Seven samples, representative of all zones of the Upper Chalk in the Arundel area of Sussex, were treated with acetic acid and the residues analysed to determine their mechanical and mineralogical compositions. The sand and silt fractions of the residues consist mainly of flint and opaline silica, collophane, limonite, and quartz, and the clay fractions consist of montmorillonite, mica, quartz, and apatite. Authigenic apatite and quartz occur in the clay and silt and authigenic alkali feldspar in the silt. The montmorillonite may also be authigenic.

The alteration and transformation behaviour of montmorillonite (Wyoming bentonite) was studied experimentally to simulate the mineralogical and chemical reaction of clays in contact with steel in a nuclear waste repository. Batch experiments were conducted at 80 and 300ºC, in low-salinity solutions (NaCl, CaCl2) and in the presence or otherwise of magnetite and hematite, over a period of 9 months. The mineralogical and chemical evolution of the clays was studied by XRD, SEM, transmission Mössbauer spectroscopy and EDS-TEM. Experimental solutions were characterized by ICP-AES and ICP-MS. The main results are that no significant change in the crystal chemistry of the montmorillonite occurred at 80ºC, while at 300ºC, the presence of Fe oxides leads to a partial replacement of montmorillonite by high-charge trioctahedral Fe2+-rich smectite (saponite-like) together with the formation of feldspars, quartz and zeolites.

The impact of diagenetic processes on petroleum entrapment and recovery efficiency has focused the vast majority of the world's conventional oil and gas resources into relatively narrow thermal intervals, which we call Earth's energy “Golden Zone”. Two key mineralogical research breakthroughs, mainly from the North Sea, underpinned this discovery. The first is the fundamental particle theory of clay mineralogy, which showed the importance of dissolution/precipitation mechanisms in the formation of diagenetic illitic clays with increasing depth and temperature. The second is the surface area precipitation-rate-controlled models for the formation of diagenetic cements, primarily quartz, in reservoirs. Understanding the impacts of these geological processes on permeability evolution, porosity loss, overpressure development, and fluid migration in the subsurface, lead to the realization that exploration and production risks are exponential functions of reservoir temperature. Global compilations of oil/gas reserves relative to reservoir temperature, including the US Gulf Coast, have verified the “Golden Zone” concept, as well as stimulated further research to determine in greater detail the geological/mineralogical controls on petroleum migration and entrapment efficiency within the Earth's sedimentary basins.

The nickel arsenate KNiAsO4 has a mica-like layer structure with surface charge densities similar to brittle micas. In contrast to micas it easily exchanges alkylammonium ions. The interlayers have paraffin-type chain arrangements, as in alkylammonium vermiculites and alkylamine smectites and vermiculites, but the very regular chain packing causes a marked odd/even alternation of the basal spacings. The reactions of KNiAsO4 throw light on the exchange behaviour of micas.

The results obtained from this study of kaolinite dehydroxylation explain why different investigators have ascribed both first-order kinetics and a diffusion mechanism to this reaction. The fact that activation energies reported by these workers agree well, in spite of the different kinetics assumed when performing the calculations, is also explained. From a comparison of the results obtained by isothermal and non-isothermal methods it is concluded that, for reacted fractions, α, <0·6, kaolinite dehydroxylation is controlled by a diffusion process. A reaction mechanism explaining this behaviour is proposed.

Analysis of the distribution of gibbsite in soils and saprolites of Galicia, NW Spain, leads to the conclusion that this mineral is mostly formed by inorganic mechanisms in open, well-drained and desaturated systems in the initial stages of weathering of various aluminosilicates, especially plagioclases. No evidence has been found to support the hypothesis that it is a feature inherited from hotter climates, as it has not been identified to date either in ancient sediments or in the most evolved and weathered soils. The role of organic matter and the possibility ofa biogeochemical origin is also discussed: it is considered that this mechanism is only important during podsolic soil development.

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.

There is increasing research interest in potential applications of halloysite as fillers for polymer composites, controlled drug delivery, carriers for the supply and sustained release of active agents for anticorrosion coatings, in nanoreactors or nanotemplates, and for the uptake of contaminants or pollutants and support for catalysts. In this review, recent findings in terms of the prospects and challenges of using halloysite nanotubes (HNTs) in different polymeric matrices targeting a range of old and new applications are discussed and evaluated. The compositions include chitosan/halloysite membranes as bone-tissue scaffolds, polylactic acid (PLA)/halloysite membranes for food-packaging applications and their antimicrobial activities, instrumented impact properties of epoxy/halloysite nanocomposites and the role of halloysite in the self-healing of epoxy composites, polyacryronitrile (PAN)/halloysite membranes for use in water filtration as well as a review of some recent applications of halloysite/alginate beads in the adsorption of contaminants such as lead.

: Smectite genesis in two granitic saprolites was studied, using qualitative and quantitative mineralogical methods and high resolution transmission electron microscopy (HRTEM). The primary minerals (plagioclase and mica) give rise to the formation of different kinds of smectites according to the weathering conditions (pH and drainage). Under a relatively basic, drained environment, a neoformed montmorillonite with a spheroidal organization exists in fillings of plagioclase cores. In the same conditions biotites are transformed into beidellites with a quasi-crystal organization. Under hydromorphic conditions, muscovites evolve incompletely towards smectites, whereas biotites lead to a montmorillonite with a tactoid organization.

This work describes the development of potential multi-element slow-release fertilizers obtained by mechanochemical activation of mixtures of kaolinite and ammonium or potassium monohydrogen phosphates. Preliminary results of talc amorphization have also been included. The methodology consists of milling the materials in a high-energy ball mill, where the influence of rotation and time of milling were investigated. The samples were characterized by XRD, FTIR, TGA/DTA, SEM and MAS-NMR. The experimental results explain the slow-release behaviour of the amorphous nanostructured materials in aqueous suspensions, especially the MASNMR spectra, which showed the changes in the chemical environment of the elements analysed. The materials displayed slow-release behaviour for phosphates probably because the aluminium ions in the mineral structure interact more thoroughly with phosphate than potassium or ammonium. Nevertheless, in general, all of the nutrients were released slowly.

Six clays from volcanic ash soils at different stages of weathering differ in their relative halloysite content with respect to kaolinite and several surface properties, namely CEC, and exchange selectivity for K+. These three parameters are related to each other in that they all decrease with increasing soil weathering stage. XRD data show that the hydrated 1:1 layer-silicates in these clays combine with smectite to form interstratified H/Sm clay minerals. In these mixed-layers, the content and layer charge of smectitic units decrease as the relative halloysite content in the clay decreases. These clays thus depict a weathering sequence that is parallel to the weathering sequence of the soils from which they originate. It is also shown that the smectites in the H/Sm minerals have the distinctive composition and ESR spectrum of Fe-rich 2:1 clay minerals belonging to the beidellite-nontronite series. The information obtained explains why these clays have high CEC and distinct affinities for K+. It is hoped that this study will help to clarify the controversy concerning the CEC and related surface properties attributed to hydrated halloysite.

The kaolinite from Albian sedimentary deposits (Escucha and Utrillas Formations) of the Iberian Range (Spain) have been investigated. This research has shown the presence of different types of kaolinites (detrital and diagenetic) along with micaceous phases in these deposits. Detrital kaolinites show anhedral morphology, low crystallinity and a degree of ordering as well as the presence of interstratified smectite layers. They constitute the matrix of the claystones and siltstones and were probably formed as a consequence of intense weathering processes in the source area during the warm period of the early Cretaceous. Diagenetic kaolinites have been recognized in the sandstones and siltstones, with kaolinite growing between ‘expanded’ mica flakes and vermiform and euhedral kaolinite forming the matrix. They have euhedral morphologies, high crystallinity and a high degree of ordering. They grew in situ as a response to incipient diagenesis by K-feldspar dissolution and/or organic acid-rich fluids derived from the maturation of organic matter in shales.

The Tinto river is one of the most polluted stream environments in the world, as a result of both acid mine drainage and natural acid rock drainage. Two representative samples from the phyllosilicate-rich rocks exposed in the drainage basin (Palaeozoic chlorite-bearing slates and Miocene smectite-rich marls) were treated with acid river water (pH = 2.2) for different times to constrain the effects of extreme hydrogeochemical conditions on clay mineral stability. Illite and kaolinite did not show appreciable variations in their crystal chemistry parameters upon treatment. Chlorite underwent an incipient chemical degradation evidenced by the progressive loss of Fe in octahedral positions coupled with a shortening of the b unit-cell parameter, although no weathering products of chlorite were observed. Smectite and calcite were rapidly and fully dissolved thus neutralizing the water acidity, and subsequently Fe and Al oxy-hydroxides and opaline silica precipitated from the aqueous solution, together with a neoformed amorphous silicate phase largely enriched in Al and Mg.

The verdine facies, previously confused with components of ancient ironstones, has been studied in relation to its distribution, mineralogy, genesis, environment, and geological significance. Several chemically specific components are present including (i) a ferric and magnesian dioctahedral-trioctahedral 1 : 1 clay mineral, (ii) a chemically equivalent chlorite, (iii) a component intermediate between smectite and swelling chlorite, and (iv) a problematic low-temperature pyrophyllite-like clay mineral. The genetic mechanism is a series of crystallogenetic reactions using cations from the previous phase; this model, where a mineral phase is shown to be a temporary state of arrangement of cations, suggests that authigenic “marine” minerals may reflect diagenetic geochemical factors different from those in the original sea.

Sepiolite is an Mg-silicate with fibrous morphology. Its structure consists of talc-like ribbons parallel to the fibre axis. Although the tetrahedral sheets are continuous, the apices in adjacent ribbons point in opposite directions, each ribbon alternating with an open channel along the fibre axis. Tetrahedral positions are normally filled with Si atoms. The width of the ribbons corresponds to eight octahedral positions, which are, normally occupied by Mg atoms, and the channel cross-section is 3·8 x 9·4 Å. This structure gives the mineral a high adsorptive capacity and molecular sieve capability. The ideal mineralogical formula is (OH2)4(OH)4Mg8Si12O30.8H2O (Brauner & Preisinger, 1956).

Activation of sepiolite by acid attack has been extensively studied (Fernández-Alvarez, 1972; Jiménez-López et al., 1978; Rodríguez-Reinoso et al., 1981). This note describes the changes undergone by sepiolite during dissolution of the octahedral Mg-sheet by HCl attack, silica gel being the end-product. This process was followed by IR spectroscopy, study of Mg-extraction kinetics, and morphological observations by SEM and TEM.

Nickel crystal chemistry was systematically studied in various phyllosilicates, mainly the natural phases selected from the ‘garnierites’ of the supergene ore deposits of New Caledonia. Minerals which do not usually occur in New Caledonian parageneses were synthesised, as they could represent intermediate phases of genetic importance. In the kerolite-pimelite series, a linear relationship occurred between the ratio I(13,20)/I(02,11) of the hk bands and Ni-content. Diffuse reflectance spectra were used to derive the crystal chemical parameters of Ni. These confirmed its divalent character and its occupation of octahedral sites; the resulting structural distortion was slight and could not be detected in some minerals. There was no optical evidence for Ni atoms in 4-fold coordination. The two main parameters which showed significant variations among the studied phases were site distortion and crystal field stabilization energy (CFSE). Site distortion was at a maximum in trioctahedral smectites and sepiolite. CFSE depended on the mineralogy, crystallinity and chemical composition (Al-content) of the phase. Finally, clay minerals are classified according to the increasing stability of Ni in the octahedral sheet, which has been tentatively related to the geochemical distribution of this element. Secondary minerals are usually enriched vs. primary ones and among them are nepouite and kerolite which exhibit a high CFSE in contrast to sepiolite.

The Bridport Sands is a widespread marine sandstone of Lower Jurassic age found in much of southern England. It is a very fine grained, moderately sorted quartz-arenite and is characterized by the alternation of friable and hard calcareous-cemented layers. The sands form the upper reservoir in the Wytch Farm Field, Dorset, which is currently producing at the rate of around 4000 barrels per day. Investigation of core material to assess the suitability of water injection for gas/oil recovery has shown that significant reductions of liquid permeability compared to air permeability occur. These reductions vary from 30% or less in the best quality reservoir to more than 70% in low-permeability sandstones. Clay minerals in the Bridport Sands comprise mainly kaolinite and mixed-layer clays of both the illite-chlorite and illite-smectite types. Small amounts of vermiculite and chlorite also occur. The kaolinite is found as loosely-attached, discrete particles, whilst the mixed-layer clays form patchy pore linings. The permeability reductions may be explained by: (i) the adsorption of water and expansion of poorly-crystalline mixed-layer illite-smectites causing blockage of pore space (this reduction is largely reversible) and (ii) the physical movement of authigenic kaolinite crystal aggregates blocking pore-throats (this reduction is largely non-reversible). The pore-size distribution, clay particle sizes, the distribution of the clays within the pore space, and the composition of the clays are all important factors in controlling porosity/permeability relationships and permeability reductions in the friable reservoir intervals in the Bridport Sands.

The Boom Clay Formation of early Oligocene age, which occurs underground in northern Belgium, has been studied intensively for decades as a potential host rock for the disposal of nuclear waste. The goal of the present study is to determine a reference composition for the Boom Clay using both literature methods and methods developed during this work. The study was carried out on 20 samples, representative of the lithological variability of the formation. The bulk-rock composition was obtained by X-ray diffraction using a combined full-pattern summation and singlepeak quantification method. Siliciclastics vary from 27 to 72 wt.%, clay minerals with 25–71 wt.% micas, 0–4 wt.% carbonates, 2–4 wt.% accessory minerals (mainly pyrite and anatase) and 0.5–3.5 wt.% organic matter. This bulk-rock composition was validated independently by majorelement chemical analysis. The detailed composition of the clay-sized fraction was determined by modelling of the oriented X-ray diffraction patterns, using a larger sigma star (σ*) value for discrete smectite than for the other clay minerals. The <2 μm clay mineralogy of the Boom Clay is qualitatively homogeneous; it contains 14–25 wt.% illite, 19–39 wt.% smectite, 19–42 wt.% randomly interstratified illite-smectite with about 65% illite layers, 5–12 wt.% kaolinite, 4–17 wt.% randomly interstratified kaolinite-smectite and 2–7 wt.% chloritic minerals (chlorite, “defective” chlorite and interstratified chlorite-smectite). All modelled clay mineral proportions were verified independently using major-element chemistry and cation exchange capacity measurements. Bulkrock and clay mineral analysis results were combined to obtain the overall detailed quantitative composition of the Boom Clay Formation.

Structural features of very highly disordered 2:1 trioctahedral phyllosilicates from the Madrid Basin have been studied. Application of Fourier methods to XRD patterns shows that these materials consist of random kerolite-stevensite mixed-layered phases (R = 0) with 50–80% kerolite layers, and have a very small particle size with a mean of three unit-cells stacked in the c* direction. IR spectrum deconvolution in OH-stretching and librational modes seems to indicate five different types of water. Specific surface measurements (N2, BET) indicate anomalous high values (240–320 m2/g). These results suggest important catalytic and surface chemistry applications.

The surface composition of some halloysites with different particle morphology has been investigated by X-ray photoelectron spectroscopy (XPS) before and after removal of external Fe. The Fe(III) 2p3/2 binding energy of external Fe is appreciably smaller than that of structural Fe. Particle morphology is influenced by structural Fe content. The long-tubular halloysite has very little surface Fe, and its concentration tends to increase with the proportion of non-tubular particles in the samples. The spheroidal sample contains the most structural Fe which, however, does not appear to influence particle shape directly. Study by XPS indicates that Fe substitutes for Al in octahedral positions in approximately 1 : 2 proportion. As a result, an increase in octahedral vacancies and cation exchange capacity would be predicted. Further, halloysite layers within a crystal are generally inhomogeneous in composition. Built up like “onion skins”, the surface layers would either be enriched or depleted in Fe depending on the chemical environment in which crystal growth occurs.