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.

A 65 m thick altered volcanic profile was studied in the Cava di Caolino (Lipari Island) in order to (1) identify the alteration event(s), (2) model these events, and (3) propose estimates of the degree of chemical alteration (CIA, chemical index of alteration). Two mineral parageneses were identified: one comprising silico-aluminous phases, with well crystallized kaolinite (type 1), and the other comprising sulphates, with kaolinite as fracture infilling (type 2). The geochemistry of fluids analysed from a local hot spring (40°C, pH ≈ 8) allowed modelling of the observed silico-aluminous paragenesis. A later fumarolic event is suggested to be responsible for the sulphate paragenesis. The main stage of hydrothermal alteration lasted for ~50 ky, was marked by an increase in the CIA from the protolith (~52) to the alterites (~98), and resulted in the alteration of a 65 m thick series. Such data could be used to predict the alteration of volcanic rocks around underground nuclear waste repositories.

The Lòn Ostatoin stream section, Trotternish Peninsula, Isle of Skye, exposes a sequence of Middle Jurassic mudstones and limestones which have been locally metasomatized by a transgressive sill of Tertiary age. Limestones in the sequence, including some previously reported as bentonite, have been altered to an unusual assemblage of grossular garnet and saponite clay. The mudstones also contain large proportions of saponite together with pyroxene and zeolites. Saponite also occurs within the basalt intrusion. Grossular and pyroxene represent artifacts of relatively high-temperature assemblages that formed during an early phase of alteration. As the intrusion and adjacent altered country rocks cooled, lower-temperature fluids flowed through a late set of contraction (micro)fractures. Back-reacted saponite, analcime and clinoptilolite were formed, possibly as alteration products of the unstable higher-temperature minerals. The lower-temperature mineral assemblage eventually sealed the late fracture system.

This paper highlights an important concept for the study of analogue sites used to investigate thermal effects on engineered liners or barrier host rocks for the landfill and radioactive-waste industries. This is that the original thermally altered mineral assemblage may be overprinted by later, lower-temperature back-reactions. A detailed understanding of both processes is necessary in order to construct a sensible model for the thermal and mineralogical evolution of the site.

Halloysite clay minerals are ubiquitous in soils and weathered rocks where they occur in a variety of particle shapes and hydration states. Diversity also characterizes their chemical composition, cation exchange capacity and potassium selectivity. This review summarizes the extensive but scattered literature on halloysite, from its natural occurrence, through its crystal structure, chemical and morphological diversity, to its reactivity toward organic compounds, ions and salts, involving the various methods of differentiating halloysite from kaolinite. No unique test seems to be ideal to distinguish these 1:1 clay minerals, especially in soils. The occurrence of 2:1 phyllosilicate contaminants appears, so far, to provide the best explanation for the high charge and potassium selectivity of halloysite. Yet, hydration properties of the mineral probably play a major role in ion sorption. Clear trends seem to relate particle morphology and structural Fe. However, future work is required to understand the possible mechanisms linking chemical, morphological, hydration and charge properties of halloysite.

Mine-drainage waters and associated precipitates from several active and abandoned lignite mines and mine dumps in the Sokolov Basin, northwestern Czech Republic, were sampled and analysed. The data showed considerable variations of effluent composition and pH that can generally be related to differences in the local microenvironments. Temporal changes such as seasonal fluctuations of precipitation, leading to variations of water infiltration through and runoff over mines and mine dumps, were also observed to noticeably affect effluent composition. These variations have led to a wide range of precipitates, the principal constituents of which are generally one or several of the ferric minerals jarosite, schwertmannite, goethite, ferrihydrite and lepidocrocite.

The present paper consists of two parts: a short review of the genesis and properties of the named minerals, and a study of mine-drainage precipitates formed under different local conditions in various lignite mines and mine dumps of the Sokolov mining district. We show that variations in mine-drainage precipitate mineralogy, such as the presence or absence of specific ‘key’ minerals, can serve as indicators for factors such as the pH and sulphate concentration, and thus — with certain limitations — for the genetic environment during precipitate formation. Such variations in composition are reflected, among other properties, in the precipitate colour, which can therefore be used for a rapid identification and classification — both in the field and by remote sensing — of regions that are potentially prone to acid mine drainage.

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.

Kaolinite deposits, hosted by rhyolitic tuffs, are found in the SE of the ‘Los Menucos’ area (Province of Rio Negro, Argentina). The most representative examples are from the Blanquita and Equivocada mines. To discover the origin of these deposits, a mineralogical, geochemical (major and trace element) and stable isotope study (O and H) of kaolinite was carried out. Mineralogically, Blanquita mine is characterized by the presence of dickite, kaolinite, alunite and pyrophyllite, whereas in Equivocada mine, kaolinite is accompanied by dickite and traces of alunite (without pyrophyllite). The trace element contents and ratios of kaolin samples (P vs. S, Zr vs. Ti, (Cr + Nb) vs. (Ti + Fe), and (Ce + Y + La) vs. (Ba + Sr)) suggest that they formed from the hydrothermal alteration of the enclosing rhyolites although a possible contribution of kaolinite from residual processes cannot be discounted. δ18O values of kaolinite range from +4.8 to +10.3‰, and δD varies from −88 to −116‰. The presence of pyrophyllite in Blanquita mine suggests temperatures of formation >350°C. The calculated isotopic composition of the fluid in equilibrium with kaolinite at 350°C varies from +3.6 to +9.2‰ for O and from −74 to −103‰ for H. These values are compatible with fluids of magmatic origin or with fluids of surficial origin isotopically equilibrated with a rhyolitic magma at high temperatures. The isotope composition of kaolinite from the Blanquita and Equivocada mines is clearly different from kaolinite of residual origin from deposits in the Chubut and Santa Cruz provinces. The isotopic signature has proved to be a useful tool in discriminating between different genetic processes in the formation of kaolin deposits.

K-Ar ages of Eocene glauconite pellets from the Isle of Wight are related to quantified amounts of older glauconite pellets and to occurrences of detrital mica/illite particles that might have been added to synsedimentary pellets during reworking processes. Addition of older glauconite did not significantly bias the K-Ar dates, as the results most often provide the expected stratigraphic reference ages or even significantly lower ages. Alternatively, K-Ar dates significantly greater than those suggested by the stratigraphy appear to result from non-glauconized detrital mica in the pellets which is not always removable, even by high-gradient magnetic separation.

Unexpected ‘old’ K-Ar glauconite ages do not result from misapplication of the method, but from inability to systematically identify and remove the `contaminant' particles from glauconite splits. Analysis of highly evolved glauconite separates is definitely appropriate for reliable isotopic age determinations, but it might not be enough for the final selection, as long-lasting diagenesis might have taken over the synsedimentary process. Much if not all depends on the separation and characterization of the separates, but also on the completion of the glauconitization process which effects cannot always be anticipated.

The fluorine route is thoroughly investigated for the hydrothermal synthesis of montmorillonite in the Na2O-MgO-Al2O3-SiO2-H2O system. Using the optimal conditions suggested by Reinholdt et al. (2001) for the crystallization of pure montmorillonites with the formula Na2x(Al2(1-x)Mg2x☐)Si4O10(OH)2, several parameters (x, Mg content, duration of crystallization, F/Si atomic ratio, pH, nature of counterbalance cation) are varied independently from their ideal values. The products are analysed by various techniques (X-ray diffraction, thermogravimetric analysis-differential thermal analysis, 29Si, 27Al and 19F magic angle spinning-nuclear magnetic resonance). It appears that a pure montmorillonite can only be obtained within a narrow x range (0.10 ≤ x ≤ 0.20). The presence of F in the starting hydrogel and the crystallization time also have significant effects on the purity of the final products. It is shown that a small amount of fluorine is needed for the crystallization of pure montmorillonite phyllosilicates.

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 results of EPR, UV-VIS and IR spectral studies show that benzimidazole forms various complexes with Cu(II) exchanged in the interlayer space of montmorillonite, depending on the acidity of the reaction medium during synthesis. In a nearly neutral solution a bis(benzimidazole)bis(aqua) Cu(II) cationic complex is formed. In a strongly basic solution, benzimidazole is bound to Cu(II) in the form of an anionic bifunctional ligand and a planar intercalated bis(benzimidazolate) Cu(II) complex is formed, where the benzimidazolate anion acts as a bridging ligand in the polymeric complex. The treatment in basic solution leads to partial illitization of the smectite. In a strongly acid solution, a nearly stoichiometric ionic exchange of benzimidazolium ion for Cu(II) ions takes place in the interlayer space of montmorillonite.

The determination of the cation exchange capacity (CEC) of clays by exchange with the cationic copper complexes [Cu(en)2]2+ and [Cu(trien)]2+ is revisited. The procedures reported by Bergaya & Vayer (1997) and Meier & Kahr (1999) are modified slightly. The concentration of the copper complexes in the equilibrium solutions is measured by spectral photometry. Correct CEC values of the [Cu(en)2]2+ exchange are only obtained when a buffer (‘tris’, tris (hydroxymethyl) aminomethane, pH = 8) is added to the equilibrium solution after separation of the clay, because the molar extinction coefficient of this complex depends on the pH of the solution. A standard procedure is recommended as a reference method. In most cases, tris addition is not needed for the determination with [Cu(trien)]2+ cations. Nevertheless, tris addition is recommended in the standard procedure. Determination of CEC for 40 samples (kaolins, ‘common clays’, bentonites, montmorillonites and beidellite) shows a good agreement between measurements using [Cu(en)2]2+ and [Cu(trien)]2+ cations and with results by the ammonium acetate method.

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.

From leaching experiments with metallic uranium-aluminium material test reactor fuel elements in repository-relevant MgCl2-rich salt brines, a Mg-Al-layered double hydroxide with chloride as interlayer anion was identified as a crystalline secondary phase component. In the present study, this Mg-Al-Cl-layered double hydroxide (Mg-Al-Cl-LDH) was synthesized and its ability to adsorb iodine was evaluated. The adsorption of I– was rapid, and equilibrium for an initial concentration of 4.25 x 10-5 mole/l was obtained within 48 h. Further results indicated that the adsorption isotherm for I– retention could be fitted to Freundlich and Dubinin-Radushkevich equations. The values obtained indicate that iodine is adsorbed on Mg-Al-Cl-LDH by an anion- exchange process. The adsorption of I– was also studied as a function of pH. In the pH range between 3.5 and 8.5, the adsorption was independent of the pH. The effects of competiting anions were investigated using an MgCl2-solution instead of water, and indicate that chloride anions have a greater affinity towards the Mg-Al-Cl-layered double hydroxide than iodine.

The chemical and mineralogical compositions, the pore-diameter distribution, and the X-ray diffraction, scanning electron microscopy, thermogravimetric analysis and infrared spectroscopy of kaolin from Suzhou, China, and the physicochemical and catalytic properties of a catalyst prepared from that kaolin, are presented in this paper. Crystallized microspheres (CMR) containing ~30% NaY zeolite can be prepared from the Suzhou kaolin. The catalyst produced performs better than a standard commercial catalyst in terms of activity, attrition resistance, resistance to passivation by Ni and V and better gasoline and coke selectivity.

Clay minerals of calcareous sedimentary rocks of southern Iran, part of the old Tethys area, were investigated in order to determine their origin and distribution, and to reconstruct the palaeoclimate of the area. Chemical analysis, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and thin-section studies were performed on the 16 major sedimentary rocks of the Fars and Kuhgiluyeh Boyerahmad Provinces.

Kaolinite, smectite, chlorite, illite, palygorskite and illite-smectite interstratified minerals were detected in the rocks studied. The results revealed that detrital input is possibly the main source of kaolinite, smectite, chlorite and illite, while in situ neoformation during the Tertiary shallow saline and alkaline environment could be the dominant cause of palygorskite occurrences in the sedimentary rocks.

The presence of a large amount of kaolinite in the Lower Cretaceous sediments and the absence or rare occurrence of chlorite, smectite, palygorskite and illite are in accordance with the warm and humid climate of that period. Smaller amounts of kaolinite and the occurrence of smectite in Upper Cretaceous sediments indicate the gradual shift from warm and humid to more seasonal climate. The occurrence of palygorskite and smectite and the disappearance of kaolinite in the late Palaeocene sediments indicate the increase in aridity which has probably continued to the present time.

The performance of a fluidized cracking catalyst additive prepared from caustic-modified kaolin microspheres for gasoline S reduction was investigated using N2 adsorption, infrared acid-site characterization, X-ray diffraction and small-scale fluid bed reactor tests. The additive exhibited improved coke selectivity and yield distribution, and the S content of cracked gasoline was reduced significantly. The results indicated that a reactive mesoporous structure was formed in the modified kaolin.

The Neogene volcanic region of Cabo de Gata, Almería, SE Spain, is dotted with many outcrops of bentonite, some of them of significant economic interest. The bentonites have their origin in the hydrothermal alteration of pyroclastic rocks (15-7 Ma). The deposits are usually associated with fractures. The major mineral is a dioctahedral Fe- and Mg-smectite (89-75%) and this is accompanied by minor amounts of feldspars, quartz, amphiboles, pyroxenes, biotite, zeolites, disordered tridymite, calcite, etc. This paper describes the geological background, the general characteristics of the bentonites and major aspects of their formation, e.g. type of low-temperature hydrothermal solutions, mass balance, chemical evolutions of the smectites and geochemistry of trace elements. Finally, the characteristics of three of the most important deposits are described.

Clay materials play a key role in determining the retention capacity of a soil, and are widely used in waste treatments. One of the most commonly used clays is palygorskite. The aim of this research is to determine the chemical species formed by Zn when retained in a palygorskitic clay material. Adsorption isotherm analysis is useful in studying the retention process, because it provides a macroscopic view of the retention phenomena. Complementary techniques are needed in order to study the different retention processes. Sorption isotherms of Zn on palygorskitic clay were carried out; the supernatant was analysed by means of dynamic light scattering (DLS) and the residues by using X-ray diffraction (XRD), scanning electron microscopy-energy dispersive angle X-ray (SEM-EDAX)analysis and extended X-ray absorption fine structure (EXAFS). Isotherm analysis shows that the global retention process could be due to the sum of two separate processes, adsorption and surface precipitation via solid-solution. This is supported by DLS, which shows that ζ potential increases as the Zn(II) is retained onto clay surfaces but remains constant during the precipitation process. The XRD pattern corresponding to the Zn-clay system showed weak new peaks, probably from zincite. The microanalysis by X-ray fluorescence of several spots selected for their different electronic densities indicated that the retained Zn was randomly distributed across the clay surface. Analysis by EXAFS supports the hypothesis of retention via adsorption and solid-solution surface precipitation.

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.