The production of pottery in the traditional manner using local raw materials can provide insights into the provenance of ancient artefacts. This study uses mineralogical analysis to evaluate the raw clays and tempers used for pottery production in Zlakusa (western Serbia). Particle-size distribution, plasticity, X-ray fluorescence spectroscopy, X-ray powder diffraction, scanning electron microscopy/energy-dispersive X-ray spectrometry and differential thermal analysis techniques were applied. The mineral phases identified in the raw clay sample are kaolinite/halloysite, mica/illite, smectite, quartz, paragonite, feldspar, calcite and hematite. The clay body sample is a mixture of raw clay and crushed calcite in a ~50:50 ratio, which was confirmed using various techniques. We have also considered and investigated the technological potential of the sampled materials, taking into consideration their actual and potential applications. It was confirmed that the clay body may be used in the manufacture of bricks and pottery, but its industrial application is limited by the paste recipe.

Newly discovered K-bentonite beds, interstratified with limestones/dolomitic limestones of the Upper Devonian–Lower Carboniferous Yılanlı Formation, are exposed in the northwestern Black Sea region of Turkey, around Zonguldak and Bartın. K-bentonite samples collected from four different locations: the Gavurpınarı and Yılanlı Burnu quarries from the Bartın area, the Çimşir Çukurları quarry from the Şapça area, and the Güdüllü and Gökgöl highway tunnel section near Zonguldak city were investigated using optical microscopy, X-ray diffraction and inductively coupled plasma mass spectrometry in order to reveal their mineralogical and geochemical characteristics and understand their origin and evolution. The K-bentonites occur at different levels in the Yılanlı Formation as 2–40 cm-thick, greenish to yellowish beds cropping out several hundred metres along strike. Preliminary biostratigraphic data suggest that the protoliths of the Bartın (Gavurpınarı and Yılanlı Burnu) and Güdüllü K-bentonites were deposited at around the boundary between the Frasnian and Famennian, whereas those in the Şapça and Gökgöl sections are slightly younger (Devonian–Carboniferous boundary interval). The lithofacies types of the host carbonate rocks suggest an ‘epeiric’ shallow carbonate platform environment. Illite and mixed-layer illite-smectite were the major clay minerals in the K-bentonites. The K-bentonites from the Bartın area display a high degree of illitization and consist mainly of illite indicating high-grade diagenesis, whereas illite-smectite-rich samples from the Şapca and Gökgöl tunnel locations reflect relatively lower diagenetic conditions. According to their geochemical compositions, two groups of K-bentonites were distinguished, one with alkali basalt (Bartın area and Güdüllü locations) and one with trachyte affinities (Gökgöl tunnel and Şapça locations). Geochemical fingerprinting of K-bentonites by trace and rare earth element (REE) data suggest that tephras with alkali basalt composition have been derived by a source formed in a ‘continental back-arc’ setting, whereas the source of K-bentonites with trachytic precursors is related to ‘continental within-plate rifting’. An evaluation of the global Late Devonian and Devonian–Carboniferous volcanism suggests that the bentonite precursors may be related to late-Variscan magmatism in Laurussia.

Greece is a major bentonite producer, with Milos Island being one of the largest bentonite mining centres in the world. In addition to the bentonite deposits which are well known, various other occurrences exist in the islands of Chios and Samos, Eastern Aegean and in some areas of Thrace, in NE Greece. These bentonites are associated with volcanic activity and their age ranges from Lower Oligocene in Thrace, to Lower–Middle Miocene in Chios and to Upper Miocene in Samos. Although some of these materials have been utilized since ancient times (e.g. the Samian Earth), these bentonites have been mined only at a local scale. In this study the first data on the mineralogical and geochemical characteristics of these bentonites are presented.

The Samos bentonites of UpperMiocene age are medium–lowgrade (40–70% smectite) and crop out in the SE margin of the Karlovasi Basin formed at the expense of acidic pyroclastic flows mainly in a subaeriallacustrine environment. They consist mainly of Ca-rich medium–high-charge montmorillonite, opal-CT and sanidine with minor quartz and locallymordenite. The Chios bentonites of Lower–MiddleMiocene agewere formed at the expense of trachyandesitic tuffs in a lacustrine environment in the Neogene Basin at theSEpart of the island. They consist mainly of Ca,Mg-rich high-charge montmorillonite (33–75%), similar to the SAz-1, and opal-CT, minor plagioclase, chlorite, plagioclase, carbonates and traces of talc and serpentine. In Thrace, LowerOligocene pyroclastic flows, tuffs and lavas of acidic-intermediate compositionwere altered to zeolites and bentonites in the sedimentary basins of the Feres-Pefka, Skaloma and Sappes areas. The parent pyroclastic rockswere altered to Ca-rich and in places,Na-rich, dioctahedralmontmorillonite or Fe-rich beidellite (Sappes area) and with minor opal-CT,mordenite, quartz, plagioclase and, in places, illite. The bentonites are medium–high grade (50–58% smectite in Feres-Pefka, 74–86% in Skaloma and 29–40% in Sappes).

The bentonites havemoderate cation exchange capacity andmoderate/lowswelling index and viscosity and they are not suitable for the drilling and foundry industries. However, preliminary results show that after processing, most of the depositsmight be utilized in high added-value applications such as bleaching earths or in the synthesis of clay-based polymer nanocomposites.

Highly alkaline environments induced by cementitious materials in radioactive waste repositories are likely to alter montmorillonite, the main constituent of bentonite buffer materials, and are likely to cause the physical and/or chemical properties of the buffer materials to deteriorate. The deterioration may cause variation in hydraulic conductivity of the buffer. However, empirical data on the variation of hydraulic conductivity are scarce, mainly because the alteration of compacted buffer materials, sand-bentonite mixtures, is extremely slow. In this study, laboratory experiments were performed to observe changes in hydraulic conductivity of sand-bentonite mixtures, accompanied by their alkaline alteration, using NaOH-based solutions at 80–90°C. Series-1 multi-step alteration/water conduction experiments resulted in an increase in the hydraulic conductivity by one order of magnitude over a 200 day period. Series-2 single step alteration/water conduction experiments revealed a decrease in the montmorillonite contents with time and a resulting increase in the hydraulic conductivity by 30 times over the 67 day period. Series-3 simultaneous alteration/water conduction experiment also demonstrated an increase in the hydraulic conductivity by 30 times over the 150 day period. The results proved that the alkaline alteration of the bentonite buffer can increase the hydraulic conductivity. The data obtained in this study are useful for verification of the code that will be used for assessing the alteration.

Fuchsite and other Cr-rich phyllosilicates, paragenetic with dolomite, are present in some ultramafic enclaves from the ‘frailesca’ rock (a lapilli- to block-size pyroclastic lithic-tuff), in the Almadén mercury mining district, Spain. Analyses (EMPA and TEM) of fuchsite and Cr-chlorite showed a relatively large range in levels of Cr2O3. Petrographic relationships between these phyllosilicates and primary relics of Cr-spinel crystals, as well as their high Cr content, indicate that these Cr-rich minerals originated from primary chromian spinels through an early hydrothermal alteration stage. The hydrothermal fluids accounting for this early alteration would be of relatively high temperature, high aCO2 and aK, and variable aNa/K. In a later alteration stage, fuchsite was partially or totally replaced by illite and Cr-illite, giving rise to an argillitic alteration.

The firing transformations of a Triassic calcareous clay were investigated, in the range 800 –1075ºC, by using X-ray diffraction and by measuring some ceramic properties (linear shrinkage, density and porosity). It was found that gehlenite and wollastonite are the only neoformed crystalline phases, when anorthite is also expected. The occurrence of these phases is discussed, emphasizing the role of the activity of free silica and calcite concentration. Moreover, new reaction paths for anorthite and wollastonite are envisaged.

The Tertiary sediments of the southern part of Almazán basin (Province of Soria) exhibit two different facies with a sharp transition between them: (1) a coarse detrital facies; and (2) a lutite and carbonate facies. The vertical evolution of these facies in the different sections and boreholes is made up of several retrograde depositional sequences which evolve from proximal alluvial fans to carbonate lacustrine systems associated with the most distal fan sediments.

The variation of the mineralogical association (carbonates, quartz, detrital clay minerals, palygorskite and, occasionally, sepiolite and smectites) allows four ‘mineralogical facies’ to be established. Each facies has a distinctive mineralogy related to the main genetic processes: (1) detrital facies; (2) transitional facies; (3) ‘chemical dolomite-palygorskite’ facies and (4) ‘chemical calcite’ facies. Although the carbonates (calcite and dolomite) are always the most abundant minerals, fibrous clay minerals are also important. The main mechanism of mineral authigenesis in this basin is chemical precipitation; the presence and distribution of carbonates and fibrous clay minerals is controlled by the relative concentrations of [Mg2+], [Ca2+], pCO2, pH and [SiO4H4]. Palygorskite occurrences, in these conditions, are related to dissolution-precipitation mechanisms of pre-existing detrital material.

In the Upper Cretaceous-Danian North Sea chalk, silica composed of nano-size quartz spheres is dispersed in the chalk matrix, and quartz is present in bands and nodules of flint. In the present investigation of the North Sea Danian chalk the nano-quartz in the chalk matrix is compared with the silica in the flint. Samples of chalk and flint layers from four North Sea wells have been investigated. Atomic Force Microscopy (AFM) has been applied to image the quartz in the chalk and in the flint. X-ray diffraction (XRD), including analysis of the positions and profiles of hkl reflections in powder diffraction patterns, has been applied to characterize the lattice of the quartz in both the chalk matrix and in the flint. The quartz in the chalk matrix and in the flint is composed of nano-quartz spheres having identical cell parameters. Based on the results we propose a new model for formation of flint in North Sea chalk: (1) The nano-quartz in the flint, like the nano-quartz in the chalk matrix, has crystallized in the marine Chalk Sea environment. The colloidal quartz particles flocculated and were deposited on the sea floor mixed with calcitic bioclastic material. (2) Regional variations in the concentration of nano-quartz particles in the sediment reflect different degrees of acidification of the Chalk Sea. (3) This resulted in areas where practically all the calcite bioclasts were dissolved leaving a high concentration of nano-quartz particles to form flint layers; where there was less dissolution, indurated chalk with abundant nano-quartz particles is now preserved. (4) The acidification could have been caused by the effects of enhanced atmospheric CO2 linked to massive short-lived volcanic eruptions in the British Tertiary Igneous Province.

Bentonite is a potential material for use in the engineered barrier of radioactive waste repositories because of its low hydraulic permeability, self-sealing capability and retention capacity. It is expected that bentonite would react at the elevated temperatures accompanying the radioactive decay in the nuclear waste. The presented study was started in order to improve understanding of the coupled influence of temperature and (pore) water on the physicochemical and mineralogical properties of bentonite during thermal treatment under near-field relevant conditions. Granular Na-bentonite MX-80 was differently saturated (Sr = 1–0.05) and stored at different temperatures (50–150°C) in a closed system. Upon dismantling after different periods of time (3 to 18 months), mineralogical characteristics, cation exchange capacity and content of leachable cations, as well as physicochemical properties such as surface area and water adsorption were investigated.

The results showed a high mineralogical stability. A slight conversion from the sodium to an earth alkali form of the bentonite was observed. However, considerable changes in the physicochemical properties of the bentonite were observed, particularly by treatment above the critical temperature of 120°C. The cation exchange capacity decreased during heating at 150°C by approximately. 10%. The specific surface area dropped by more than 50%. The water uptake capacity under free swelling conditions showed a slight tendency to lower values especially for samples heated for more than 12 months. The water vapour adsorption ability in contrast drops by 25% already within three months at T = 120°C. These changes are mostly related to the variations in the interlayer cation composition and to smectite aggregation processes. The observed alterations are rather subtle. However, temperatures ⩾ 120°C had a remarkable negative influence on different properties of MX-80.

Alkali activation with sodium carbonates is a traditional method to improve bentonite properties for a variety of applications. In some applications, natural sodium-rich bentonites are preferred, and custom regulations require proper declaration of Na-rich bentonites, with respect to activation. Consequently, there is need for a method that can unambiguously distinguish between natural and activated Na-rich bentonites.

The paper deals with the preparation of several alkali-activated sets, specifically (a) anhydrous Na2CO3 with trace amounts of thermonatrite (Na2CO3.H2O) and trona (Na3(CO3)(HCO3).2H2O), hereafter called ASC, (b) mixtures of ASC with CaCO3, and (c) mixtures of ASC with CaCO3 and a Ca2+-rich bentonite at different moisture contents, to distinguish natural and alkali-activated bentonites by simultaneous thermal analysis (STA) linked with a mass spectrometer for the analysis of evolved gases. STA linked with MS revealed alkali activation of bentonites, even in the presence of CaCO3. The moisture content during activation and storage of activated samples, however, has a strong influence on the detection of activated samples by STA-MS. Uncertainties remain with respect to unknown foreign phase contents of technical ASC used for alkali activation in practice and the influence of carbonates like dolomite or siderite, which are often present in natural bentonites.

The spatial arrangement of platy particles in a clay is defined by an orientation ratio which can be derived analytically from optical birefringence as well as from X-ray diffraction data. Measurements on kaolin slurries consolidated by increasing loads were used to verify that orientation ratios obtained experimentally by these two methods are in fact equivalent. In contrast it was found that particle orientation cannot be assessed objectively from electronmicrographs alone. A combined optical-X-ray study of two natural clays (London Clay and Lias Clay) revealed that the kaolinite crystals are oriented only slightly more than the illite crystals, and showed that the correspondence between optical and X-ray measurements is also valid for natural clays.

Two phlogopites depleted of potassium by extraction with sodium tetraphenyl boron released resorbed potassium more readily than the original micas, but the large difference in the exchange parameters of the two micas were paralleled by those of their potassium-saturated alteration products. The apparent basal spacings of the potassium-saturated alteration products were about 0·03Å larger than those of the corresponding untreated micas; their broader lines indicate structural irregularities.

A kaolin mineral in the form of long fibres, similar to the fibrous kaolin from Brazil (de Souza Santos et al., 1965), was found in the <2 μm fraction of an Ekiti series soil formed on biotite gneiss at the International Institute of Tropical Agriculture, Ibadan, Nigeria. The fibres, up to 6 µm long, appear tubular in electron micrographs. Scanning electron micrographs show that the mineral is formed by direct weathering of ort oclase and, perhaps, biotite.

Bastnaesite occurs in the < 2 µm fraction of the same weathering gneiss but not in the coarser fractions or the overlying soil. It was identified by indexing the X-ray powder pattern of a concentrate obtained by treating the clay with HF. The unit cell thus found as hexagonal with a = 7·056 and c = 9·730 Å, and was confirmed by electron diffraction from selected grains. Evidence of chemical composition was obtained by XRF and IR spectrometry. Bastnaesite can be mistaken for gibbsite because their strongest reflections have nearly the same spacing, d = 4·85 Å, when unheated oriented specimens are used. The occurrence of bastnaesite indicates that it is formed when the rock weathers, but is unstable in the soil.

Diagenetic chlorite is forming as a result of temperature-controlled burial diagenesis in shales from the Sleipner area of the North Sea. Accompanying chlorite diagenesis, kaolinite and illite-smectite decrease in abundance, and illite increases in abundance. These clay mineral transformations occur between 122–126°C at temperatures higher than normally expected for chlorite diagenesis. Kaolinite and ordered illite-smectite are largely unaffected by diagenesis below 100°C. It is proposed that chlorite diagenesis is thus delayed due to the absence of a source of ions resulting from smectite decomposition. Clay mineralogy is of no lithostratigraphic use in the Jurassic sediments of the Sleipner area. However, the zone of chlorite diagenesis is a reliable indicator of maximum burial temperature.

Three steps have been established during the Holocene formation of the bar-built estuary of Las Nuevas (Doñana National Park, Spain), on the basis of the clay mineralogy variations and the palaeontological record. The first step is characterized by the presence of ostracodes and homogeneous quantities of clay minerals (17–20% illite, 25–29% smectites), values of smectite (0.64–0.70) and illite (0.60–0.70) crystallinity indexes, and the ratio of AlVI/(FeVI + MgVI) in illite (0.46–0.47). This zone is interpreted as a very shallow lagoon with euryhaline conditions. The presence of roots, the progressive disappearance of foraminifers and an increase in the smectite content (up to 35%) define the second step. A salt-marsh environment with low-energy hydrodynamic conditions is deduced for this zone. The third step is characterized by an increase in illite content (up to 35%), and a decrease of the smectite content (up to 21%). The smectite crystallinity index decreased to 0.38, whereas the illite ratio AlVI/(FeVI + MgVI) decreased to 0.36. In this zone, the ostracode assemblage contains numerous juvenile stages of coastal species coinciding with lumachelle accumulations of the estuarine bivalves, abundant foraminifers and the presence of charophytes. This zone represents a strong marine input, probably caused by storms.

Self-diffusion coefficients of water molecules (1H2O) in Na-stevensite gel were measured by pulsed-gradient spin-echo (PGSE) proton nuclear magnetic resonance (NMR). The effects of clay fraction (0.00 37.7 wt.%) and temperature (20.0 60.3°C) were studied. The results show: (1) phenomenologically, the H2O self-diffusivity in the clay gel, D, is expressed by D/D0 = exp( 0.0198w) where D0 is the H2O self-diffusivity in bulk water of the temperature and wis the clay weight fraction (wt.%). (2) The activation energy of the diffusivity in the stevensite gel is nearly equal to that in bulk water. Thus, the normalized diffusivity, D/D0, obeys a temperature-independent master curve. (3) The exponential dependence of D/D0 on wfor w <25 wt.% (≈ 12 vol.%) can be explained by a random walk model, in which unbound H2O molecules diffuse in the geometrically tortuous pore structure of randomly scattered clay mineral grains. (4) The measured diffusivity can also be explained by a model of unbound H2O diffusing in a polymer network with a specific meshsize or characteristic interval of the crosslinkage.

Stevensite has been found at Dean Quarry, The Lizard, Cornwall, associated intimately with the disordered, hydrated variety of talc known as kerolite. Both minerals occur as pseudomorphs after pectolite and as microcrystalline anhedral masses filling cavities and veins in gabbro. Associated minerals include calcite and prehnite. The XRD data show that stevensite occurs as a physical mixture with kerolite, rather than as mixed-layer stevensite-kerolite. Kerolite is unaffected by glycerol treatment whilst stevensite readily expands: this test provides the only reliable distinction between the two minerals. Differences in IR and chemical data for stevensite and kerolite are subtle; data are broadly similar to those in the literature. Both minerals are readily decomposed to amorphous silica by hot concentrated HCl. Stevensite dehydroxylated at 400°C for 1.5 h is virtually indistinguishable from kerolite. The Dean Quarry occurrence is similar to many others worldwide. Stevensite and kerolite formed after prehnite, calcite, analcime, pectolite and natrolite during a phase of decomposition and alteration of these earlier minerals. ‘Stevensite’ from the first British occurrence in the Whin Sill, North Tyne, has been re-examined and appears to be kerolite or ‘hydrated-talc’.

Pigments similar to the famous Maya Blue were prepared by entrapment of indigo inside the channels of natural zeolites such as clinoptilolite and mordenite. The zeolites were mixed and ground with indigo and then heated at 150°C. Surplus (unbound) dye was removed by solvent extraction or by vacuum sublimation. As is the case when synthetic zeolites are used as matrices, the colouration of the resulting pigments could be modified by the previous cation exchange of the zeolite.