals by HRTEMand the modified Bertaut-Warren-Averbach technique; XRD and thermal methods for determination of cv and tv layers in true micas, illites and I-S; generalization of Méring's rules to account for the behaviour of non-basal reflections for any defective structure in which two translations are irregularly interstratified; various ab initio calculations devoted to modelling infrared OH vibrations, octahedral cation distribution in dioctahedral 2:1 layer silicates, etc. It is shown that these recentlydeveloped methodologies have revealed new diversity in the structural and chemical heterogeneity of phyllosilicates and clay minerals, provided new insight into the structural mechanisms of their transformation in different geological environments, and discovered new natural processes.

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.

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.

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.

The fluorine route is thoroughly investigated for the hydrothermal synthesis of montmorillonite in the Na2O-MgO-Al2O3-SiO2-H2O system. Using the optimal conditions suggested by Reinholdt et al. (2001) for the crystallization of pure montmorillonites with the formula Na2x(Al2(1-x)Mg2x☐)Si4O10(OH)2, several parameters (x, Mg content, duration of crystallization, F/Si atomic ratio, pH, nature of counterbalance cation) are varied independently from their ideal values. The products are analysed by various techniques (X-ray diffraction, thermogravimetric analysis-differential thermal analysis, 29Si, 27Al and 19F magic angle spinning-nuclear magnetic resonance). It appears that a pure montmorillonite can only be obtained within a narrow x range (0.10 ≤ x ≤ 0.20). The presence of F in the starting hydrogel and the crystallization time also have significant effects on the purity of the final products. It is shown that a small amount of fluorine is needed for the crystallization of pure montmorillonite phyllosilicates.

Die kristallchemischen Strukturformeln von 2:1-Schichtsilikaten werden unter Voraussetzung der idealen Struktur mit 22 negativen Ladungen von 10 Sauerstoffen und 2 Hydroxylgruppen berechnet. Für die Verteilung der 22 Kationenladungen auf Tetraeder-, Oktaeder- und Zwischenschichtpositionen werden unter Berücksichtigung der direkt gemessenen Zwischenschichtladungen (Lagaly & Weiss 1971) bzw. Kationenumtauschkapazitäten Voraussetzungen und Berechnungsregeln angegeben. Als Beispiele werden die Formeln eines Glaukonits und eines Nontronits berechnet.

Die Verteilung der Kationenladungen in der Kristallstruktur von 2:1-Schichtsilikaten wird am besten in einem Dreiecksdiagramm mit den Ecken Pyrophyllit-Seladonit-Muskowit dargestellt. Jeder Punkt im Dreieck stellt die gesamte Kationenladung in der Formeleinheit gleich 22 dar. Es ist die Summe der Ladungen aus Tetraeder-, Oktaeder- und Zwischenschichtkationen.

One of today's big challenges is to store safely the increasing amount of high-level radioactive waste (HLRW) in the world. In some of the concepts devised for this challenge, bentonite, a natural swelling clay, plays a key role in encasing the canisters containing the waste. The use of bentonite as a geotechnical barrier in HLRWrepositories is a new venture; specifications to ensure either optimum performance or that a minimum standard is reached at least do not exist yet. The present study summarizes relevant research and discusses possible HLRW-bentonite specifications. The importance of these specifications for any given repositories has to be assessed on a case by case basis, depending on the concept being employed and any special circumstances for the individual repositories.

Ten key issues were identified which were used to discuss bentonite specifications. In some of these key issues the optimum bentonite performance depended more on processing and production (compaction) than on the bentonite type (e.g. swelling pressure and thermal conductivity). In contrast, in some of the other key issues, the type of bentonite was found to influence possible specifications: the bentonite should not alter its mineral composition or its geotechnical parameters such as the swellability. Therefore, the bentonite should contain neither soluble nor reactive phases (e.g. organic matter, pyrite, gypsum). The structural Fe content of the smectites should be small because of the lesser stability and greater reactivity of the Fe-rich bentonites. Also, a large layer-charge density of the swelling clay minerals leads to less corrosion at the iron–bentonite interface (relevant if iron canisters are used). The hydraulic conductivity and swelling pressure can be tailored by compaction of the bentonite resulting in different dry densities. From an engineering point of view, a bentonite with least dependence of the hydraulic conductivity/swelling pressure on the dry density would be best. Using a bentonite which has been investigated extensively over many years means less uncertainty compared to unknown materials.

The oxidation of benzidine to benzidine-blue on silicate minerals is shown to occur at aluminium atoms exposed at crystal edges and at transition metal atoms in the higher valency state present in the silicate lattices. The transition metals in the silicate lattice undergo chemical oxidation-reduction reactions.

Changes in the colour of the benzidine-blue radical cation with the conditions of reaction are discussed in terms of the solvent used for the reaction and its influence on the pH of the mineral surface.