The <2 µm fraction from the eluvial horizon of a humus-iron podzol is composed predominantly of a dioctahedral mineral with a basal spacing of 14.7 Å which contracts to 13.7 Å on solvation with glycol, and to 11.4 Å on heating to 300°C. The interlayer region is partially filled with an amorphous organo-Fe-Al complex which is very unstable and is affected by every treatment employed, even homoionic cation saturation. The mineral has a mica-like morphology, contains 3.4% non-exchangeable K2O and is considered to be an interstratified mica-vermiculite formed by the weathering of mica. The contraction of the basal spacing with glycol is probably due to water being removed from the interlayer region of the vermiculite component, leaving only the natural organo-complex in the interlayer; alternatively, the contraction may be more apparent than real, resulting from an interstratification effect. Treatment with H2O2 results in partial expansion with glycol.

Goethite is an important component of many soils and its transformation to hematite by fire may affect phosphate retention. This study deals with the kinetics of phosphate sorption and desorption by synthetic aluminous goethites and their dehydroxylated products. Phosphate sorption and subsequent desorption were measured for periods up to 128 h. Phosphate sorption increased with equilibrium solution concentration, Al substitution and surface area, and decreased with increasing crystal size. The trend in amount of phosphate sorbed was: partially dehydroxylated goethite > hematite > goethite. Sorption and desorption kinetics are well described by the modified Elovich equation. Desorption of a minor proportion of the sorbed P was rapid and this was sometimes followed by minor resorption. The amount of P desorbed directly reflected the amount that was initially sorbed. Acid dissolution of the Fe oxides with sorbed phosphate suggested that most phosphate was present at the crystal surface and not in relatively poorly accessible micropores.

The weathering of montmorillonite in the acid clay deposit at Itoigawa, Japan has been investigated by X-ray diffraction (XRD), infrared spectroscopy (IR) and scanning electron microscopy (SEM). In the lower, least weathered part of the deposit, weathering has occurred by the formation of minor amounts of halloysite with concomitant precipitation of a silica phase identified as opal C-T. A relatively rapid transition occurs to the most weathered, upper part of the deposit where the mineralogy is dominated by interstratified halloysite-smectite. Computer simulations of XRD profiles indicate that the interstratified arrangement is random with a probable composition of 70% halloysite and 30% smectite, a composition supported by the 75–85% and 15–25% of the phases, respectively, calculated from the IR spectra.

Interactions of ammonium sulphates and various silicate and oxide minerals have been studied by X-ray heating methods and simultaneous TG-DTA. Kaolinite and other clay minerals were found to be very susceptible to these sulphating treatments, (NH4)3Al(SO4)3, (NH4)Al(SO4)2 and Al2(SO4)3 being formed successively with increasing temperature from 350 to ∼550°C. The same reaction products were obtained on heating mixtures of (NH4)2SO4 and γ-Al2O3, Al(OH)3 and bauxite. Fe-, Mg- and Ti-silicates and oxides gave NH4-double sulphates below 400°C and the corresponding metal sulphates above this temperature.

The strongly coloured Cu-triethylenetetramine complex (Cu-Trien) provides a fast and easy way to measure the cation exchange capacity of clay samples, but the reliability of this method has been questioned in recent publications. This work identifies several reasons for the poor reliability, thus improving both the precision and accuracy of the CEC method. Pure Trien is shown here to intercalate as does the Cu-Trien complex. Hence, the purity of Trien and also the Cu/Trien ratio require special attention. Using cold Cu-Trien solutions produces systematic deviations in CEC determinations caused by errors in the pipetted volumes. The present study demonstrates, for the first time, that the Cu-Trien complex protonates and changes its effective charge beyond 2+. Based on titration experiments at three different temperatures, a correction function is derived for calculating the total charge of the Cu-Trien complex as a function of pH. Accounting for these pH-corrected charges indicates that Cu-Trien may well be insensitive to edge charges on smectite. Finally, it is shown here that the ratio of sample mass to the initial amount of Cu-Trien is critical because excess adsorption of Cu-Trien in addition to CEC sensu strictu was observed.

Measurement of clay particle size invariably presents data in the form of equivalent spherical diameters. For asymmetric particles the equivalent spherical diameter varies with the method of measurement. Based upon an understanding of the theoretical concepts involved, a method has been proposed whereby comparison of data on a given sample from two different techniques can reveal information about the minor dimension of the particle. Theoretical expressions are given for the equivalent spherical diameter of cylindrically symmetric rods and discs from which it is shown that some of the existing measurement methods are more dependent upon size than the degree of non-sphericity whilst for others the reverse is true. It is shown how for rods and discs one can obtain information on both an average axial ratio and the distribution of this parameter for heterogeneous samples. Illustrated data are given for three kaolin samples. Far from showing inconsistency between the variable spherical diameters yielded by different instruments, the data produce compatible size and thickness parameters which match those observed in supplementary, unreported electron microscope experiments. A method of measuring particle major and minor parameter distributions is indicated.

The development of the infrared (IR) absorption band at 1640 cm−1 (δH2O) is employed to monitor the gain in molecular water of progressively mortar-ground kaolinite. The planimetred area of this band shows a linear correlation with weight loss at 105°C (free moisture) between 2 and 18 h grinding, indicating a steady increase of molecular water in this range. Heating of ground products to 105°C causes a decrease of about ⅓ in the 1640 cm−1 peak area for all ground samples. This area decrease corresponds to a 34% (average) loss of free moisture as determined by gravimetry. The remaining water is held up to 280°C and is more tightly held in the kaolinite ground for shorter (2–5 h) intervals than in further ground kaolinites. The 1640 cm−1 peak is not detected in any ground kaolinite after heating to 600°C the temperature at which kaolinite dehydroxylates completely. The differentiation of the energetically different OH groups present in ground kaolinite and the mechanism of water gain are compared and discussed from IR spectroscopy and weight loss results.

Three clay minerals from southern and central Tunisia were characterized. Both XRD quantitative analysis and a chemical method were used to determine the mineralogical and physico-chemical characteristics of the <2 μm clay fractions. The XRD, CEC and specific surface measurement analyses showed that the dominant phase in all samples is illite-smectite with kaolinite and traces of quartz also present. From quantitative XRD, the abundances of the minerals identified are consistent with the measured CEC, specific surface area and TG/DTA properties. Analysis by XRD also showed that the illite-smectite phases are composed of thin stacks (two to a maximum of ten layers per stack) of random illite-smectite and ordered (R1) illite-smectite. There is also some discrete illite.

The diagenesis of illite from smectite was investigated in relation to temperature on marly shale core samples from different Tertiary stages (depths between 200 and 3000 m) by X-ray and chemical analyses. It is concluded that the alteration of smectite to illite primarily depends on the cumulative energy supply (temperature × time). Small grain size and high potassium concentrations in the pore solutions shorten the time necessary to complete the alteration. Potassium is supplied by decomposition of feldspar within the sediment so that the replacement of feldspar by secondary calcite increases the availability of potassium. Supply of potassium by pore solutions from distant sources is very unlikely due to reduced permeability in compacted shales. Illite diagenesis is influenced by the inherited layer charge of the initial smectite.

Tannic acid-stabilized silver nanoparticles were synthesized in situ on halloysite clay nanotubes. The synthesis strategy included simple steps of tannic acid adsorption on clay nanotubes and further particle formation from silver salt solution. Pristine halloysite nanotubes as well as amino-modified clays were used for silver stabilization in water or ethanol. The materials were tested for antibacterial performance using three different methods. All of the materials produced showed antimicrobial activity. The pristine halloysite-based material with ~5 nm particles produced using ethanol as the solvent and tannic acid as the reducing agent showed the greatest antibacterial activity against Serratia marcescens. The materials were tested in vivo on Caenorhabditis elegans nematodes to ensure their safety, and they showed no negative effects on nematode growth and life expectancy.

The origin and distribution of late Maastrichtian–early Palaeocene clay mineral associations were investigated in the Tremp-Graus basin (South Pyrenees, Spain) to assess palaeoclimate changes during that period. The studied succession is made up of expanded continental and transitional terrigeneous and carbonate deposits accumulated in a coastal plain setting. X-ray diffraction, SEM-EDX and TEM-AEM analysis reveal that the main clay components are illite and smectite, but kaolinite, chlorite and illite-smectite mixed layers are present, although irregularly distributed, all of them showing a platy morphology typical of a detrital origin. Persistence of the chemical features of the Al-dioctahedral smectites throughout the whole succession demonstrates the persistence of the same source area during the interval studied. Palygorskite occurs in the late Danian and Selandian, within carbonate tidal flats as sabkha-like facies. In SEM images, the palygorskite displays straight fibre morphologies, both coating and branched curling out, a clear proof of authigenic origin.

Physical or chemical weathering (PhW/ChW) determined as illite + chlorite/smectite + kaolinite ratio, smectite/kaolinite ratio and palygorskite distribution have been used as clay proxies for palaeoclimate reconstructions. Such data suggest a shift from temperate subhumid (perennial) conditions in late Maastrichtian times to a warm seasonal climate during early Palaeocene times. This trend, however, was dramatically altered during the late Danian–Selandian interval, when prevailing warm and semi-arid to arid climatic conditions caused intense evaporation and the development of an alkaline environment in which the palygorskite authigenesis took place.

The proposed climatic trend partly concurs with that established for earliest Danian time by Domingo et al. (2007), also in the Tremp-Graus basin, from isotopic and geochemical proxies, as well as with the reconstruction of Cojan & Moreau (2006), in which a semiarid Danian phase for the near continental basin of Aix-en-Provence is postulated. However, it is at odds with the notion of a humid Danian state in the Pyrenees, as inferred by Gawenda et al. (1999) from clay mineral proxies of deep marine successions.

The main clay mineral in weathered basaltic rubble has been shown by X-ray diffraction, chemical, infrared and differential thermal methods to be an interstratification of montmorillonite, vermiculite and illite in the approximate ratio 2:1:1, the montmorillonite having some degree of segregation and the vermiculite and illite being randomly interstratified. All three components are dioctahedral, the swelling ones having a high tetrahedral charge, a large aluminium content, and very little iron. Despite the 50% montmorillonite content of the mineral, its infrared absorption pattern is generally illitic in character.

Characterization of platiness of kaolin pigments was derived from the divergence of measurements of their particle size distribution by two different techniques: sedimentation and light scattering. A numerical shape factor, which is related to the ratio of kaolin particle face diameter to its thickness, can be calculated to provide a quantitative measure of such platiness. Two sets of kaolin pigments were prepared from a Middle Georgia kaolin: delaminated and non-delaminated. Shape factors of delaminated samples were higher than those of non-delaminated ones. Maximum platiness was found between equivalent volume diameters of 1·0 and 2·0 μm. Examples are presented where properties of coated paper are correlated with the size and shape of kaolin pigments.

Sediments of the Tertiary Akata and Agbada Formations have been studied by mineralogical and petrographic techniques. In the Akata and Agbada shales the clays are largely detrital, with only minimal alteration attributable to the effects of burial diagenesis. Clay minerals occur in minor (<10%) amounts in the reservoir sandstones of the Agbada Formation both as detrital and authigenic phases. There are significant differences between the clay assemblages of the water- and hydrocarbon-bearing sandstones. The latter have lower overall clay contents and authigenic kaolinite, whilst authigenic kaolinite and smectite are present in the water-saturated sandstones. These differences are thought to be related to the early migration of hydrocarbons into the reservoir sands. The causes of the poor degree of cementation in the Agbada sandstones are discussed along with the engineering problems posed by their very friable nature.

The adsorption of organic ions derived from ammonium, containing aromatic and saturated rings, was studied using different techniques. The ions with acid character produced a complicated set of reactions including aluminium extraction, proton adsorption, a real ion-exchange with the organic ions and an excess adsorption of ammonium salts. With non-acidic compounds only a stoichiometric ion-exchange process was observed. X-ray diffraction and infrared spectroscopy were used to determine the orientation of the organic ions and to characterize the nature of the co-adsorbed organic material.

The small particle size and the random stacking of layers has previously hindered systematic structure investigations of montmorillonite. By applying the convergent-beam electron diffraction mode (CBED) of a transmission electron microscope (TEM) with a beam spot of ~800 Å we were able to examine undisturbed areas of montmorillonite crystallites.

Because montmorillonite crystallites are mostly thin particles, kinematic theory can be applied and the CBED patterns can be interpreted directly, provided that the particle thickness remains below the critical value of 350 Å. An average thickness of ~90 Å was calculated here for montmorillonite of bulk samples from X-ray diffraction analysis and lattice-fringe images. However, satisfactory diffraction intensity patterns for quantitative evaluation were obtained only from crystallites with a thickness above the average, which yielded a sufficient scattering volume. These patterns could be described in terms of the kinematic theory and therefore these crystallites were <350 Å thick. Yet, crystallites of adequate thickness were extremely rare in the three samples investigated (Clay Spur, Rock River and Upton, all in Wyoming, USA).

The diffraction intensities from the ab plane of single montmorillonite crystallites of the various origins fit the three structural models for a trans-vacancy distribution, a cis-vacancy distribution or a random-cation distribution within the octahedral sheets. The configuration of the diffraction patterns also shows a 1M symmetry of the layer. Due to the limited data set of CBED patterns, a refinement of the structure could not be achieved. However, energy dispersive X-ray spectroscopy data and computation of the cation–anion distances and valences using the ‘distance valence least square’ program permitted a refinement of the models.

Hydrothermal alteration of Proterozoic granitic rocks in the Äspö underground laboratory, southestern Sweden, resulted in the formation of chlorite with large variations in textural and chemical characteristics, which reflect differences in formation temperatures, fluid composition, and reaction mechanisms. The mineral assemblage associated with chlorite, including Ca-Al silicates (prehnite, pumpellyite, epidote, and titanite), Fe-oxides, calcite, albite and K-feldspar, suggests that chloritization occurred at temperatures of between 200–350°C during various hydrothermal events primarily linked to magmatism and rock deformation. Petrographic and electron microprobe analyses revealed that chlorite replaced biotite, amphibole and magnetite, and hydrothermal chlorite phases filled fractures and vugs in the granitic rocks. While fracture-filling chlorite reduces fracture permeability, chloritization reactions in the host granite resulted in the formation of new localized microporosity that should thus be taken into consideration when evaluating the safety of the granitic basement rocks as a repository for nuclear waste. It is also important to take into account that similar alteration reactions may occur at the site of stored nuclear waste where temperatures in excess of 100°C might be encountered.

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.

An important attribute for soil use is clay content, because it affects the water-holding capacity and hydraulic properties of a soil. Soil surveys are time-consuming, labour-intensive and costly, while geophysical methods, such as Electromagnetic Induction (EMI) and Ground Penetrating Radar (GPR), offer a non-invasive and non-destructive approach to mapping soil features. The objective of this paper is to assess the spatial relationship between clay content and geophysical data. The EMI and GPR data and soil cores were collected and analysed in a field of about 3 ha size in Rutigliano, Bari, in SE Italy. The EMI data and clay contents were interpolated using ordinary cokriging. The GPR data were pre-processed and the envelope of the filtered GPR data was used to produce 3Dmaps of the kriged estimates. The correlation with clay content was large and positive for EMI, whereas it was negative for the GPR measurement. In this work, a combination of geostatistical and statistical analysis has shown a significant correlation between the EMI and GPR observations. Estimation of the mathematical function relating these two groups of variables requires a multivariate approach of non-stationary geostatistics.

The Etive Formation of the Middle Jurassic Brent Group in part of the Northern North Sea comprises dominantly clean, fine- to medium-grained sands, deposited as part of a barrier-bar complex. The overlying Ness Formation was deposited on supra- or intertidal fiats, and comprises silty channel sands with silts, muds and thin coals. The sands of both Formations are mainly quartz-rich, with up to 12% by volume of feldspar, and variable proportions of clayey matrix. Early carbonate cementation preceded a phase of quartz overgrowth, which continued during burial. Later dissolution of unstable grains, dominantly feldspars, was followed by precipitation of pore-filling kaolinite and minor late-stage mineral phases. Better permeability of the Ness sands (up to 500 mD) relative to the Etive (mostly <10 mD) is mainly due to the effects of diagenesis on different lithofacies. Silty sands escaped intense quartz cementation and were thus more affected by acid groundwaters which improved permeability.