A naturally occurring macroscopic sodium vermiculite from Unst, Shetland is described. It is similar in many respects to synthetic materials recently prepared from phlogopite by potassium replacement. In other respects, however, it is more akin to macroscopic Mg-vermiculites.

A series of thin clayey beds topping shallow marine cyclothems was sampled from a Turonian succession in Israel and was analysed by XRD for the mineralogical composition of its clay fraction. The main goal was to search for potential relations between short-term shallowing and possible emergence events and clay mineralogy. The bulk (<2 μm), coarse (0.2–2 μm) and fine (–0.2 μm) clay fractions of a unique clay bed, dominated by R⩾1-type I-S were analysed for their chemical composition and dated by the K-Ar method. The fine clay fraction was dated at ~5 m.y. younger and the bulk clay to be slightly older than the known stratigraphic age, which means that the clay is mostly authigenic and formed at low-temperature, near-surface conditions. This is supported by the geological history of the region and by the variability of the clay assemblages and I-S composition within ~30 m vertical distance, neither of which indicates evidence for high temperatures. The sedimentological analysis suggests that the clay bed was deposited at marginal marine marshes where evaporated sea water turned into an alkaline solution of high K concentration. This is apparently the first study to provide convincing evidence for low-temperature, early diagenetic formation and preservation of I-S with R1-type, or similar ordering.

Authigenic illite samples have been isolated from preserved reservoir core and characterized by XRD, XRF, SEM and ATEM. Reactivity towards aqueous solutions containing acids, alkalis, complexing agents and reducing agents has been evaluated using both static (flasks) and dynamic (flow-cell) experiments at 80°C and atmospheric pressure. In flask experiments with dilute reagents, reaction appears to be simple stoichiometric dissolution. The same pattern extends to higher concentrations (molar), except for alkalis where Si is preferentially leached leaving an Al-rich residual phase. Under the more vigorous conditions of flow (continuous leaching by fresh reactant solutions), stronger acid and alkaline solutions both cause substantial dissolution although by different mechanisms. Acids displace K+ and cause illite to swell. In many of these experiments, gels were seen to precipitate downstream from the reaction site. These reactions are rapid, taking place in hours at 80°C. Similar reactions can be expected to take place in consequence of a range of drilling, stimulation and production procedures. Clay dissolution, modification and, possibly, migration would be anticipated close to the well-bore and damage from scaling (gels) somewhat further away.

13C CP MAS NMR and 29Si MAS NMR were used to characterize silylated montmorillonites and to estimate the extent of the silylation reaction. Indirectly-detected proton relaxation times of the intercalated surfactant were measured in both silylated and non-silylated clay systems to monitor the dynamics of intercalated species. A greater degree of mobility in the silylated montmorillonites was found. The lack of NMR information resulting from paramagnetic interaction brought about by structural Fe(III) ions was considered. The resulting broadening can prevent the estimation of the trans/gauche conformer ratio of the intercalated surfactant alkyl chain.

Two novel adsorbents – montmorillonite (Mnt)-hyamine and Mnt-hyamine-sodium dodecyl sulfate (SDS) – were synthesized using Mnt nanoparticles. The modified Mnt and Mnt nanoparticles were used for the removal of crystal violet from water, and they were characterized using various techniques. The effects of pH, time, temperature, adsorbent dosage and initial dye concentration on the dye-removal efficiency were investigated using response surface methodology. The optimum conditions for maximum dye removal were obtained. The optimum conditions for crystal violet adsorption on Mnt-hyamine, Mnt-hyamine-SDS and Mnt nanoparticles are temperatures 25.00°C, 29.97°C and 27.28°C; pH values 9.00, 10.41 and 9.40; adsorbent dosages 1.00, 1.15 and 1.06 g L–1; and initial dye concentrations 30.00, 98.74 and 99.44 mg L–1, respectively. The adsorbent dosage is the most critical variable for dye removal. Temkin and Langmuir are the best isotherms for studying adsorption equilibria. In the kinetic study, the fractal-like integrated kinetic Langmuir model was the most appropriate model, and the thermodynamic parameters were also determined. The synthesized adsorbents could be easily separated from solution. The Mnt-hyamine-SDS adsorbent has a high adsorption capacity (690.69 mg g–1) for the removal of crystal violet.

A clinoptilolite was exposed to treatments with acid and base solutions that caused desilication, dealumination or a combination of both. The mineralogical and physicochemical properties of clinoptilolite were studied by X-ray diffraction, X-ray fluorescence, Brunauer–Emmett–Teller specific surface area, differential thermogravimetry, Fourier-transform infrared spectroscopy and scanning electron microscopy methods. The studies provided insight into the structural and textural properties of the treated zeolite. The applied post-synthesis modification techniques proved to be effective for the generation of secondary mesopores.

It has been established that disagreements between different methods of particle size determination of clay minerals can be ascribed to the non-spherical shape of the clay particles. However, by having aspect ratios available, particle sizes can be harmonized. One frequently used approach to obtain aspect ratios is to compare particle sizes originating from at least two devices operating on the basis of different physical principles. In this contribution aspect ratios of nine kaolinite-dominated and one dickite-dominated sample were determined by conductometric titrations. The aspect ratios obtained were then successfully used to correlate particle size distributions from dynamic laser scattering and acoustic spectroscopy.

The soils over about half of South Africa are developed from sedimentary rocks of the Karoo Supergroup. Some units within the Karoo strata display variations in their mineralogical composition which correlate with fluctuations in the environment of deposition and with palaeotemperature. The former trends are reflected in the ratio of kaolinite to 2:1 layer-silicates, range from kaolinite-dominated to kaolinite-free, and are particularly evident in rocks of the Vryheid Formation. Geothermal history is preserved in various stages of smectite illitization ranging from R = 0 structures with 25% illite to 100% illite. Compositional trends may be significant on a regional, local or topographic scale down to a distance equal to the depth of a soil profile or even an horizon.

Kaolin mined from the Ipixuna deposit of Pará Pigmentos S.A. in the Capim river area of northern Brazil has been studied at various stages of beneficiation to determine the behaviour of Fe- and Ti-bearing minerals which can reduce the brightness of the product. X-ray diffraction and Mössbauer spectroscopy showed the principal pigmenting minerals to be hematite and goethite, with chemical analyses showing a distinct decrease of both the total Fe and Ti contents in the course of processing. The Ti contents were primarily reduced due to the removal of anatase during particle size fractionation and dithionite reduction. While the Fe content of the final product is structurally bound in kaolinite, Raman spectroscopy indicates the remnant Ti to be bound both structurally in kaolinite and in remnant anatase.

Sudoite, an aluminium-rich di-trioctahedral chlorite, is known primarily from highgrade diagenetic/ low-temperature metamorphic Al-rich rocks and from hydrothermal deposits in Alrich terrains. This contribution reports a rare occurrence of pore-lining sudoite in Permian red beds from the eastern part of the Southern Permian Basin. Sudoite is a ubiquitous mineral in aeolian sandstones of the Eastern Erg, a large dune field buried in the subsurface of the Fore-Sudetic Monocline, SW Poland. Sudoite crystals are arranged in a honeycomb texture and often associated with high-porosity intervals. It is concluded that sudoite crystallized at the expense of early diagenetic dioctahedral smectite at a temperature lower than 180°C under the influence of hot, Mgrich and K-poor fluids, which migrated from a basement and/or deep part of the basin upward through permeable aeolian sandstones and mixed with colder pore solutions. Tosudite was a likely intermediate phase in the smectite to sudoite conversion.

Alteration minerals dickite and kaolinite were detected in two hydrothermal Pb-Zn-Ag sulphide deposits in the northern Kosovo region. Dickite is associated with skarn mineralization in the Trepča (Stari Trg) deposit and kaolinite occurs in vein sulphide parageneses in the Crnac deposit. The mineralogical characteristics of dickite and kaolinite were determined by X-ray powder diffraction, Raman spectroscopy and scanning electron microscopy with EDS detector. Fluid-inclusion microthermometry and ion chromatography of leachates provided information on the P-T-X conditions of the genesis of dickite at Trepča. It was formed at temperatures between 290 and 330ºC and pressures between 12 and 60 MPa from a fluid with salinity in the range 6–8.5 wt.% NaCl eq. and pH <5.5. Kaolinite was deposited from a fluid with minimum temperatures between 210 and 250ºC, minimum pressure of 1.7 to 3.7 MPa, and salinity between 4.6 and 5.1 wt.% NaCl eq. Both dickite and kaolinite are related to the acidic pre-mineralization phase in the deposits.

The desorption of methanol (MeOH), propan-1-ol (n-PrOH), propan-2-ol (i-PrOH) and 2-methylpropan-2-ol (t-BuOH) from Na+-, Ca2+-, Al3+-, Cr3+- and Fe3+-exchanged montmorillonite has been studied using variable temperature infrared (IR) spectroscopy and thermogravimetric analysis (TGA). Alcohol-saturated trivalent cation (M3+) exchanged samples exhibit maxima in the derivative thermograms at 20 and 110°C (MeOH), 30 and 160°C (n-PrOH), 20 and 110°C (i-PrOH) and 20, 55 and 80°C (t-BuOH). Alcohol-saturated Na+ and Ca2+-exchanged montmorillonite samples exhibit maxima at higher temperatures in the i-PrOH (20 and 140°C) and t-BuOH (30, 90 and 110°C) desorption profiles but at the same temperatures for MeOH and n-PrOH. Mass spectroscopic analysis of the vapours desorbed from the alcohol-treated samples show that the low-temperature maxima in the alcohol desorption from the M3+-exchanged clays are due to unchanged alcohol, whilst those occurring at 80°C (t-BuOH), 110°C (i-PrOH) and 160°C (n-PrOH) are due, in the main, to alkene produced from the intramolecular dehydration of the respective alcohol. Changes in the IR spectra of the adsorbed alcohols occur at temperatures which are in accord with the mass spectral data. No mass spectral evidence was found for the formation of dialkylethers via the competing intermolecular process but dimerisation and oligomerisation of t-BuOH were observed.

Two clay deposits, the Stafford Clay marker bed from the Middle Coal Measures of North Staffordshire and the Woolhope Bentonite from the Silurian, Woolhope Limestone near Woolhope in Herefordshire are described. These clays contain mixed-layer clay minerals which have been separated by sedimentation for mineralogical and chemical analysis. Both minerals are shown to be mica-montmorillonites with MacEwan stacking parameters PA = 0·59, PAA = 0·44 and PA = 0·56, PAA = 0·70 respectively. In both cases the average layer charge (1·22 and 1·46) is intermediate between that of montmorillonites and micas but the exchangeable cation layer charge (1·07 and 1·27/montmorillonite layer) and fixed cation layer charge (1·32 and 1·63/mica layer) of the component layers are higher and lower respectively than the normal range of montmorillonites and micas. Some chemical data are given for the raw material which yielded these minerals and for associated and related rocks. In particular K, U and Th determinations permit a discussion of the natural gamma-ray flux which is sufficiently more intense than that of the associ~.ted sediments to permit its detection by scintillation counter in the field.

Chemical and mineralogical data on Holocene coastal plain soils from Thailand suggest that during formation of pyrite in tidal swamps Fe(III) is extracted from smectite and replaced by Mg. During drainage of these sediments pyrite oxidizes and the reaction is reversed. Replacing Fe(III) by Mg in clay minerals stores alkalinity that can neutralize three-quarters of the acidity released during oxidation of pyrite, and thus lowers the potential acidity of pyritic sediments. Possible causes for variation in the amounts of Mg taken up during pyrite formation are discussed.

The Corallian Beds beneath the Harwell Research Site, south Oxfordshire, are a highly variable sequence of sandstones, mudstones and limestones. The more permeable lithologies of the upper part of the sequence constitute an important local aquifer. Diagenetic and post-lithification processes have strongly influenced the porosity, permeability and mineralogy of the aquifer rocks. Calcite cementation reduced the porosity and permeability of the sandstones and limestones in the upper part of the aquifer. Cementation occurred in at least three stages ranging from early diagenesis to post-compactional diagenesis. Late-stage dissolution of calcite took place along fractures and bedding discontinuities, restoring the porosity and permeability of these sediments and developing secondary porosity and permeability where original clastic carbonate was removed. Invasion of the Corallian porewaters by waters charged with CO2 is postulated as a mechanism by which calcite was removed. At the base of the aquifer, early diagenetic dissolution of biogenic silica created a high secondary porosity. Silica was reprecipitated in the dissolution voids and matrix as opal-CT. Authigenic smectite and zeolites are also associated with opal-CT. These phases are believed to have precipitated from pore-waters rich in ions derived from the alteration of volcanogenic detritus associated with the Corallian sediments.

The Aktoprak Basin, Turkey, provides important clues regarding regional palaeoclimatic changes which have not so far been elucidated. The purpose of the present study is to fill this gap using mineralogical, geochemical and isotopic characterization of cyclic sedimentation within Neogene sedimentary units. Early Miocene alluvial-fan to cyclic shallow-lacustrine sediments of the Aktoprak Basin consist of conglomerate, sandstone, mudstone, marl, limestone and palaeosol. The increasingly fine upward grain size and bed thicknesses suggest that the alluvial fan was fed by an ephemeral braided river. The cyclic sandflat–mudflat–shallow-lake succession is predominantly composed of small-scale sandstone-mudstone beds. Sandstone intervals in the sedimentary cycles are interpreted to be a result of sedimentation from shallow, ephemeral braided-river channels, the deposits having evolved under water-saturated conditions in response to climate changes. The mudstone intervals are interpreted as having been laid down via sedimentation during distal sheet floods which developed either under sub-aerial exposure or in a water-saturated environment. Palaeocurrent measurements indicate that the general transport direction in the Early Miocene was from east to west. The lacustrine sediments of the Aktoprak Basin consist of calcite + quartz + feldspar + serpentine coexisting mainly with smectite ± palygorskite ± illite ± chlorite. Illite and chlorite are either detrital, having originated from basement units, or the illite formed authigenically from smectite. Calcite and clay appear as cement-building conglomerate, sandstone and mudstone. The clay content decreases with increasing calcite and the presence of an inverse relationship between CaO and other oxides may correspond to an inverse relationship between calcite and other minerals. Furthermore, Al2O3, Fe2O3, TiO2, MgO, Ni, Co, Cu, Sr, Ba and Zr values in the smectite-bearing mudstone and sandstone are consistent with the chemical compositions of rocks in the surrounding area, mainly ophiolitic and volcanogenic associations. Micromorphologically, the development of smectite as a cement on leached feldspar, the occurrence of palygorskite fibres as bridges between crystals and rock fragments, as well as the presence of ‘edging’ smectite flakes suggest an authigenic origin. Field observations, mineralogy, geochemistry and the results of δ18O and δ13C isotopic determinations reveal that periodic palaeoclimatic changes were controlled by alternating wet and dry periods that resulted in a relative upward decrease in precipitation of authigenic smectite ± palygorskite within the sections, under the influence of geochemical and pH fluctuations in meteoric water within the shallow-lake environment.

Clay minerals are essential components of soil systems and understanding their role in soil structure and function is critical for soil environmental quality management and sustainable agricultural development. An in-depth study of clay minerals and the development of related materials is essential for a complete understanding and effective management of soil systems. This review is a detailed compilation of relevant studies over the past decade in this area, focusing on an overview of clay minerals and their modified materials and their regulation of soil structure and function. We focus on the direct influence of clay minerals on the physical, chemical and biological properties of soils, such as soil structure, soil fertility, plant growth, soil microbial activity and soil carbon sequestration. Finally, we concluded by summarizing the existing issues with clay mineral materials in soil improvement and by outlining potential future development trends and strategies.

Five clay deposits in Foumban, west Cameroon, were studied for their morphological, mineralogical and geochemical properties to determine their suitability for ceramics. The clays were examined with X-ray diffraction, X-ray fluorescence, thermal gravimetric analysis and Fourier-transform infrared spectroscopy. Field studies showed that a homogeneous clayey layer occurs at the upper part of the laterite cover of the interfluves, while the valleys are occupied by a clayey heterogeneous hydromorphic material. The clays are composed of kaolinite, illite, smectite and chlorite, associated with quartz, K-feldspars, plagioclase, goethite, traces of rutile and hematite. Geochemical analyses of these samples show a relatively large amount of SiO2 (45–71%), Al2O3 (14–31%) and relatively little Fe2O3 (up to 11%), suggesting weathering of mainly granitic and rhyolitic parent rocks. The majority of these clays may be used in the production of structural ceramics such as bricks (refractory or not) and tiles. The relatively high proportion of the alkalis (K2O + Na2O; 6–8%) in some samples from Marom and Njindare areas might be responsible for the low firing temperatures. The abundance of smectite limits the application of some Koutaba and Marom clays for structural ceramics, while the high Fe2O3 contents (>8%) in some Bangourain clays indicate that some pre-treatment might be necessary prior to use.