Selected-area electron diffraction has been used to examine ferrihydrite coatings on kaolinite crystals and is shown to provide a sensitive means of detection. It also gives better diffraction patterns of ferrihydrite than does XRD and the patterns sometimes give additional indications of the crystal size. It is suggested that the technique may be useful in examining other coatings on soils and clays.

A number of bentonitic clay deposits from the Ordu area (NE Turkey) have been investigated by optical and electron microscopy, X-ray diffraction and chemical analysis. The clays are the alteration products of Late Cretaceous trachytic and trachyandesitic pyroclastic rocks. They contain volcanogenic sanidine, plagioclase, biotite and pumice, along with the diagenetic minerals opal-CT, cristobalite and rare calcite and zeolite (clinoptilolite). Ca-smectite (montmorillonite) is the dominant clay mineral. The rare earth element patterns of all the bentonitic clays are generally similar, although there are variations in the Eu anomaly indicating formation from different types of pyroclastic rocks. Oxygen and hydrogen stable isotope values suggest that the smectite was formed at 20–40°C in pore water of mixed meteoric and marine origin during argillization. These features, together with mass-balance calculations, indicate the enhanced MgO and Sr content of the smectite resulted from formation at shallow burial depths within a dominantly marine environment.

Illite age analysis (Pevear, 1992) and similar mixing methods demonstrate nearlinear behaviour when corrected for smectite content in illite-smectite and substitutions for K+ in illite layers. Srodon (1999) found that highly curved mixing lines result from theoretical calculations and challenged the validity of IAA. However, our theoretical calculations indicate near-linear mixing lines result when corrected for the amount of smectite and known K+ substitutions (Na+ or NH4+). We conclude that perfect linearity is unattainable because IAA attempts to unmix a system linearly, but the system is based on an exponential function (K-Ar equation). In practice, we believe IAA can successfully determine the age range of illite diagenesis, even though perfect linearity is not attainable because: (1) significant deviations from linearity occur only if >500 Ma separate the diagenetic and detrital ages; (2) IAA analytical uncertainties result in diagenetic and detrital ages that span a range of ages.

Although differential thermal analysis can now be used to assess the complete constitution of clays and many ceramic materials the silica minerals present many unusual difficulties. The importance of silica and siliceous materials for refractory purposes, the changes which take place in such materials on firing, and the influence of the constitution on the properties of the final product, necessitate a rapid and reliable method for the identification and estimation of the silica phases. Chemical methods cannot differentiate between the various types. X-ray analysis although useful for identification purposes, cannot as yet be used for estimation of the three phases, when all are present together.

The use of preferentially oriented aggregate specimens of clay for X-ray diffraction has been widely adopted since its origination by Bradley, Grim and Clark (1937). It is an extremely useful technique giving greatly enhanced intensity of diffraction from the basal planes of platey minerals relative to that from the general planes; the amount of one particular clay mineral which can be identified in a mixture is very much less than by the normal powder method.

Van Houten (1973), Walker (1976) and Turner (1980) have documented the authigenic origin of red coatings in continental red beds. Pigmentary hematite, ferrihydrite, goethite and clay-associated Fe-oxide crystallites have been suggested as the principal colouring agents of continental red beds (Walker, 1968, 1976; Walker & Honea, 1969; Larson & Walker, 1975; Turner, 1980; Fine, 1986, Besly et al., 1993). The red pigment in most Mesozoic red beds consists of hematite, whereas ferrihydrite and goethite are more common in younger sediments (van Houten, 1973). This has led several authors to the assumption that poorly crystalline Fe-oxides/hydroxides age into hematite (Walker, 1968, 1976; Walker & Honea, 1969; Larson & Walker, 1975; Turner, 1980).

A swelling chlorite from unweathered basalt has been characterized by XRD, IR, DTA and chemical analysis. Its 001 spacing of 14.9 Å increases to 18.0 Å on treatment with glycerol and decreases to 13.9 Å (with a broad diffraction effect at 14-10Å) after heating to 550°C. The mineral has an 060 spacing of 1.537Å consistent with a trioctahedral composition, but its OH stretching band at 3638 cm−1 does not show the expected pleochroism, suggesting an anomalous hydroxide sheet which chemical analysis shows is incomplete. Although the mineral has a CEC of ∼50 mEq/100 g, smectite is not present, but all the techniques show that the mineral has some saponitic character, indicating that it probably has a structure intermediate between swelling chlorite and saponite.

A bentonite from Milos, Greece, was activated with oxalic acid and the effect of acid activation conditions on bleaching of sunflower oil was investigated. The activation parameters studied were temperature, retention time and oxalic acid to bentonite mass ratio. The activated materials produced had good bleaching properties and were suitable for industrial use as bleaching earths. Optimum bleaching properties could be achieved using a variety of combinations of acid to bentonite ratios and activation times. Bleaching efficiency tests indicated that 24 h activation at 100°C with 1m oxalic acid and 25% pulp density (w/v) gave results equivalent to that of a commercial bleaching earth (Tonsil Optimum 210 FF). The combination that is likely to be more preferable on an industrial scale was 100°C, 25% pulp density (w/v), 1m initial oxalic acid concentration, 60% recycling of the oxalate solution (making up an acid to bentonite ratio 0.2 w/w) and 6 h activation time. The materials produced under these conditions have acceptable bleaching properties, corresponding to bleaching capacity greater than 78% compared to commercial Tonsil, and colour index (in red and yellow units) equal or even better than Tonsil.

Secondary clay minerals observed in the two uppermost basalt lava flows at ODP Site 1001, in the Caribbean Sea, drilled from the large igneous province of Cretaceous age, result from low-temperature alteration processes. Alteration mainly proceeds by circulation and diffusion of sea water. Six different types of clay mineral assemblage were recognized. Initial alteration with oxygenated sea water involves Fe and K fixation, creating visible oxidation halos parallel to the sides of cracks and fissures. A saponite/ beidellite mixture, interstratified smectite-glauconite, interstratified glauconite-nontronite and Fe oxyhydroxides are obtained depending on the distance from fluid conduits. The presence of beidellite may be due to enhanced Al mobilization resulting from high fluid flux. These early minerals are cross-cut by thin veins of pure celadonite or glauconite with further vesicle infill. Late-stage alteration is typified by the formation of saponite and takes place under closed reducing conditions resulting from deposition of the sedimentary overburden.

L'analyse par diffraction des rayons X, résonance paramagnétique électronique et par spectrométrie infra-rouge des constituants minéraux du profil des Canonnettes (Sud-Est de la France) permet de montrer que les kaolinites sont ferrifères. De plus, au fur et à mesure du développement et de l'accumulation des oxy-hydroxydes de fer et d'alumine dans le profil, on note l'enrichissement progressif des kaolinites en fer en même temps qu'augmente leur désordre et que les taux de substitution en moles % d'AlOOH des goethites alumineuses devient plus important. Finalement, les kaolinites disparaissent remplacées par les oxy-hydroxydes de fer et d'aluminium, là ou leur accumulation est maximum.

Interlayer K from two biotites of different origin was extracted with octadecylammonium chloride (ODA) and sodium chloride/sodium tetraphenylboron (STB) before and after oxidation with saturated bromine water (Br2). Potassium release, Fe oxidation and Fe ejection from octahedra were measured. With ODA and STB the untreated biotites released between 40 and 90% of initial interlayer K, the muscovite less than 5%. After Br2 treatment, substantially less K was extracted from both biotites. Suppression of K release was caused by the formation of octahedral vacancies formerly occupied by Fe. The extent of Fe ejection was not proportional to the extent of octahedral Fe oxidation. During Br2 treatment, the biotites transformed into hydrobiotite. The hydrobiotite sample, high in Fe ejection during preceding Br2 treatment, strongly resisted subsequent K extraction with STB, whereas the sample with minor Fe ejection transformed to vermiculite. Octadecylammonium chloride extracts K more effectively than STB from biotites intermediate between trioctahedral and dioctahedral structure and is considered to be suitable for the distinction between biotite K and muscovite K.

Highly crystalline kaolinite has been studied by 27Al satellite transition magic angle-spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. This technique provides an additional narrowing of the MAS spectral lines by a factor of more than three compared with the width of the prominent central transition. Evidence for the presence of two crystallographically inequivalent hexacoordinated Al sites has been found. The results support the kaolinite crystal structure proposed by Bish & Von Dreele (1989).

L'auteur étudie l'absorption par une montmorillonite H-AI, d'acides organiques extraits d'Andosols dans une gamme de pH allant de 1,5 à 5. Quand il y a absorption entre les feuillets, on observe une résistance particulière de la montmorillonite à l'écrasement après chauffage, même pour des températures supérieures à 500°C Un complexe organo-minéral ou organique résistant à la chaleur se forme entre les feuillets de la montmorillonite, comme le révèlent les courbes d'ATD et les spectres IR. On retrouve les propriétés originelles de la montmorillonite par peroxydation.

Des argiles gonflantes 2/1 à complexes organo-minéraux et/ou organiques entre les feuillets sont observées dans les Andosols. Les propriétés de telles argiles rappellent en partie celles des chlorites gonflantes ou des pseudochlorites.

Smectite-rich clays are to be used in nuclear repositories for sealing in the radioactive waste. As the radioactive decay produces heat it may affect the chemical, physical and hydromechanical properties of the clay components in the repository. An ‘alternative buffer material’ (ABM) experiment is a Svensk Kärnbränslehantering AB (SKB)-led in situ heating test placed in boreholes in the Äspö tunnel (Sweden). The 2nd ABM package was dismantled in April 2013, after 6.5 y of equilibration with Äspö groundwater and 5 y of heating. The objective was to investigate the long-term effects of the iron heater and Äspö groundwater on four of 31 compacted blocks made of MX-80, Deponit CaN and Friedland clays.

Compared to the starting materials, major changes in the exchangeable cation populations were observed. Within horizontal profiles, water-soluble sulfate, Ca, K and Mg increased; poorly crystalline Fe oxide contents decreased; total Mg, Ca and S increased; and a decrease in the amounts of total Na and K away from the host rock towards the heater was observed. At the boundary with the heater, an increase in the total Fe content, decreases in total Si and Al contents, precipitation of gypsum and anhydrite, dissolution of cristobalite and feldspars, and indications of the formation of trioctahedral clay minerals were observed. A decrease in swelling pressure for the Friedland clay (in drill-cored samples) was recorded which was recovered after grinding and recompaction. No effects of hydraulic conductivity were found, after 6.5 y of reaction time, in the subsurface of any of materials studied.

Nanometre-sized illite-type crystals extracted from mixed-layer illite-smectite of cored bentonite beds from the East Slovak Basin were studied to investigate timing, duration and physical/chemical conditions of their nucleation and growth. The study includes application of the results to an evaluation of the regional extent of illitization. Close to salt-bearing formations, the nanometric particles underwent a more intense illitization, of identical duration, but with changing oxygen and hydrogen isotope characteristics of the parental brines.

A comparison of the stratigraphic ages of the bentonite beds with the K-Ar ages of the authigenic crystals shows that illitization started during the Middle-Miocene Serravalian (Lower Sarmatian) subsidence that lasted from 17 to 11.5 Ma. Duration of illitization was bracketed between 14.5 and 9.0 Ma, with further episodes until recently at 0 Ma, depending on the geographic location of the host beds. The calculated subsidence rate varies from less than 300 m/Ma to more than 500 m/Ma and the thermal gradient ranges from ~60°C/km to less than 50°C/km. The K-Ar ages of the nanometric illite point to either short-duration illitization when the onset was soon after sedimentation, or long-duration when the onset was significantly later after sedimentation. The illite δ18O varies little with increasing crystal size, whereas the δD changes significantly. In most samples the crystallization temperature determined by different criteria did not change significantly during crystal growth, but the oxygen and hydrogen isotopic compositions of the interacting fluids varied depending on sample location, immediate environment, timing and duration of illitization.

The stable isotope composition of illite in bentonite beds with reduced fluid-rock ratios gives insight into the fluid-temperature regime of sedimentary basins through identifying local processes rather than wide-scale ones. Illitization is episodic with variable duration along different crystallization pathways, and to various extents in low-porosity, low-permeability bentonite beds. Depending on local conditions, illitization may vary even within apparently homogeneous beds. This contrasts with the situation for porous aquifers having large-scale fluid connectivity.

A halloysite clay from Nador (NE Morocco) was studied to evaluate its suitability in the ceramics industry. A cross-section involving all the Messinian facies was performed in the Melilla Neogene basin, at the foot of the Gourougou volcano, to establish the origin of the halloysite and estimate its reserves. White layers of halloysite and red clays rich in smectite occurring in contact with basal-reef limestone were characterized by mineralogical (XRD, IR), textural (SEM) and physico-chemical analyses (grain-size, Atterberg limits, DTA/TG, XRF and specific surface area). Ceramic properties were evaluated for halloysite fired from 500 to 1100°C to evaluate technical processing for ceramic production.

The halloysite clay consists of fine particles with a high plasticity and a large specific surface area. The XRD investigation revealed the presence of 7 Å non-hydrated halloysite along with gibbsite, alunite, K-feldspar and traces of smectite and illite.

The presence of halloysite was confirmed from the characteristic IR bands at 3695 and 3618 cm−1 and the predominance of tubular crystals observed in the SEM. The chemical analysis revealed high contents linked to the presence of Al-rich phases (gibbsite and alunite). DTA/TG and XRD results of fired clay samples proved the dehydroxylation of halloysite and a rearrangement of metakaolinite to form mullite and spinel at 975°C.

The Moroccan halloysite might be suitable for refractory ceramic applications. However, addition of quartz sand might be necessary to avoid crack development during firing and to reduce the plasticity of raw halloysite and minimize shrinkage during sintering.

Complex formation enhances the sorption of various diamines from aqueous solutions by montmorillonite in the presence of copper and vice versa. A distinct difference was observed between chelating and nonchelating diamines. The effects were measured quantitatively, and the resulting structures were investigated by X-ray diffraction tedhniques. No direct correlation was observed between cell height and the configuration of the interlayer complexions; ‘keying’ of organic and organometallic cations into the oxygen surfaces is inferred.

A natrolite-cemented palagonite ash tuff unit is reported in a palaeo-basin in northeast Jordan. Phillipsite and chabazite are also identified. The zeolites were formed due to transformation of volcanic glass granules into palagonite by the reaction with percolating water in a closed hydrological system. Consequently, Si, Al, Ca, Na and K are leached out and precipitated in a series of authigenic layers developed at the extreme edge of the granules. The recorded paragenetic sequence is smectite → phillipsite → chabazite → natrolite → analcime → calcite. The natrolite studied is chemically similar to those reported in the literature with minor variations. The phillipsite and chabazite studied are chemically different from the other Jordanian phillipsite and chabazite reported. The latter are chemically equivalent to those formed under open hydrological systems, whereas the phillipsite and chabazite in this study are chemically equivalent to those formed in saline lakes and arid soil environments. This conclusion is based on the (Na+K)/(Na+K+Ca+Mg) ratio and the Si/Al ratio.

An investigation of bulk-rock and clay-fraction compositions of two sedimentary cores from southern Chile was performed to evaluate the record of temporal climatic changes during the late Quaternary (11 ky and 30 ky BP). The bulk mineralogy shows an abundance of feldspars, mica and quartz, with lesser chlorite, amphibole and pyroxene, and variable amounts of carbonates. The clay fraction consists of illite, chlorite and scarce smectite. Smectite shows platy morphology, an Al-Fe beidellite chemical composition, and is detrital. Smectite, together with biogenic carbonate, increases in levels diagnostic of warmer phases. Increases in smectite are attributed either to the beginning of chemical weathering, allowed by the glacial retreat, or to ice extension and sea-level variations. Warmer climates also favoured the increase of carbonate productivity. Levels diagnostic of colder phases show a large decrease in carbonate, small amounts of smectite and large amounts of chlorite and mica, as the abundance of glaciers reduced the productivity and prevented chemical weathering.

An XRD-TEM study was carried out on low-grade metapelites (Transantarctic Mountains) to determine the cause of apparent inconsistences in grade as determined by IC and independent geologic relations. The illite crystallinity (IC) data indicate that the three units investigated (BT, RBT, MS) were affected by very low- (IC = 0.24°Δ2θ in BT) to low-grade metamorphism (0.19°Δ2θ in MS). In all three samples, mica crystals are of a size typical of the epizone, but the mean size increases from BT to RBT and MS, due to the increasing strain features from BT to MS. These results indicate that strain-induced reduction in crystal size was retained in BT samples (with anomalously high IC values). Microtextures in RBT and MS (with smaller IC) samples suggest a recovery of sub-grain boundaries. A decrease in crystal size may occur with increasing grade where strain rates are high relative to the rate of recrystallization.