Millimetre-sized flakes of a homogeneous, high layer charge vermiculite from S. Olalla (Spain) saturated with l'ornithine cations were made to swell in l'ornithine hydrochloride solutions of various concentrations, and the gel-like structures formed were subjected to uniaxial loads up to 150 g/cm2. Small-angle X-ray diffraction measurements from the swollen flakes show well-modulated intensity patterns from which the equilibrium interlayer distances were obtained for the various swelling conditions. The interlayer spacings can be adequately expressed as normal-logarithmic distribution functions of probability density. The gel texture is described in terms of the average number of elementary layers, all in parallel orientation, constituting independent coherent domains within the swollen flake. Changes in structure and in texture taking place as the gel volume increases, or as water is expelled from the interlayer volume under mechanical compression, are followed by the variation of the corresponding parameters of order.

Four ice advances have been recognised in East Anglia but only two of these, the Lowestoft and the Gipping, have deposited till in the Cambridge area. The clay fractions of these tills have been investigated and compared with those of the Oxford, Ampthill, Kimeridge and Gault Clays, the Lower Greensand and the Chalk, all of which outcrop in the district and could be expected to contribute material to the tills.

The value of clay mineralogical analysis as a means of measuring directions of ice-movement is critically discussed.

An outline account is given of the more important processes of weathering and soil-formation which occur on the Gipping till in the Breckland area.

The dominant source of oxalate-soluble Al in the B horizon of a brown podzolic soil developed on andesite appears to be hydroxyaluminium interlayers in a dioctahedral vermiculite in the clay and silt fractions, of which the latter contributes most to the total extractable Al and fluoride reactivity of the whole soil. Cold sodium carbonate solutions extract as much interlayer Al as does oxalate, indicating that this fraction of the interlayer material is highly reactive, and sharply distinguished from more resistant interlayers which are also present.

Clay minerals are almost ubiquitous in soil and rock and are among the most reactive silicates. They affect the engineering behaviour of soil and rock both as materials of construction and as foundation materials. In the petroleum industry, clay affects the permeability of reservoir formations, it is a common cap-rock, and it is also a constituent of the fluids used in drilling operations. Engineering behaviour almost always involves clay-water interaction and in turn this depends on the nature of water and solutions and on the composition and microstructure of the clay. The importance of clay to specific problems from each of these areas is discussed. In foundation engineering its role in soil-moisture interaction is illustrated by reference to problems resulting from the geological history of some North American soils and from engineering activities. In building materials, reference is made to its effect on concrete durability in aggregate-related problems. The importance of clay in petroleum engineering refers to authigenic clays in reservoir rocks, to clay behaviour in the Alberta oil sands and to the use of clay minerals as a geothermal thermometer.

This review summarizes several aspects of the interactions between organic dyes and clay minerals, and presents some interesting properties of hybrid materials based on these components. It explains the basic phenomena and photophysical properties of dye/clay mineral hybrid systems (DCHS) while examining the role of clay minerals in them. A brief history of using dyes as tools for clay research and on traditional materials based on DCHS is presented. Metachromasy, the phenomenon of colour change related to the formation of dye molecular aggregates is described in detail and analysed from various perspectives. The properties of DCHS, including photoactivity, luminescence, photocatalytic properties, optical anisotropy and non-linear optical properties are analysed in detail. Clay minerals often play a significant role in the occurrence of specific photophysical phenomena such as resonance energy transfer and luminescence quenching and may influence various reactions, such as conformational changes in dye molecules, photochromism, photoisomerization, photosensitization and other photochemical processes. Routes to synthesize various types of hybrid materials are also described here. The relevance of DCHS for clay research, chemistry and materials science is summarized briefly.

Initial exchange of Cu(II)-montmorillonite by tetrapropylammonium (TPA) or tetramethylammonium (TMA) ions results in segregation of different ions in randomly interstratified layers, with particular preference for TPA over Cu(II) during exchange. More complete exchange reverses this preference and both Cu(II)-TPA and Cu(II)-TMA clays become more homogeneous. The copper ions of the homogeneous Cu(II)-TPA clays are not fully hydrated while the TMA ions have less effect than TPA on the hydration of copper, probably a result of the smaller radius and higher hydration energy of TMA. Methods of X-ray diffraction, thermogravimetric analysis, BET surface area determinations, as well as infrared and electron spin resonance spectroscopy, are used in supplying evidence of cation distribution and hydration properties of these clays. Definite changes in the properties of hydrated copper when associated with tetraalkylammonium ions on the clay surface are indicated.

Dehydration and rehydration of a phlogopitic Ca-vermiculite were studied by thermoanalysis (TG, DSC) and by in situ X-ray powder diffractometry. A detailed analysis of the relationship between temperature and state of hydration of the vermiculite close to equilibrium at atmospheric pressure was rendered possible by use of low heating rates in combination with a fast recording position-sensitive detector. The results reveal the existence of a number of distinct states of hydration characterized by basal spacings of 1.515, 1.493, 1.473, 1.188, 1.176 and 0.95 nm. In confirmation of results obtained earlier with Mg-vermiculite, regular interstratification occurred at dehydration during the transition between two- to one- and between one- to zero-layer hydrates showing integral series of 00l reflections with basal spacings of 2.67 and 2.11 nm, respectively.

Ferric illite in the Neoproterozoic Penganga Group, southern India, occurs in a lenticular unit of reworked arkoses conformably enclosed in carbonate mudstones, deposited in a shelf-margin carbonate slope setting influenced by deep marine sediment gravity flows. The structures and textures of the arkoses suggest emplacement by fine-grained debris flows and deposition in channels incised into the carbonate slope.

Ferric illite is sparse in the arkoses and has small concentrations and grainsizes within the same size fraction of the associated detritus, uniform chemical composition and an association with reworked facies. It consists predominantly of granular grains that are mostly sorted spherical, ovoid, capsule-shaped and vermicular peloids; many broken and micaceous. These attributes provide a comprehensive framework for suggesting an allogenic origin for the ferric illite previously interpreted as authigenic. The methodology adopted here is a useful approach in the interpretation of in situ vs. reworked origins of glauconitic minerals.

Measurements of water desorption and sorption on four Ca-saturated illitic clays show that the shapes of the isotherms are very similar to those for other oxide surfaces, indicating that the formation of water multilayers is quantitatively similar. This enables graphs of multilayer thickness against mass sorbed to be drawn and used to assess microporosity. Hysteresis occurs and this is attributed to loss of external surface as drying brings platy particles in close face-to-face contact. Mixed-layer mica-smectites, however, exhibit no microporosity by this test and behave as if all surfaces are freely accessible to multilayer formation. The reason for this is not at present understood.

The Triassic-Jurassic boundary (TJB) is marked by one of the five largest Phanerozoic mass extinctions. To constrain existing models for TJB events, we obtained a stratigraphically highly resolved dataset from a marine section at Kendlbachgraben, Austria.

The topmost Triassic Kössen Formation contains low to medium-charged smectite and vermiculite as alteration products of mafic-ultramafic minerals. The clay minerals in the boundary mudstone are kaolinite ⩾ illite + muscovite ⨠ smectite > chlorite. Predominant kaolinite suggests humid climate and abundant terrigenous input. In the lowermost Jurassic, the clay mineral pattern changes to illite + muscovite ⨠ kaolinite ⨠ smectite, which reflects change to less humid and more moderate climate.

The topmost Kössen Formation also contains clay spherules. Their composition, shape and size indicate that they are alteration products of airborne volcanic glass droplets solidified in the air, settled in the sea and altered rapidly with negligible transport in terrestrial or marine environments. Our data are consistent with sudden climatic change at the TJB, as a result of large-scale volcanic activity of the Central Atlantic Magmatic Province which produced distal airfall volcanic ash.

Tertiary sediments are of restricted occurrence in the onshore British Isles but occur extensively offshore, attaining thicknesses of ~4 km in the Faroe—Shetland Basin and ~3 km in the North Sea Basin. Clay mineral stratigraphic studies of the North Sea Paleocene to Lower Miocene successions show a dominance of smectite (and smectite-rich illite-smectite) with minor illite, kaolin and chlorite. Abundant smectite in the Paleocene and Eocene reflects alteration of volcanic ash derived from pyroclastic activity associated with the opening of the North Atlantic between Greenland and Europe. However, the persistence of high smectite into the Oligocene and Middle Miocene indicates that smectite-rich soils on adjacent land areas may also have been an important source of detrital clays. An upwards change to illite-dominated assemblages in the Middle Miocene reflects higher rates of erosion and detrital clay supply, with a subsequent increase in chlorite reflecting climatic cooling. The persistence of smectite-rich assemblages to depths of >3000 m in the offshore indicates little burial-related diagenesis within the mudstone succession, possibly as a consequence of over-pressuring. Despite the importance of Paleocene and Eocene sandstones as hydrocarbon reservoirs in the North Sea and Faroe-Shetland basins, there are few published details of the authigenic clays. The principal clay cements in these sandstones are kaolin and chlorite, with only minor illite reported.

The offshore successions provide a valuable background to the interpretation of the more intensively studied, but stratigraphically less complete, onshore Tertiary successions. The most extensive onshore successions occur in the London and Hampshire basins where sediments of Paleocene to earliest Oligocene age are preserved. Here clay assemblages are dominated by illite and smectite with subordinate kaolin and chlorite. The relatively large smectite content of these successions is also attributed primarily to the alteration of volcanic ash. Associated non-smectitic clays are largely detrital in origin and sourced from areas to the west, with reworking of laterites and “china clay” deposits developed over Cornish granites. Authigenic clays include glauconite (sensu lato), early diagenetic kaolin that has replaced muscovite (principally in the London Clay Formation of the London Basin) and smectite that has replaced ash. Pedogenesis has extensively modified the assemblages in the Reading Formation and Solent Group. Tertiary sediments are largely missing from onshore northern and western Britain, but clays and sands of Eocene and Oligocene age are locally preserved in small fault-bounded basins. Here, clay assemblages are dominated by kaolin with minor illite.

Isomorphic substitution in goethites is common in nature and the properties of goethites generally change as a function of the degree of substitution (e.g. Al-goethites). In synthetic goethites, substitution by other elements such as Co is also known. Recent literature indicates that the influence of Al and Co on the unit-cell dimensions of goethite is similar. In contrast to Al-goethites, however, little is known about other properties of Co-goethites and in this study some properties of synthetic Co-goethites were investigated by XRD, IR, TEM, TGA and reductive dissolution techniques. Eight goethite samples (S1 to S8) with varying Co concentrations were synthesized from mixed alkaline solutions of Fe(III) nitrate and Co(II) nitrate, aged at 63°C and ambient pressure. The goethites contained up to 9.5 mol.% Co. Their redness increased with Co concentration, e.g. 0.5 Y 6.0/6.4 for S1 and 6.4 YR 3.3/3.2 for S8. Surface area ranged from 46 to 88 m2/g. Unit-cell parameters a, b, c and v all showed a negative linear dependency on the Co concentration of the goethites. Transmission and diffuse reflectance IR spectrometry showed the presence of strong bands which were interpreted as v-OH, δ-OH and γ-OH vibrations. The δ-OH and γ-OH band positions showed a positive linear dependency on the Co concentration of the samples. Dehydroxylation occurred between 280 and 315°C and dehydroxylation peak positions tended to decrease with increasing Co concentrations. As with Al-goethites, Co-goethite reductive dissolution rates decreased parabolically with increasing substitution. X-ray diffraction and IR analyses, TGA and congruent reductive dissolution suggest the existence of single phases, i.e. Co-goethites of varying degrees of isomorphic substitution.

The electron microscope has been used to study the mechanisms of thermal decomposition of kaolinite in the temperature range 800-1350°C. Three main reaction mechanisms appear to be important in this temperature range. At 850°C metakaolinite breaks down to produce an amorphous defect oxide phase which is homogeneous and finely porous. When heated at 900°C the reaction product is a defect spinel with strongly preferred orientation and microporous structure. This defect spinel phase is observed in the temperature range 900-1150°C and shows little change in microstructure throughout this temperature range where the secondary development of muUite also occurs to a limited extent. Above 1150°C mullite develops in quantity and appears to represent the bulk of the reaction product at 1200°C.

An attempt has been made to assess new potential applications for the Bailén clays, traditionally used for manufacturing bricks, based on mineralogical, chemical, particle size, plasticity and firing results. Raw materials and mixtures used by the local factory were selected and tested with the addition of some diatomite, feldspar or kaolin. Based on their properties, clay materials from Bailén might be suitable for making porous red wall tiles, clinker, vitrified red floor tiles and porous light-coloured wall tiles by pressing; the first could be manufactured from the raw materials and mixtures currently used by the local manufactures. On the other hand, stoneware shaped by extrusion, such as perforated bricks, facing bricks and roofing tiles, can be also manufactured from the mixtures used at the factory if they contain 20-25% carbonate and small amounts of iron oxides; lightweight bricks require black and yellow clays with diatomite.

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.

Raman spectra of a selection of kaolins with widely varying TiO2 contents revealed the presence of anatase in 17 of 18 samples. A significant positive correlation was observed between the intensity of the main anatase Raman band at ~145 cm-1 and the total TiO2 contents of the kaolins as determined by chemical analysis. No TiO2 modification other than anatase was detected in any of the samples.

The determination of the anatase contents in kaolins by XRD becomes increasingly difficult as the concentration of this mineral decreases below ~0.5%. In contrast, anatase and brookite concentrations an order of magnitude lower can still be readily identified by Raman spectroscopy. The specificity and sensitivity of Raman spectroscopy for these TiO2 polymorphs, coupled with the simplicity and rapidity of measurement, therefore make this a viable technique for the routine study of these accessory minerals in kaolins.

In the course of some studies on the effects of anions on the viscosities of clay suspensions, it was observed that anions such as pyro- and metaphosphate, oxalate and fluoride were much more effective in reducing the viscosity of kaolih suspensions than were chloride and nitrate. There is relatively little information available regarding the specific adsorption of anions by clay minerals; it is known, however, that soils take up considerable quantities of orthophosphate from acid solutions. Whether the active component of the soil, in this respect, is the clay mineral or hydrated iron and aluminium oxides, the adsorbed phosphate may be readily released by shaking the soil with neutral or acid solutions containing fluoride, oxalate, citrate or malonate. In addition, a soil which is normally capable of taking up appreciable quantities of phosphate will not do so if fluoride is present in the phosphate solution. It has been recognized that the ability of this group of anions to form soluble complexes with iron and aluminium is responsible for their effectiveness in this respect.

K-Ar dating of mixed-layer illite-smectite from clay fractions extracted from pyroclastic horizons was used to address the controversy about the age and mechanism of the thermal alteration of Carboniferous rocks from the Upper Silesia Coal Basin (USCB). The clay fractions were also investigated by X-ray diffraction in order to select for dating samples possibly rich in illitesmectite, and to evaluate the K-Ar dates for possible contamination by K-bearing pre-diagenetic minerals, of pyroclastic or epiclastic origin.

The K-Ar dates document intense Variscian tectonic burial illitization produced by thrusting (~290 Ma) in the SW of the basin, and the lack of intense burial illitization in the NE, which is consistent with sedimentological models of the basin. The burial illitization in its final phase (<30%S in illite-smectite) involved incorporation of measurable amounts of ammonium cation in the illite structure (substitution for K).

Advanced illitization in the NE of the basin is much younger than its tectonic inversion (uplift and erosion started in Permian), and the corresponding K-Ar dates have to be interpreted as the result of a Mesozoic thermal event, which produced widespread pervasive illitization at shallow depth. This event was dated at 175 Ma, but it may have started earlier and could have lasted longer. This conclusion is consistent with widespread evidence of a major Mesozoic thermal event all over Central Europe, produced by rifting and lithospheric thinning during the opening of the Tethys and Atlantic oceans.

This study demonstrates that smectite illitization histories may be very complex, and that the nature of the illitization mechanism results in mixed K-Ar dates encompassing pro-longed or multiple illitization histories. Dating of several grain-size fractions may help to unravel such histories.

When a calibration using data from Neogene sedimentary basins is applied, vitrinite reflectance and %S in I-S indicate similar palaeotemperatures of tectonic burial diagenesis in the USCB, but they produce very different estimates of the temperature of the thermal event.

Modem disc centrifuge technology has extended the range of application of sedimentation particle size analysis to include the submicron region. An overall size range of approximately 10 nm to 100 pm is now accessible. The principles of both the disc centrifuge photosedimentometer, which employs optical detection with full Mie light scattering corrections, and the X-ray disc centrifuge are described. Examples of their application to a variety of samples are given to illustrate the performance characteristics of the instruments including a direct comparison of resolving power with that of the laser diffraction technique.