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.

Hydrolytic exchange was performed experimentally on four smectitic clays to evaluate the extent of clay alteration induced by this process and the associated ‘auto-transformation’ of H+ clays. Clay samples were Na-saturated and submitted to 10, 50 and 100 wetting-drying (WD) cycles and characterized after treatment using X-ray diffraction (XRD), infrared spectroscopy (FTIR) and cation exchange capacity analysis. Evidence for hydrolytic exchange was given by increasing amounts of exchangeable Mg2+ and precipitation of Na soluble salts for samples subjected to 100 WD cycles. Results indicated a decrease in the interlayer charge after 10 WD cycles but no further decrease was observed after 50 and 100 WD cycles. For one sample, XRD data indicated a decrease in the proportion of the smectite phase and a relative increase in the concentration of illite-smectite mixed layers also present in the sample. The results suggested that the reaction induces first a decrease in the layer charge and then a partial dissolution of some smectite layers.

This work describes the possible use of thick Early Cretaceous clay deposits, which occur in the southern sector of the Sierra de la Demanda range, as raw materials in the manufacture of ceramic articles. The global mineralogical composition is characterized by high proportions of phyllosilicates and quartz with variable quantities of feldspars, carbonates and hematite. The clay mineralogy differentiates two types of raw materials: illitic clay and kaolinitic-illitic clay. A granulometric distribution in the 2–60 µm fraction, good behaviour during the drying stage and acceptable results in firing tests confirmed that most samples can be utilized as raw material in the building ceramics industry. The range of suitable firing temperatures for these materials is 950–1000°C, a temperature which needs to be raised for samples with a high percentage of kaolinite and quartz. Moreover, other materials with abundant calcite (20–30%) are suitable for use as modifiers of some properties or colour.

The clay mineral assemblages and microtextures of a suite of mudrocks from the Lias Group of England and Wales indicate important regional differences in burial history.

Samples from the northern Cleveland Basin are characterized by illite-smectite (I-S, 90% illite) and little carbonate whilst samples from the southern Worcester and Wessex basins contain less mature discrete smectite and are often calcite- and dolomite-rich. Lias Group rocks have been buried to 4 km in the Cleveland Basin but to <2 km in the Worcester and Wessex basins. Burial in the Cleveland Basin is deeper than previously estimated and does not need a local heating event. Illite- smectite (80% illite) detected in samples from the East Midlands Shelf suggests burial to 3 km, again deeper than previous estimates for this region.

At 25°C, synthetic schwertmannite, a common iron compound in acid mine drainage, completely converted in water to a sulphate-containing goethite within ~100 days. The rate of transformation doubled as the pH increased from 4.0 to 7.2. In deviation from its normal acicular habit, the goethite appeared as spherical aggregates.

Clay minerals occur as replacements of olivine, pyroxenes, plagioclase and interstitial materials, and as vesicle fillings, in altered basalts from the Middle Atlas (Morocco). Phyllosilicates are the main components of this alteration process. They have been characterized here by optical microscopy, X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy as saponite, talc, corrensite and chlorite. The homogeneity of the chemical compositions of these phyllosilicates, in different alteration environments, probably means that they are controlled by the composition of the hydrothermal fluid. Talc-saponite-corrensite (with dominant saponite) is the clay mineral association most frequently observed (corrensite being more abundant in the vesicular levels of the basalts). Such an association, with no evidence of albite and zeolite, suggests that these basalts have suffered minimal alteration at relatively low temperatures. Another association, chlorite-corrensite, was detected in a deeper (vesicular) sample, probably resulting from a slightly higher temperature. Lastly, only discrete phyllosilicates (i.e. no random mixed-layer minerals) were observed. This suggests that near-equilibrium conditions prevailed during this alteration stage and that a dissolution-crystallization process was the main mechanism of transformation.

Variations in clay mineral assemblages, changes in Kübler index (KI), and the chemical composition of chlorites are used to identify source areas in the lacustrine materials in the Lower Cretaceous Leza Limestone Formation of the Cameros Basin, northern Spain. This formation has fairly homogeneous lithological characteristics and facies associations which do not allow for identification and characterization of local source areas. The Arnedillo lithosome of the Leza Limestone Formation contains a clay mineral association (Mg-chlorite, illite and smectite) indicative of its provenance. Chlorite composition and illite KI values indicate that these minerals were formed at temperatures higher than those reached by the Leza Formation which indicates its detrital origin. The similarity in the Mg-chlorite composition between the Arnedillo lithosome and the Keuper sediments of the area indicates that these materials acted as a local source area. This implies that Triassic sediments were exposed, at least locally, at the time of deposition of the Leza Formation. The presence of smectite in the Leza Formation is related to a retrograde diagenesis event that altered the Mg-chlorites in some samples.

Pelitic and basic rocks occurring within prograde sequences in Portugal, Spain and Hungary have been studied by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The minerals formed in typical prograde reactions define the general sequences, but smectite, chlorite-smectite (corrensite) and/or berthierine were found to have replaced chlorite, whereas kaolinite and mixed-layer illite-smectite replaced illite-muscovite. Alteration occurred under conditions normally associated with diagenesis, subsequent to regional metamorphism, and we therefore refer to such processes with the term “retrograde diagenesis”. In the cases studied and in other cited examples, reactions occurred on a regional basis via pervasive fluids under open-system conditions inferred to be related to tectonic stress. The observed alterations could generally not be inferred from XRD data, although the presence of pure smectite in sediments other than bentonite is suggestive of retrograde relations, especially where other minerals are consistent with a higher grade of diagenesis. Retrograde diagenesis is readily observed through imaging of textures by TEM, however. Textural features show that retrograde reactions are more common than generally assumed, and that care should be used in interpreting geological events where appropriate textural relations are not seen.

This study focused on whether the presence of clay minerals (montmorillonite and kaolinite) in marine or coastal environments contaminated with high concentrations of heavy-oil spills were able to support the growth of hydrocarbon degraders to enable bioremediation. The bacterial growth experiment utilizing ~150 g/l of heavy oil (from the Nakhodka oil spill) was conducted with 1500 mg/l of montmorillonite or kaolinite. Bacterial strain Pseudomonas aeruginosa (isolated from Atake seashore, Ishikawa Prefecture, Japan), capable of degrading heavy oil, was employed in combination with other hydrocarbon degraders inhabiting the heavy oil and seawater (collected from the Sea of Japan). The interactions among microbial cells, clay minerals and heavy oil were studied. Both clays were capable of promoting microbial growth and allowed microorganisms to proliferate (to a greater degree than in a control sample which contained no clay) in an extremely high concentration of heavy oil. Observation by transmission electron microscopy of the clay-oil-cell complexes showed that microbial cells tended to be bound primarily on the edges of the clays. X-ray diffraction analysis showed that the clay-oil and clay-oil-cell complexes involved the adsorption of microbial cells and/or heavy oil on the external surfaces of the clays. How do the interactions among clay minerals, microbial cells and heavy oil contribute to environmental factors influencing the bioremediation process? To our knowledge, there are no previous reports on the use of clay minerals in the bioremediation of the Nakhodka oil spill in combination with biofilm formation.

The origin of the regional and stratigraphical variation in the Triassic authigenic clay assemblages of England is discussed in relation to new estimates of the palaeotemperatures experienced by their host sediments and a preliminary study by transmission electron microscopy of their microtextural features. Spore colour index measurements, based on the spore type Deltoidospora s.l. occurring in the sediments (Penarth Group) at the very top of the Triassic sequence, give estimated palaeotemperatures ranging from 60–74°C (south Devon) to 89–97°C (northeast Yorkshire). Calculated palaeotemperatures, based on a gradient of 25°C/km, for the main zone of authigenic clay minerals range from 63–77°C to 89–97°C for the top to 71–85°C to 94–104°C for the base. Irregular mixed-layer smectite-chlorite, corrensite and Mg-rich chlorite are associated with calculated palaeotemperatures of 66–86°C, 66–104°C and 75–104°C respectively. The suggestion that elsewhere in the UK corrensite and Mg-rich chlorite were formed at temperatures in excess of 100°C finds no support. Geothermal gradients would have to have been of the order of at least 100–300°C/km to obtain these temperatures within the Triassic sediments; such values are associated typically with high-level magmatic intrusions or geothermal systems of which there is no geological evidence. The balance of evidence suggests that the Triassic authigenic clay assemblages formed by neoformation during the early stages of sediment diagenesis under the influence of variation in the alkalinity of the depositional environments.

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.