Chlorites from Cambrian basaltic vesicular lavas, characterized by relatively high Xc (0.81-0.98), gave temperatures of formation of 285 to 350°C (Cathelineau's empirical geothermometer). Both the Xc and temperature calculations gave results which were too high for the diagenetic conditions indicated by the interbedded shale mineralogy. The HRTEM and XRD studies indicate the absence of smectite layers in these chlorites; i.e. according to lattice images, the actual value of Xc is 1. The chlorite composition in these basaltic lavas must, therefore, be explained in relation to their whole-rock geochemistry, with which a good correlation has been found. The basaltic lavas are characterized by relatively high FeO/M ratios (3.28±1.66) and must be considered as an Fe-rich system, with similar chemical behaviour to pelitic rocks. In these cases, direct chlorite formation, without a previous smectite precursor, is a normal occurrence and the Xc calculation and empirical geothermometric calculations are inadequate.

Self-diffusion coefficients of water molecules (1H2O) in Na-stevensite gel were measured by pulsed-gradient spin-echo (PGSE) proton nuclear magnetic resonance (NMR). The effects of clay fraction (0.00 37.7 wt.%) and temperature (20.0 60.3°C) were studied. The results show: (1) phenomenologically, the H2O self-diffusivity in the clay gel, D, is expressed by D/D0 = exp( 0.0198w) where D0 is the H2O self-diffusivity in bulk water of the temperature and wis the clay weight fraction (wt.%). (2) The activation energy of the diffusivity in the stevensite gel is nearly equal to that in bulk water. Thus, the normalized diffusivity, D/D0, obeys a temperature-independent master curve. (3) The exponential dependence of D/D0 on wfor w <25 wt.% (≈ 12 vol.%) can be explained by a random walk model, in which unbound H2O molecules diffuse in the geometrically tortuous pore structure of randomly scattered clay mineral grains. (4) The measured diffusivity can also be explained by a model of unbound H2O diffusing in a polymer network with a specific meshsize or characteristic interval of the crosslinkage.

The morphological and structural changes in smectite caused by hexadecyltrimethylammonium (HDTMA) treatment were studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The HDTMA-exchanged smectite shows not only morphological features such as irregular, wavy surface with curled edges, but also structural features such as large d-spacings (20 – 26 Å ) and lattice distortions. The surface morphological heterogeneity is assumed to be related to the inhomogeneous intercalation of HDTMA cations into the interlayer of smectite.

Analysis of the near-infrared (NIR) spectral bands of phyllosilicates, together with the mid-infrared bands, enables testing and confirmation of band assignments for the structural OH vibrations. Spectral analyses of selected smectites and serpentine-kaolin minerals are presented here. The results of this study indicate that dioctahedral smectites may contain both in-plane and out-of-plane OH-bending vibrations, as suggested by Farmer (1974). In-plane bands occur near 800 ­ 915 cm–1, while the weaker out-of-plane vibrations occur near 600 ­ 700 cm–1 and are enhanced in dioctahedral smectites when the structure is disrupted by substitutions. Analysis of the OH-stretching vibrations and their NIR overtone bands is also presented for both smectites and serpentine-kaolin minerals. These overtones are more straightforward for serpentines than for kaolinite, and a strong overtone associated with the kaolinite OH-stretching band at 3620 cm–1 is found that supports its assignment as an OH-stretching band.

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.

Three steps have been established during the Holocene formation of the bar-built estuary of Las Nuevas (Doñana National Park, Spain), on the basis of the clay mineralogy variations and the palaeontological record. The first step is characterized by the presence of ostracodes and homogeneous quantities of clay minerals (17–20% illite, 25–29% smectites), values of smectite (0.64–0.70) and illite (0.60–0.70) crystallinity indexes, and the ratio of AlVI/(FeVI + MgVI) in illite (0.46–0.47). This zone is interpreted as a very shallow lagoon with euryhaline conditions. The presence of roots, the progressive disappearance of foraminifers and an increase in the smectite content (up to 35%) define the second step. A salt-marsh environment with low-energy hydrodynamic conditions is deduced for this zone. The third step is characterized by an increase in illite content (up to 35%), and a decrease of the smectite content (up to 21%). The smectite crystallinity index decreased to 0.38, whereas the illite ratio AlVI/(FeVI + MgVI) decreased to 0.36. In this zone, the ostracode assemblage contains numerous juvenile stages of coastal species coinciding with lumachelle accumulations of the estuarine bivalves, abundant foraminifers and the presence of charophytes. This zone represents a strong marine input, probably caused by storms.

X-ray powder diffraction patterns were simulated for nano-sized hematite, goethite and lepidocrocite by three-dimensional integration in reciprocal space. The cell-edge lengths were refined together with the size parameters X and Xe of the Thompson-Cox-Hastings function, which for orthorhombic structures was extended by a biaxial broadening parameter Xo. Variations of the structure factors across broad peaks resulted in apparent peak shifts and concomitant shifts in celledge lengths, which were significantly correlated with the size parameters for hematite and partially correlated for goethite and lepidocrocite. Regression equations are given for correcting cell-edge lengths obtained from Rietveld fits for size-induced shifts.

Six smectites of different tetrahedral and octahedral compositions (SAz-1, Chambers, Belle Fourche, two subsamples of nontronite 33B and SWy-1) were Cs-exchanged and submitted to 70 wetting-and-drying cycles. X-ray diffraction (XRD) of oriented and glycolated mounts of the resultant material showed non-expandable layer proportions ranging from 15 to 60%. They were also analysed by powder XRD at 200°C in vacuum. These patterns showed that 15 – 40% of the layers were not rotated relative to each other and the rest were randomly rotated (no rotations of the 60° and 120° types). All layers had a d-spacing of 11 Å, corresponding to collapsed layers with Cs in the cavities created by the hexagonal rings of the tetrahedral sheets. Analysis of the number of cavities available in relation to the layer rotation shows that the rotation angle must be close to 30° or its multiples 90, 150, 210, 270 and 330°. X-ray diffraction and thermal analysis detected the same proportion of cis-and trans-vacant sites in the smectites. The ideal bdimensions of the tetrahedral and octahedral sheets (the sheets are considered independently, without deformation) were calculated for the samples used in this work and for others from the literature, using the tetrahedral and octahedral compositions. These ideal bdimensions have a strong positive correlation. The cis/transvacant character of the smectites is related to the relative lateral dimensions of the ideal tetrahedral and octahedral sheets. A possible explanation of this fact is offered, in which the different configurations of hydroxyls and oxide ions in cis- and trans-vacant structures can affect octahedralsheet dimension.

A new method is proposed for modelling complex X-ray diffraction patterns effectively. The method is based on the calculation of the interference function of the onedimensional disordered crystals with finite thickness. First, we calculated the diffraction effects from structures of individual mineral phases with different layer defects modelled according to the Reynolds’ algorithm. To fit the theoretical to the observed XRD patterns more accurately, we then used a specially developed optimization procedure. This iterative procedure selects the optimal set of chemical and structural parameters (probability and domain size) and yields consistent solutions.

The composition of the clay component in bottom sediments of Lake Baikal relates strongly to glacial/interglacial climate cyclicity. Besides changes in the relative abundance of illite and illite/ smectites between glacial and interglacial periods, significant differences are observed in the crystal chemistries and structures of layered minerals. A change from chlorite during glacial periods to chlorite-smectite during interglacials is probably indicative of the weathering processes in the watershed. Changes in the degree of ordering, in domain size and grain-size distribution of illitesmectites imply differences in genesis of this mineral phase in different palaeoenvironments. These findings further strengthen the case for using clay minerals in the sedimentary record of Lake Baikal as palaeoclimate indicators.

One of our findings was that none of the fractions separated by Stokes’ settling is representative of the bulk sample for either the glacial or interglacial intervals. For the interglacial sample, illitesmectite was concentrated in the <2 μm fraction whereas, for the glacial sample, most of illitesmectite is contained in the <1 μm fraction. The selective use of one fraction is yet another potential source of uncontrolled errors that has to be avoided. We suggest using X-ray patterns of bulk samples as a preferred method of analysis of Lake Baikal (and other) sediments.

Opaline silica residue accumulates on the surface and in the near surface of the Te Kopia, Tikitere and Rotokawa geothermal fields, where rhyolitic tuffs are attacked by steam condensate, made acid (pH 2–3) by sulphuric acid produced by oxidation of H2S that accompanies steam discharge. Silica residue is one product of this alteration process that also yields kaolinite, sulphur, sulphide and aluminous sulphates, including alunite and alunogen, as pH, Eh and available moisture fluctuate across the field surface. Coagulation of colloidal polymeric silica or, possibly, direct deposition of monomeric silica can occur from the acid solutions of the digested country rock, depending on pH, concentration, temperature and the presence and concentration of other species. As with silica sinter, the first-formed silica phase consists of disordered opal-A microspheroids, commonly 0.1–5 μm in diameter. These coalesce and become overgrown by further opaline silica to yield a mass resembling gelatinous ‘frog spawn’ that lines cavities and envelops surfaces. This mass is the principle component of botryoidal, transparent to translucent hyalite that comprises much residue. Following deposition, this juvenile residue may crystallize to opal-CT lepispheres, 1–3 μm across and, subsequently, to chalcedonic quartz. Both the opal-A and opal-CT of the New Zealand residues are more disordered than those occurring in typical moderate- to low-temperature sinters. The opaline silica of silica residues enjoys a reaction relationship with both kaolinite and aluminium sulphates, including alunite and alunogen. These phases and the silica precipitate continuously and undergo dissolution at the surface of all three localities. The precise pathway followed depends upon the prevailing surface conditions, including humidity, pH, Eh, and Al and K activities. As Al is flushed from the system, the ultimate stage of alteration that may result is the dissolution of the silica itself in acidified rainwater, fogdrip or further steam condensate.

X-ray powder diffraction patterns of halloysite (7 Å) are characteristically altered following solvation with ethylene glycol. Some effect was first noted in the classic work of MacEwan but its value in the unequivocal identification of halloysite (7 Å ) seems to have been overlooked subsequently. The response to ethylene glycol solvation involves a decrease in the intensity (peak height) of the peak at ∼7.2 Å and an increase in the intensity (peak height) of the peak at ∼3.58 Å thus narrowing the 7.2 Å /3.58 Å peak height intensity ratio. For pure samples of halloysite, this ratio is narrowed by an average of ∼50%. This distinctive change is related to the interstratified nature of halloysite (7 Å), specifically the presence of ‘residual’ interlayer water, i.e. halloysite (10 Å), which can be replaced with ethylene glycol so forming 10.9 Å layers, a spacing that is almost exactly one and a half times the thickness of dehydrated (7.2 Å) layers which do not imbibe ethylene glycol. Thus the separation between the 001 peaks in the 7.2 Å /10.9 Å interstratification is increased and the 0027.2 (3.58 Å) and 00310.9 (3.63 Å) peaks become more or less coincident, compared to the 7.2 Å /10 Å interstratification, i.e. the partially hydrated state. The widespread use of ethylene glycol solvation in clay mineral studies makes it a particularly useful and simple test to determine the presence of halloysite. Pure halloysites should be readily identifiable and experiments indicate a ‘routine’ sensitivity of ∼20% halloysite in mixtures with kaolinite, although this will depend on factors such as ‘crystallinity’ and could be improved with careful attention to intensity measurements. It is proposed to call this phenomenon the ‘MacEwan effect’ in honour of its discoverer Douglas Maclean Clark MacEwan.

The crystal-chemical mechanisms by which transition metals are associated with goethite are fundamental to our understanding of the solubility and bioavailability of micronutrients and heavy metals in soils, and in the formation of laterite ore deposits. Transition metals such as Cr, Mn and Ni may sorb onto goethite by forming surface precipitates, surface complexes or by replacing Fe3+ in the goethite structure. In the work reported here, we investigated the local coordination environment of Cr, Mn and Ni in synthetic goethite using EXAFS spectroscopy. We demonstrate the isomorphous substitution for Fe3+ by Cr3+ (up to 8 mol.%), Mn3+ (up to 15 mol.%) and Ni2+ (up to 5 mol.%). We find, however, that the next-nearest-neighbour coordination environment changes with composition. The perturbations are likely to be responsible for limiting the accommodation of Cr3+, Mn3+ or Ni2+ in the FeOOH structure.

Tritium accumulation in clay minerals (kaolinite, montmorillonite, palygorskite) was studied experimentally over a one year contact with tritiated water (initial activity 1.676x109 Bq/m3) under room conditions, and was compared to theoretical calculations. The amounts of tritium ions in bound water and structural hydroxyls were measured by the activity of water fractions released at characteristic temperatures determined on the basis of the mineral DTA patterns. Experiments showed that after a 400 day contact with tritiated water, tritium exchange rates (θ) were highest in palygorskite (θa = 0.42 in bound water and θs = 0.51 in the structure) compared to montmorillonite (θa = 0.15 and θs = 0.11, respectively) and kaolinite (θa = 0.34 and θs = 0.02, respectively). This could be due to different tritium concentrations in the solution near the bound-water layers, and also to certain features of the mineral structures, most of the kaolinite structural hydroxyls not interacting directly with bound HTO molecules.

Tritium accumulation in these minerals, under room conditions, can be described by a relatively simple two-stage isotope exchange model in which tritium ions first migrate from the solution to the bound layers and then substitute the protons of the structural hydroxyls. Rate constants for both stages of this isotope exchange were calculated on the basis of the experimental data.

Theories concerning the optical properties of cationic dyes adsorbed on clay surfaces are analysed in detail. An investigation of the aggregation of methylene blue (MB) in montmorillonite dispersions is conducted using visible (VIS) spectroscopy. The effects of the dye/ clay ratio and of the swelling properties of the montmorillonite substrate on dye aggregation are compared in terms of the effect of clay layer charge. The observed influence on dye aggregation was almost negligible for both swelling and dye loading. The layer charge of the silicate determines the extent and the type of dye aggregation in freshly prepared MB/montmorillonite dispersions. Observed spectral changes with time indicate a rearrangement and redistribution of dye H-aggregates (band close to 570 nm) to monomers (660 nm), dimers (605 nm) and J-aggregates (760 nm). Dye aggregates are probably already formed during dye cation migration in the vicinity of clay colloid particles. The extent and the type of initially formed species are probably affected by the electric double layer of clay layers. After reaching the clay surface, dye cation assemblies are rearranged and decompose as described above. Reaching chemical equilibrium, dye cations adjust the distribution of the layer charge, in order that each cation could balance the charge due to one unequivalent substitution.

A natural phengite-2M1 of composition (K0.95Na0.05)(Al0.76Fe0.14Mg0.10)2 (Si3.25Al0.75)O10(OH1.96F0.04) [a= 5.2173(1) Å, b= 9.0493(2) Å, c= 19.989 (1) Å and β = 95.734(4)°] was studied using in situ high-temperature FTIR. Correlations to structural changes were made using previously-reported neutron diffraction data from the same sample. Correlations have been made between the microscopic atomic displacements (arising from thermal effects) and analogous macroscopic properties, such as bond strain and ditrigonal distortions. Spectra were collected in the far-infrared region to study the behaviour of the interlayer (K+) cation and also in the mid-infrared region to distinguish the Si–O stretching modes. We found anisotropic thermal expansion of the interlayer site. The K O bond length is divided into K Oouter and K Oinner, and the K–Oinner bond length is correlated with the far-infrared spectra. The thermal dependence of the correlation between K–O bond length and corresponding far-infrared stretching frequency is different from the effect of the chemical composition. We also found that the K–O bond strain could be successfully resolved into the sum of inner strain and lattice strain. The Si–O stretching mode, obtained from the mid-infrared measurements, showed only weak changes. However, the neutron refinement data showed different thermal behaviour for distinct crystallographic T-sites.

Some soils from the western Amazon region contain KCl-extractable Al contents 5 to 10 times greater than is typical for highly weathered soils containing predominantly kaolinite and gibbsite. We studied a soil sequence from the Brazilian western Amazon consisting of two Typic Udifluvents on the levee of the Javari River, one Aeric Endoaquent in the backswamp, and two Typic Hapludults on an adjacent terrace. We used wet chemical and X-ray diffraction (XRD) analysis to characterize several size fractions of the 0 to 0.2 m layer of the soils. The exchangeable Al content was very high in the Aquent and Udults (up to 180 mmolc kg–1), but the ‘total’ Fe content was low in all samples (<60 g kg–1). Smectite, vermiculite, hydroxy-interlayered smectite and kaolinite dominate the fine silt and clay fractions of all soils. The Fluvents contain illite in all size fractions and chlorite in the coarse clay and fine silt fractions. The Aquent and Udults have no chlorite, and small amounts of illite occur only in the coarse clay and fine silt fractions. Lepidocrocite was identified in the Aquent. Chlorite, which occurs in the sand, fine silt, and coarse clay fractions of the Fluvents, and pyrophyllite, which occurs in the fine silt fractions of all soils and in the coarse clay of the two Ultisols, appears to be inherited from the parent sediments. The hydroxy-interlayered 2:1 phyllosilicates that form as a result of weathering are the cause of the very high exchangeable Al contents.

The synthesis of clay composites modified with magnetite and Co ferrite magnetic nanoparticles is described. The synthetic method relies on the adsorption of colloidal magnetite or Co ferrite particles onto the external surfaces of a Na-saturated clay mineral to give magnetic clay composites that can be converted easily, through ion exchange reactions, to valuable clay derivatives, e.g. organoclays, which maintain the magnetic properties of the parent composite. The magnetic solids were characterized by XRD, EPR, Mössbauer, magnetic measurement and TEM techniques.

Competitive adsorption of glyphosate and phosphate on goethite and gibbsite and on illite, montmorillonite and two kaolinites differing in surface area was evaluated. The results show that glyphosate and phosphate are competing for the adsorption sites, but the degree of competition depends on the adsorbent. On goethite the competition is very much in favour of phosphate, on gibbsite the competition is closer, but still phosphate is favoured, while on illite, montmorillonite and kaolinite the competition is almost equal. The amounts of glyphosate and phosphate, which can be adsorbed also depends on the adsorbent: the oxides adsorb more than the clay silicates. The amount adsorbed on kaolinite was dependent on the specific surface area. Changes in the surface area did not affect the competition between glyphosate and phosphate for adsorption sites. The results indicate that differences among soils of different mineralogical composition regarding the adsorption of glyphosate and phosphate can be expected.

Three soil profiles classed as brown forest soils on schistose parent material, in close proximity but under different land uses, have been studied. The profile under 50 year-old Sitka spruce trees is the most acidic, the second profile under rough grassland is less acidic, and the third profile in an arable field which has been fertilized is the least acidic. The clay fractions (ς μm) of all three profiles are very similar. However, computer simulations of the X-ray diffraction patterns of clay phases using a modified version of NEWMOD revealed two possible weathering trends: (1) an increasing proportion of vermiculite in interstratified mica-vermiculite in the upper horizons of the arable and forested soils; (2) formation of high-charge corrensite by weathering of chlorite in all three profiles but least pronounced in the arable soil. The differences in clay mineralogy amongst the profiles are minor, but these two different weathering trends may be due to the effects of different land use.

Bentonite samples from Choushan treated at various acid concentrations were studied using chemical analysis, XRD, 29Si and 27Al MAS NMR to investigate the microstructure of the activated montmorillonites. Two types of structural units were formed during the activation: (1) (SiO)3SiOH, in which up to 15% of Si is bound; (2) Q4(0Al), a major building unit when the acid concentration is >10%. A significant 27Al signal at 55.0 ppm was recorded for both untreated montmorillonite and (to a much greater extent) in acid-treated montmorillonites. This was interpreted as arising from four-fold coordinated Al located in the ‘bulk’ octahedral sheet of montmorillonite. In the course of activation, the removal of one of a pair of octahedral Al ions from montmorillonite removes two hydroxyl groups and leaves the other Al of the pair in four-fold coordination.