Analytical transmission electron microscopy was applied to some authigenic chlorites occurring as grain coatings in sandstones. Compositional variation proved to be relatively slight: all were magnesian chamosites. The coating chlorites were often intimately mixed with extremely fine-grained (0·01–0·2 µm) hematite but analytical ‘contamination’ was avoided because of the very high resolution of both observation (spot location) and analysis. One example of a water-sensitive (‘swelling chlorite’) coating was also studied. This proved to have a very much more variable composition even within a single section. The coating appeared to include both chloritic and vermiculitic components. The effect of this on structural formulae is discussed and a model proposed in which the ‘talc’ layer may be common to both components.

The nature and origin of the clay mineralogy of the Jurassic strata of the British Isles are described and discussed within their lithological and biostratigraphical framework using published and unpublished sources as well as 1800 new clay mineral analyses. Regional clay mineral variation is described systematically for the following formations or groups:

• England and Wales

• (i) Hettangian-Toarcian strata (Lias Group): Redcar Mudstone Fm.; Staithes Sandstone Fm.; Cleveland Ironstone Fm.; Whitby Mudstone Fm.; Scunthorpe Mudstone Fm.; Blue Lias Fm.; Charmouth Mudstone Fm.; Marlstone Rock Fm.; Dyrham Fm.; Beacon Limestone Fm.; Bridport Sand Fm.

• (ii) Aalenian-Bajocian (Inferior Oolite Group): Dogger Fm.; Saltwick Fm.; Eller Beck Fm.; Cloughton Fm.; Scarborough Fm.; Scalby Fm. (in part); Northampton Sand Fm.; Grantham Fm.; Lincolnshire Limestone Fm.; Rutland Fm. (in part); Inferior Oolite of southern England.

• (iii) Bathonian (Great Oolite Group): Scalby Fm. (in part); Rutland Fm. (in part); Blisworth Limestone Fm.; Great Oolite Group of southern England; Forest Marble Fm.; Cornbrash Fm. (in part).

• (iv) Callovian-Oxfordian: Cornbrash Fm. (in part); Kellaways Fm.; Oxford Clay Fm.; Corallian Beds and West Walton Beds; Ampthill Clay Fm.

• (v) Kimmeridgian-Tithonian: Kimmeridge Clay Fm.; Portland Sandstone Fm.; Portland Limestone Fm.; Lulworth Fm.; Spilsby Sandstone Fm. (in part). Scotland

• (vi) Hettangian-Toarcian: Broadfoot Beds, Dunrobin Bay Fm. Aalenian-Portlandian: Great Estuarine Group (Dunkulm, Kilmaluag and Studiburgh Fm.s); Staffin Shale Fm.; Brora Coal Fm.; Brora Argillaceous Fm.; Balintore Fm.; Helmsdale Boulder Beds (Kimmeridge Clay Fm.).

Dominating the Jurassic successions are the great marine mudstone formations — the Lias Group, Oxford Clay, Ampthill Clay and Kimmeridge Clay. These are typically characterized by a detrital clay mineral assemblage of mica, kaolin and poorly defined mixed-layer smectite-mica-vermiculite minerals with traces of chlorite. Detailed evidence suggests that this assemblage is derived ultimately from weathered Palaeozoic sediments and metasediments either directly or by being recycled from earlier Mesozoic sediments. A potassium-bearing clay is a persistent component and formed at approximately the same time as the deposition of the host sediment, either in coeval soils or during very early diagenesis.

At three periods during the deposition of the Jurassic (Bajocian-Bathonian, Oxfordian and late Kimmeridgian-Tithonian), the detrital clay assemblage was completely or partially replaced by authigenic clay mineral assemblages rich in kaolin, berthierine, glauconite or smectite minerals. Associated with these changes are major changes in the lithofacies, with the incoming of non-marine and proximal marine strata. The authigenic clay assemblages rich in kaolin and berthierine are generally restricted to the non-marine and very proximal marine beds, those rich in glauconite or smectite are typical of the marine lithofacies. Clay mineral assemblages containing vermiculite and mixed-layer vermiculite-chlorite sometimes occur in the non-marine and proximal marine facies. The causes of these major changes in lithofacies and clay mineralogy are discussed, and present evidence favours an important volcanogenic influence and not climatic control. It is suggested that the Bajocian-Bathonian, Oxfordian and Late Kimmeridgian-Tithonian were periods of enhanced volcanic activity, with centres probably located in the North Sea and linked to regional tectonic changes which caused major modifications of the palaeogeography of the British Isles. The most important of these changes was the development of the central North Sea Rift Dome during the Bajocian and Bathonian. Volcanic ash was widespread in both the non-marine and marine environments and its argillization under different conditions provided the wide range of authigenic clay mineral assemblages.

Metre-scale clay mineral cyclicity is widespread in most of the Jurassic mudstone formations that have been examined in sufficient detail. The cyclicity is defined by systematic variations in the mica/ collapsible minerals (mixed-layer smectite-mica-vermiculite) ratio. This variation is unrelated to changes in lithology and its possible origins are discussed in detail using data from the Kimmeridge Clay provided by Reading University's contribution to the Rapid Global Geological Events (RGGE) Project.

Mineralogical analysis of Devonian Red Marl using XRD, TEM, SEM and EDAX showed that it consisted of illite, quartz, and feldspar with minor amounts of chlorite and hematite. Physico-chemical changes in the soil minerals on reaction with lime (calcium hydroxide) from one day up to two years were investigated by these techniques to gain information on the soil-lime reaction mechanism. Significant reaction of the soil minerals and lime was found to occur only at elevated temperatures (50–75°C) in a moist environment. At these temperatures, formation, growth and development of fibrous and foil-like cementitious material was observed. XRD analysis provided no strong evidence for the formation of new phases. TEM analysis and EDAX, however, showed that the newly-formed fibrous and foil-like material consisted of an amorphous calcium silicate aluminate hydrate gel, similar to the gels formed during hydrothermal treatment of lime-silica, but with lower calcium to silicon ratios than previously reported for such gels. The morphological development of the gel suggested that it formed as a result of the progressive breakdown of the clay component in the soil by reaction with the calcium ions from the lime.

The suite of London Clay mudrock samples may be sub-divided into three lithofacies: laminated silty claystone, partially bioturbated silty claystone, and partially bioturbated claystone. Mineralogically the mudrocks show little bulk variation, but considerable differences in the suites of trace cements which characterize each sample. The concretions also show a range of cement types, even within a single concretion. Preservation of uncompacted burrows and minus cement porosities (MCP) indicate that the concretions formed during early diagenesis. These data have been used to constrain the timing of authigenic mineral formation in both the mudrocks and concretions. Petrographic study of the concretions has revealed that there are significant errors involved in the use of MCP for estimation of depth of formation, which make it of qualitative rather than quantitative use. Stable isotope and chemical data suggest concretion formation occurred towards the base of the sulphate reduction zone and in the methane oxidation zone.

Production of kaolin for the paper-coating industry in the Brazilian Amazon region generates large amounts of waste, most of which is kaolinite. It is known that such materials can be used to synthesize zeolites. The use of kaolin waste for zeolite synthesis could, in principle, help social and economic development while providing valuable materials for industry. Additionally, there is a significant environmental appeal if such wastes could be used instead of new raw materials.

This study focused on the production of zeolite A. Samples of the raw material were first calcined (700ºC/2 h) to obtain metakaolinite for further reaction with NaOH solution. Different parameters were evaluated to optimize the synthesis conditions of zeolite A. The results showed that zeolite A with a large degree of structural order was generally obtained as the only zeolitic product. The following synthesis conditions were used: temperature 110ºC, time 24 h and a Na/Al ratio of 1.36. Hydroxysodalite was also obtained under specific conditions.

Clay mineralogy and its palaeoclimatic interpretation of the early-Eocene (∼53.3–49.70 Ma) sediments at Lulehe, Qaidam basin, northwest China, were investigated using optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD). The interval of ∼53.3–49.70 Ma, including the early-Eocene climate optimum (EECO) with isotopic events, was the transition period of “greenhouse” to “icehouse”. Climate changes during the episode were documented in the sediments and were expressed by the proportion of clay species and clay indices, as well as by the proportion of non-clay minerals, gypsum, halite and calcite. Our results suggest that a warm and humid climate prevailed over the period ∼53.3–52.90 Ma, followed by a warm and seasonally dry and humid climate in the period ∼52.90–51.0 Ma and a subsequently warm and humid climate in the period ∼51.0–49.70 Ma. Three warmer and more humid intervals were observed at 52.7, 51.0 and 50.5 Ma based on clay indices. The climate evolution in the Qaidam Basin during the period derived from the clay mineralogical study is in good agreement with the early Eocene global climate change, and the warm and seasonally dry and humid episode in the early Eocene in Qaidam basin is a regional response to the global early-Eocene climate optimum.

In the area of S° ile, NW Turkey, Upper Cretaceous calc-alkaline volcanic rocks with compositions ranging from andesite to rhyolite have been recognized. The most widespread rocks of the suite are andesites, which can be grouped into altered and fresh. The oldest altered andesites are the parent rocks for the kaolin deposits of the study area. The Upper Cretaceous volcanic suite consists of spilite, basalt, andesite, trachyandesite, trachyandesitic and hyaloandesitic dacite, rhyolite lavas, tuffs and agglomerates. The highly altered andesites are composed of plagioclase, pyroxene, hornblende, biotite, augite and very fine opaque minerals. During the Turonian, an E –W trending extensional magmatic arc was developed in the Istanbul Tectonic Zone of the oceanic Western Black Sea basin and intermediate volcanic rocks were emplaced, mostly calc-alkaline andesites, suggesting multi-stage magmatism. The significant features of the andesites are: (1) enrichment of LILE (Rb, Ba, K) over HFSE (Zr, Nb, Hf, Ti, Th, U, Y) and LREE (La –Sm), resulting in high Ba/Nb, Th/Nb, Ba/La, K/Ti and Th/La ratios; (2) depletion of LREE over HFSE, MREE and HREE, generating high La/Nb, Ce/Ti, La/Sm and La/Y values; and (3) depletion of Nb, Sr and Ti; all of which are typical of island arc magmatism, with possible back arc signature. The Th-Hf-Ta diagram for tectonomagmatic classification shows that the S° ile calc-alkaline rocks are similar to volcanic rocks from the Mariana Arc, the Aeolian Arc of Salina, Italy, the Skaros island in the Aegean Sea and Sardinia's ignimbrites. Moreover, relatively low La/Th and Ce/Pb ratios suggest that the source region of volcanism was enriched in LILE with respect to REE, indicating crustal contamination during melting.

Highly weathered andesitic rocks, rich in smectite, were transported gradually and deposited in a lacustrine basin, a coal-forming dysaerobic environment, in which they were subject to post-depositional alteration, or in situkaolinization, to form a kaolin deposit in the presence of humic and fulvic acids. The mobility of major and trace elements and REEs during the progressive kaolinization of andesitic materials has been investigated to reveal the geochemical characteristics of Upper Cretaceous volcanic parent rocks and to explain mineralogical processes in a kaolin deposit as a daughter rock ‘end-product’ . Alteration is characterized by the loss of Si, Fe, Ca, Na and K, and by the gain of Al, Ti, Zr and LOI. Moreover, Ho, Er and Yb are immobile, and Hf, Zr and Nb are mobile. Th and U are slightly enriched in clay horizons with respect to the andesitic rocks. In addition, Cr, Ga, Nb and Ta enrichments indicate variable sources of terrigenous sediments and differential mobilities of elements in lake waters rich in organic acids. The anatase concentration increases in the <2 mm size fractions as subspherical particles and these precipitate at acidic conditions (pH ≈ 5) during early diagenesis.

Fe-rich smectites from lateritic weathering profiles have previously been studied by XRD, ICP-AES, SEM-EDX and TEM-EDX analyses (Gaudin et al., 2004). These smectites exhibit intermediate chemistries between five end-members: Al-Fe beidellites, Al-Fe montmorillonites and Mg+Ni-saponite. The spectroscopic study by FTIR and XAS of these smectites reveals that: (1) tetrahedral Fe3+ is near or below the detection limit (0.05 cation for 4Si); (2) the large chemical variability is due to substitution of the three major cations (Fe, Al, Mg) within adjacent octahedra; (3) Ni is not concentrated in another clay phase such as Ni-kerolite and is located in the octahedral sheets of smectite; (4) octahedral cations are not randomly distributed but ordered in separated Fe, Al, Mg, Ni clusters; (5) the Mg-Ni saponite end-member actually appears as small trioctahedral clusters of Mg and Ni distributed within the dioctahedral smectite.

Four different types of natural clay were tested as potential adsorbents for toxic Pb2+ ions. Based on the preliminary screening studies, the adsorbents were effective at retaining Pb2+ ions from solution. A strong correlation was observed between the cation exchange capacity of clay samples and their function as adsorbents of Pb2+ ions. An adsorption isotherm of Pb ions on Petra clay was measured at 30ºC and at a concentration range of 0 –200 mg dm–3. Over the entire concentration range, the Langmuir isotherm gave a good representation of adsorption data, which confirms the formation of one molecular layer of adsorbate on the clay surface. Two variables were investigated to elucidate the rate-limiting steps of adsorption: the effect of initial concentration of Pb2+ and the effect of solution temperature. It is concluded that external diffusion was the only mechanism in operation in the adsorption process. It has been noted that adsorption of Pb2+ by natural clay is a fast process, where 80% of equilibrium capacity was established within the first minutes of interaction.

High-quality kaolins are produced from two sites in the Capim River area in Pará State, northern Brazil. One mine is operated by Rio Capim Caulim (RCC) owned by Imerys and the other by Pará Pigmentos S.A. (PPSA) owned by Caemi (CVRD Group). The kaolin deposits are located on low-relief plateaux with a lateritic cap. The kaolin strata are in the Ipixuna Formation of Upper Cretaceous Age. There are two distinct kaolin layers, a 4–5 m thick soft kaolin which is overlain in the southern portion of the basin by a 4–5 m thick hard kaolin. The soft and hard designations refer to particle size, with the soft kaolin being relatively coarse and the hard kaolin very fine. The kaolin is mined, partially beneficiated, and pumped through pipelines to the port at Barcarena on the Guama River, a large tributary of the Amazon River. The PPSA kaolin is fully processed at the plant near the mine site and pumped to Barcarena where it is spray dried. The RCC kaolin is only partially processed at the mine site. This partially processed kaolin is pumped to Barcarena where it is beneficiated. The finished kaolin is high quality and is shipped to North and South American, European, and Asian paper-coating markets. More than 1.6M tons were shipped from Barcarena in 2005.

The efficiency of two low-cost, abundant and natural clay minerals, palygorskite and vermiculite, in terms of reducing the concentation of Cu2+ and Ni2+ ions was evaluated here. Natural clay minerals were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), BET specific surface area and pore-diameter analysis. Batch-type experiments were performed and various parameters, i.e. pH, clay amount, contact time and initial metal concentration, that affect adsorption processes were investigated. The adsorption of Cu2+ and Ni2+ ions is pH-dependent, while minor clay quantities were sufficient to achieve high removal efficiencies. Adsorption equilibrium occurred in 60 min and the adsorption kinetics were better described by pseudo-second-order kinetics. Experimental results were analysed by the Langmuir, Freundlich, Dubinin–Radushkevich (D–R), Temkin and Halsey isotherm equations. The release of exchangeable cations (i.e. Ca2+, Mg2+, Na+ and K+) was examined to verify an ion-exchange mechanism.

The adsorption of aminotriazole, at its solution pH, with montmorillonite saturated with different cations has been studied. A pesticide-montmorillonite complex is formed through interlamellar cations which are not displaced. Aminotriazole is situated mostly as a polarized molecule around Mg2+ and Zn2+ cations, removing a great amount of water. In Na+- and Li+-montmorillonite, the pesticide remains as a non-polarized molecule, hydration water being retained in the interlamellar space; the pesticide is coordinated to interlamellar cations through water bridges. For all samples a proportion of cationic aminotriazole is also adsorbed, the amount being greater with increasing polarizing power of the interlamellar cation; consequently, in Fe3+-montmorillonite all the aminotriazole adsorbed is in the cationic form.

The clay mineralogy of K-fixing soils from southern Germany was investigated using the alkylammonium method. Conventional X-ray diffraction chart recordings of glycerol-saturated <0·1 µm samples showed peaks at 18 Å that were initially interpreted as smectites. However, step-scanning combined with the Lorentz- and polarization-correction and curve-fitting, revealed the presence of low- and high-charge smectites and of low- and high-charge vermiculites. The severe overlap of the 001 basal reflections of the high-charge vermiculites with the broad and intensive peaks of smectites sensu stricto prevented visual evaluation at the alkylchains nc = 5–9, but this problem was overcome by curve-fitting. The 002 peaks of high-charge vermiculites (nc = 8 and nc = 10) in the fraction 0·1–0·2 µm could furthermore be clearly resolved from the 001 peaks of illite by curve-fitting. In one example, 003 (at nc = 17) could be resolved from 001 of illite.

The aim of this paper is to show how van der Waals forces may account for profound changes in the IR spectra of alkylammonium saturated montmorillonite and the effect of adsorbed water molecules. IR spectra recorded on alkylammonium montmorillonite films submitted to vacuum and after exposure to water vapour show, in addition to the shifts in the stretching and deformation bands expected when hydrogen bonding is present, marked changes in the intensity of the CH2 and CH3 deformation bands. All these observations are explained by the following model: (1) in the absence of water, the aliphatic chains are tightly held between the oxygen atoms of the silicate layers with their axis parallel to the 001 planes; and (2) hydration causes a rotation of the organic chain of the dialkyl derivatives while it does not affect the orientation of the monoalkylammonium cations. Moreover in the former situation, the symmetric deformation band of CH3 is removed because of the increase of the reduced mass due to the immobilization of the chain between the oxygen atoms.

The kaolinized granites of St. Austell, England, are worked to produce a range of china clay products, for some of which the kaolin has to meet stringent particle shape and size specifications. Systematic petrographic study indicates that kaolin occurs in the form of two textural types: (i) finely crystalline kaolin (typically <5 µm in average diameter), which infills dissolution porosity of granitic feldspars, and (ii) coarsely crystalline vermiform aggregates (up to 100 µm or more in length), which are closely associated with expanded micas. The vermiform aggregates are characterized by an intergrowth of mica and kaolin crystals, which can be observed at scales of resolution offered by TEM. Textural and chemical evidence suggest that the expanded mica texture is probably the result of preferential precipitation of kaolin along mica cleavage planes and is not simply a process of chemical replacement.

Petrographic examination of kaolin slurries sampled at different points in a typical refinery circuit indicates that platy products with high aspect ratio are derived exclusively from raw materials rich in vermiform aggregates. The fine scale intergrowth of kaolin and mica within the aggregates results in circumstances where mica persists through to fine grained products. Furthermore, the absence of Fe or other chemical components in the kaolin structure suggests that any iron reported for the final products may be a consequence of the presence of Fe-bearing mica within a very fine grained intergrowth.

The kinetics of the dehydration of ethanol on acidic Al3+-exchanged sepiolite has been studied. The product distribution indicates that the formation of diethylether and ethylene takes place by a series of consecutive and parallel reactions. A mechanism for the formation of both products has been derived by studying the influence of different operational variables on the reaction rates.

Two sets of natural Al-substituted goethites from contrasting surface environments (24 tropical and subtropical soils vs. ten lake iron ores from Finland) were characterized by Mössbauer spectra obtained at room temperature and 4.2 K. A negative correlation between Bhf and Al substitution (R2 = 0.751) was found by combining the data of all the samples, which was slightly improved (R2 = 0.779) by taking the mean coherence length perpendicular to 111 (MCL111) into account. The effect of Al on lowering Bhf was, however, stronger for the tropical soil goethites than for those of the lake ores. This is parallelled by a corresponding difference in the unit-cell decrease per unit Al substitution. These differences are believed to result from the crystallization conditions in the two different environments.

The nature and composition of the Fe minerals in the rusty ferruginous material frequently located in the zone of contact between the thallus of Stereocaulon vesuvianum and the leucite bearing rock of Mt. Vesuvius have been studied by microscopic and submicroscopic investigations (SEM, TEM with EDXRA) complemented by X-ray diffraction and chemical analysis. Ferrihydrite is likely to be the main component of the short-range order iron oxyhydroxide pool, although the possibility that significant feroxyhite may be present cannot be completely excluded. Hematite and goethite are the crystalline iron oxides. The organic acids produced by lichens play a key role in the enrichment of poorly-ordered phases at the rock-lichen interface. It is suggested that the peculiar morphology of the Stereocaulon vesuvianum thallus and the irregularity of the volcanic rock surface lead to different microsites in the rock-lichen interfaces which have their own conditions of pH, humidity and redox potential, favourable for the neoformation of crystalline phases.

An experimental investigation was conducted on the alkali activation of a kaolinitic clay using an alkaline mixture composed of hydrated lime (Ca(OH)2) and sodium carbonate (Na2CO3) solution. The Ca(OH)2/Na2CO3 alkaline mixture was developed to overcome the high cost and chemical aggression associated with classical alkaline solutions. The mineralogical composition and microstructure of the alkaline mixture and alkali-activation products were studied using X-ray diffraction, attenuated total reflectance-Fourier transform infrared spectroscopy, thermogravimetric analysis and energy-dispersive X-ray-scanning electron microscopy techniques. Pirssonite (Na2Ca(CO3)2·2H2O), calcite (CaCO3), and sodium hydroxide (NaOH) formed as a result of mixing of Ca(OH)2 with Na2CO3. The alkali activation of natural clay with the Ca(OH)2/Na2CO3 alkaline mixture produced a binding agent identified as hydroxysodalite phase (Na8Al6Si6O24(OH)2·4H2O) when pure kaolinite was used, and cancrinite carbonate (Na6Ca1.5[Al6Si6O24](CO3)1.5·1.8H2O) when kaolinitic clay with high a calcite content was used. The mechanical strength of the binder developed was evaluated on cylindrical specimens containing granite waste as a filler material under dry and soaked conditions. The classical NaOH activator was used for comparison. For specimens produced using a Ca(OH)2/Na2CO3 mixture as the alkaline activator, the recorded strength valuewas 21 MPa which was 35% less than that achieved by the classical NaOH solution. Durability tests on samples soaked in water for 24 h showed a reduction in strength from 34 to 22 MPa for specimens prepared with NaOH solution, and from 21 to 11 MPa for the specimens prepared with a Ca(OH)2/Na2CO3 alkaline mixture.