Kaolinite- and halloysite-potassium acetate complexes were synthesized by cogrinding with solid potassium acetate (mechanochemical intercalation). The efficiency of mechanochemical intercalation was compared to the intercalation in solution and by homogenization. The effects of ageing and grinding parameters (grinding time, sample:grinding body mass ratio (SGMR), rotational speed) and the humidity on the intercalation were studied. The degree of intercalation increased exponentially with ageing of the samples prepared by mechanochemical and homogenization techniques. For the mechanochemical and homogenization techniques the required amount of potassium acetate per gram of kaolin (∼0.4 g/g) was two orders of magnitude lower than that for the solution intercalation (78.6 g/g). The highest degree of intercalation (86%) and the lowest structural deformation were achieved by the mechanochemical method (¼ h of co-grinding with 1:2 SGMR at 300 rpm), followed by 16 h ageing at 57% relative humidity.

Dehydration and rehydration of a phlogopitic vermiculite saturated with either Sr2+ or Ba2+ were studied by thermoanalysis (TG, DSC, DTA) and by in situ X-ray powder diffractometry. A detailed analysis of the relationship between temperature and state of hydration of the vermiculites close to equilibrium at atmospheric pressure was rendered possible by use of low heating rates in combination with a fast recording position-sensitive detector. For Sr-vermiculite, the results reveal the existence of a number of distinct states of hydration characterized by basal spacings of 1.54, 1.51, 1.49, 1.23, 1.21 and 0.96 nm. The Ba-vermiculite failed to develop a two-layer hydrate even in contact with water. Its one-layer hydrate (1.24 nm) was reversibly transformed into an incompletely dehydrated ordered ‘mica-structure’ (1.00-0.99 urn), before an irreversibly dehydrated structure was attained at temperatures exceeding 700°C The formation of regular 1:1 interstratification was confirmed for all transformations characterized by a change in the number of water layers. The concluding compilation summarizes basal spacings, stacking orders, layer translations and specific water contents for all discrete states of hydration observed in our experiments at saturation of vermiculite with different alkaline earth cations.

A moderate to high rate of clay sedimentation is characteristic of the Toarcian sequences in the Umbria-Marche basin. The clay mineral assemblages and geochemical characteristics indicate that the Marne di Monte Serrone Formation and the Rosso Ammonitico Umbro-Marchigiano Unit were deposited in a shallow marine environment. In this general palaeogeographic scheme, a reducing subenvironment must have exsisted in which black shale-type facies were deposited resulting in geochemical anomalies in As, Sb, Zn, Co, Cu, Pb, V, Cr, and Ba, among other elements. The high values of both the detrital index and the Ce/Ce* ratio reveal the influence of proximal emerged reliefs. It is suggested that the palaeosoils that developed on the Liassic carbonate Laziale-Abuzzese platform were the source area of these sediments, following a palaeogeographic scheme analogous to that proposed for the Betic Cordilleras (Spain) during the Middle Domerian to Middle Toarcian. The positive and negative Eu anomalies are due to the decisive influence of the weathering process in which sediments with heterogeneous Eu anomaly size were mixed. The final distribution pattern of REE is the result of the different environments to which the clay minerals were subjected and the differences in intensity of weathering.

Zn-exchanged natural clinoptilolite was studied by powder X-ray diffraction and positron annihilation lifetime spectroscopy. The original clinoptilolite tuff was subjected to size fractionation by sedimentation and dissolution of cristobalite (opal-C). After Zn2+-exchange the purified clinoptilolite sample contained 2.2 Zn2+ ions per unit cell. Structural details obtained by Rietveld refinement showed that the Zn2+ cations are located in three sites (Zn1, Zn2 and Zn3) in the channels of the clinoptilolite. Site Zn1 is located in the centre of channel-A (Mg2+-M4 site). Site Zn2 is in channel-B, next to the calcium M2 position. A new Zn3 site is located in channel-A, in imminent proximity to Zn1. Positron Annihilation Lifetime Spectroscopy (PALS) was employed to assess the Zn exchange. As the cation content influences the free volume of the channels, the ionexchange process can be monitored by PALS. The results suggest the existence of two sizes of cavities, in accordance with the structural refinement.

A naturally occurring hematitic iron oxide/layer-silicate complex has been found in red mottled patches of a deeply weathered granite in north-east Scotland. X-ray diffraction shows a basal spacing of 36 Å—also observable by high resolution electron microscopy—which expands to 40 Å with glycerol and contracts to 33·5 Å on heating. Selected area electron diffraction reveals a composite hematite/layer-silicate pattern with the a-axis of hematite parallel to the b-axis of the silicate. The IR spectrum of the complex clearly shows the contribution made by each of the components. The silicate, with bands due to OH stretching at 3602 cm−1, OH deformation at 855 cm−1, and Si-O stretching at 1085, 1035, 540 and 471 cm−1 resembles ferruginous pyrophyllite, while the hematite, with a perpendicular band at 647 cm−1, in-plane bands at 519, 438, 400, 302 and 227 cm−1 and a characteristic pattern of relative band intensities, is similar to a platy form of soil hematite. Electron microprobe analysis of individual particles gives the complex an (Fe + Al): Si ratio of 6:1, which is consistent with a structure made up of twelve octahedral sheets terminated on both sides by a silicate sheet. It seems likely that the complex developed from a siliceous ferrihydrite which became progressively more organized with geological time.

X-ray photoelectron diffraction data for three cleavage surfaces from a crystal of a Norwegian lepidolite containing 2·3% Rb and 3% Mn are reported and interpreted. Rubidium is shown to occupy anhydrous interlayer sites equivalent to those of potassium, and to be distributed uniformly throughout the crystals. Cleavage occurs in Mn-rich regions in which the manganese(II) is located in octahedral sites essentially equivalent to those of lithium. The octahedral Al sites can readily be distinguished from the Li,Mn sites and it is concluded that Al occupies predominantly M(2), cis sites while Li and Mn(II) prefer M(1), trans sites. Photoelectron diffraction data also indicate that 40 ± 5% of the Al is tetrahedrally coordinated, compared with a figure of ∼34% deduced independently from a surface analysis.

Preferred orientation of clay particles in various clay mounts was measured with an X-ray texture diffractometer. Pole distributions are approximately symmetrical about the normal to the sample. Particle orientation is characterized by standard deviations ranging from 7° for thin sedimented layers, to 20° and more for dry-pressed samples, the latter showing less dependence on particle size. The orientation of the reflecting particles may span a considerable angular range affecting the intensities of diffraction peaks observed on contemporary powder diffractometers, even those with moderate axial divergence. A theory based on the diffractometer geometry was developed to calculate the effect of particle orientation. Results are presented as modified Lorentz factors for orientations deduced from experimental observations. In qualitative X-ray diffractometry of clays, preference must be given to preparation techniques which ensure a high degree of preferred orientation and therefore strong enhancement of basal reflections. In quantitative X-ray diffractometry, the main factor is the reproducibility of particle orientation, and suction and dry pressing are promising methods of sample preparation.

The reaction of ammonia with Mg-saturated vermiculite and hydrobiotite was studied by chemical analysis, X-ray diffraction, and differential thermal analysis, and the hydrobiotite also by infrared spectroscopy. The experimental evidence indicates that ammonia is adsorbed mainly as the ammonium ion, formed partly by reaction with interlayer water and partly by reaction with protons dissociated from octahedral layer hydroxyl groups, giving a single sheet of ions and molecules with irregular interlayer spacing. With large flakes (0.5–1.0 mm) the adsorbed ammonia is strongly retained on heating or on rehydration with water vapour: smaller flakes lose ammonia more readily. Ammonia uptake is related quantitatively to cation exchange capacity with two vermiculites and three hydrobiotites, and to the water content prior to adsorption.

Na-saturated vermiculite adsorbs a similar amount of ammonia to the Mg form, but it is mostly desorbed on rehydration. Cu-saturated vermiculite displays intermediate behaviour, with much of the ammonia initially present as a Cu-ammine which slowly reacts to give more ammonium ion.

Sulphur isotope ratio measurements (δ34S) of diagenetic pyrite are commonly used to identify S sources and mechanisms of sulphide formation in basinal sediments. This study reports such data for a diagenetic pyrite nodule from the Brent Group sandstones of the northern North Sea at three sampling scales: 50 cm (core subsample), 500 μm (laser microprobe) and 50 μm (ion microprobe). Similar δ34S variations are found by the laser and ion microprobe techniques. There is a very wide range in δ34S (<−10% to >+50%) within the nodule and isotopically heavy S (δ34S >+20%) is common at all scales. The nodule δ34S distribution does not fit a Rayleigh fractionation pattern. The laser microprobe sampling at 100–500 μm scales seems to be adequate to characterize S isotope variations in this material.

In solutions of three different, stable, Al-Fe(III) hydroxy species, reaction with silica particles for one month decreased the solution pH and gave deposits containing Fe, Al and Si over the surfaces of the particles, joining them together. Infrared difference spectroscopy showed the deposits to be similar to imogolite or feldspathoid phases, depending on the composition of the initial solution. Comparative SEM and EDXA elemental analysis profiles supported the conclusion that these laboratory products were similar to naturally occurring soil cementing agents. An explanation is given for the observed reactions and the formation of materials likely to act as cementing agents in soil.

Halloysite nanotubes (HNTs)/polytetrafluoroethylene (PTFE) nanocomposites were prepared by the cold compression moulding method. The effects of addition of HNTs (HNTs ‘filling’) on the performances of PTFE were explored using X-ray diffraction, Fourier Transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis which showed that HNTs were well dispersed in the PTFE matrix by means of physical mixing at lower contents of 2–5 wt.%; the introduction of HNTs into PTFE could improve the heat stability of the PTFE. Furthermore, the mechanical and tribological performances of the nanocomposites were measured to examine the filling effect. The tensile strength of the HNTs/PTFE nanocomposites at 2–5 wt.% HNTs content increased by ~3.5% while their wear rates decreased by 55–90% relative to pure PTFE, clear proof of the filling effect of HNTs with a high aspect ratio.

Although Thermal Analysis is a useful technique in characterizing the clay constituent of a potentially valuable clay deposit, it is, perhaps, even more useful when the type and amount of non-clay impurities are important factors in its commercial appraisal. The effect of impurities on the physical and chemical properties of the clay may determine its potential uses in bulk, or it may be advisable to remove the impurity, either to improve the grade and quality of the clay or to provide a useful by-product. The application of both qualitative and quantitative thermal data, in the analysis and control of laboratory work in this field, is demonstrated by its use in the assessment of materials such as evaporite-rich clays, siliceous clays, and high-alumina clays.

Sodium smectite clays were enriched with ferric ions (Argel-Fe and Volclay-Fe) to convert the surface charge of the clays from negative to positive and to use the clays in the discolouration of a synthetic effluent composed of seven anionic dyes (mixed from tartrazine, Brilliant Blue FCF and amaranth). The iron content increased from 5.99% to 11.02% for Argel-Fe and from 5.39% to 10.54% for Volclay-Fe. The efficiency of the discolouration of the anion dye mixture was evaluated by measuring the absorbance of the mixture at 562 nm, where the band with the greatest intensity was found. The contact time required for the system to reach equilibrium was ~5 min for both adsorbents. The kinetic adsorption data supported a pseudo-second-order kinetic model. The experimental data support the dual-site Langmuir–Freundlich isotherm model. The maximum adsorption capacities were 88.68 mg g–1 for Argel-Fe and 392.21 mg g–1 for Volclay-Fe. The enrichment of clays with Fe(III) added functionality to the clays and generated adsorbents with rapid adsorption abilities and high discolouration capacities.

Reevesite, the Ni-Fe member of the hydrotalcite group, occurs as a secondary mineral in the serpentinized ultramafic rocks of the Kwangcheon area in Korea, replacing the pecoraitc-magnetite-millerite-polydymite assemblages in small veins lining cracks and fracture zones. Chemical analyses for the reevesites indicate the presence of the Co-analogue of reevesite and the complete solid-solution between Fe3+ and Co3+. The Co-analogue of the reevesite shows the approximate ratio of 3:1 of divalent to trivalent cations, which is in distinct contrast to the comblainite with the ratio of 2:1 reported by Piret & Deliens (1980). The presence of the complete solid-solution phase between Fe3+ and Co3+ is confirmed by synthesis at room temperature. On the basis of the results, the Co-analogue of the reevesite should be named as a new member of the hydrotalcite group, and thereby be distinguished from the comblainite. The partial substitutions of SO2-4 for CO2-3 in the interlayer region might affect the slight increase of the basal spacing in the reevesite. The synthesis performed suggests that the reevesite could be precipitated under either an alkaline or a neutral environment, if carbonate activity is high enough.

The clay fraction of the deposits of the Otjomongwa Pan, southwestern Kalahari, is dominated by Mg-smectite. This mineral formed as an authigenic precipitate in a groundwater-fed lake, without involving the transformation of a precursor mineral. During the earliest recorded period, Mg-smectite formed together with sepiolite and dolomite in a shallow lake. This period was ended by a change in environmental conditions that led to an increase in the depth of the lake and a decrease in salinity and Mg content of the water. This resulted in a transition to a mineral association without sepiolite and including calcite, together with Mg-smectite and dolomite. The depth of the lake gradually decreased after this event, while the lake water progressively became depleted in Mg.

Montmorillonite-water-cation systems were characterized using high-frequency impedance spectroscopy by studying the influence of the solid concentration and the nature of the exchangeable cation (Na+, K+, Ca2+) on the dielectric characteristics of the dispersions. A new method is proposed to calculate the relaxation frequency (fr) and the dispersion factor (α) from a limited number of impedance measurements. By comparison with rheology, microscopy, X-ray diffraction and immersion calorimetry results, it is shown that impedance spectroscopy is a very powerful technique which yields structural information on a complex system. For Na-montmorillonite, two transitions are observed at 2.5% and 3.6% in solids. The cation mobility and the number of connections between particles are described by fr and α, respectively. The two transitions can then be attributed to the formation of the gel and to the reduction of the macroporosity within the gel, respectively. For Ca-montmorillonite, thick layer-stacks form at the lowest concentrations, and connections between these stacks are observed at 9% in solids, in good aggrement with rheological measurements. The K-montmorillonite displays progressive thickening of the tactoids, and no formation of a unique connected network, as revealed by the smooth evolution of fr and α.

The diagenetic history of an interbedded sequence of Middle Jurassic Sleipner (or Pentland), Hugin and Heather Formation sandstones and mudrocks from the Brae Area has been investigated using petrographic, stable isotope, fluid inclusion and K-Ar dating techniques. Generally, similar diagenetic processes affected both the mudrocks and sandstones resulting in the formation of carbonate, quartz and clay cements and evidence of dissolution and secondary porosity except for the absence of kaolinite in the Hugin Formation. The mudrocks were possible sources of some components involved in sandstone diagenesis but were not passive exporters of such reactants as similar reactions also occurred in the mudrocks. The stable isotope data indicate that most of the diagenetic processes occurred in the presence of marine or evolved marine pore-waters.