The clay mineralogy of the Cretaceous strata of the British Isles is described and discussed within its lithostratigraphical and biostratigraphical framework using published and unpublished sources as well as 1400 new clay mineral analyses. The regional clay mineral variation is described systematically for the following strata:

1. (1) Southern England — Purbeck Limestone Group (Berriasian/Ryazanian; Lulworth and Durlston formations), Wealden Group (Valanginian—Barremian/Aptian; Ashdown, Wadhurst Clay, Tunbridge Wells Sands, Grinstead Clay Member, Wealden Clay, Wessex and Vectis formations), Lower Greensand (Aptian—Lower Albian; Atherfield Clay, Hythe, Sandgate, Folkestone Sands, Ferruginous Sands, Woburn Sands and Faringdon Sponge Gravels formations), Selborne Group (Middle—Upper Albian; Gault Clay and Upper Greensand formations) and the Chalk Group (Cenomanian—Lower Maastrichtian).

2. (2) Eastern England — Cromer Knoll Group (Ryazanian—Upper Albian; Speeton Clay, Spilsby Sandstone, Sandringham Sands, Claxby Ironstone, Tealby, Roach Ironstone, Dersingham, Carstone and Red Chalk (or Hunstanton Red Limestone) formations).

3. (3) Scotland — Inner Hebrides Group (Cenomanian—Campanian; Morvern Greensand, Gribun Chalk, Coire Riabhach Phosphatic Hibernian Greensands formations).

4. (4) Northern Ireland — Hibernian Greensands (Cenomanian—Santonian) and Ulster White Limestone formations (Santonian—Lower Maastrichtian).

The stratigraphical patterns of clay mineral variation divide naturally into two types; firstly, the more complex pattern of the Lower Cretaceous strata and secondly, the simple pattern of the Upper Cretaceous. Clay mineral variations in the non-marine and marine Lower Cretaceous strata of England are best explained by the interplay of two main clay mineral assemblages between which all gradations occur. The assemblage which dominates the main clay formations consists of mica, kaolin and poorly defined mixed-layer smectite-mica-vermiculite minerals, and sometimes includes vermiculite and traces of chlorite. It is dominantly of detrital origin and detailed evidence indicates it is derived largely from the reworking of Mesozoic sediments although ultimately from weathered Palaeozoic sediments and metasediments. Although mainly of detrital origin, this assemblage contains a persistent component that formed coevally with the approximate depositional age of its host sediment. Whether this component is of soil origin or was neoformed in the sediment shortly after deposition is unclear. There is little firm evidence indicating the sources of this clay mineral detritus. However, in the strata of the Wealden Group of southern England, mineral trends suggest three sources; one of these was to the west (Cornubian Massif), another must have been the Anglo- Brabant landmass. In the Selborne Group (Middle—Upper Albian) and in the overlying Lower Chalk (Cenomanian) where this assemblage makes its last appearance in the Cretaceous of England, there is good evidence of easterly and south-easterly sources.

The second main assemblage tends to be largely monominerallic, and usually dominated by smectite with or without small amounts of mica; less frequently, kaolin, berthierine or glauconite sensu lato is the sole or dominant component. It is considered to be of volcanogenic origin, derived from the argillization of volcanic ash under different conditions of deposition and diagenesis. The source of the ash in Berriasian—Aptian times seems to have been an extensive volcanic field in the southern part of the North Sea and in the Netherlands, whereas in the Albian (and extending into the Cenomanian) a westerly source dominated. The current controversy about the role of climate or pattern of volcanic activity controlling the clay mineral stratigraphy of the Lower Cretaceous is reviewed.

In the lower part of the Upper Cretaceous strata of England, Scotland and Ireland, sand-grade glauconite is particularly abundant. Much of it represents the glauconitization of pene- contemporanous volcanic ash, possibly of basaltic origin, associated with continental breakup and the opening up of the Atlantic Ocean and the earliest stages in the development of the Hebridean Tertiary Igneous Province. The Upper Cretaceous Chalk facies of England and Ireland is dominated by a smectite-rich clay assemblage containing mica, and the various hypotheses for its origin (detrital, neoformation, volcanogenic) are reviewed in the light of available mineralogical, chemical and geological data.

The clay fraction from the B horizon of a Psammentic Hapludalf containing vermiculite and smectite was treated with n-alkylammonium chloride ranging from nc = 6 to nc = 16. X-ray data were obtained by step-scanning, stored in a computer, corrected with the Lorentz and polarization factors and then fitted with a deconvolution programme. The layer charge was determined from the uncorrected, the corrected and the fitted diagrams, respectively. The evaluated confidence limits of ξ decreased in the same order revealing the vermiculite to be a high-charge type. The computed charge distribution of the smectite changed from an unlikely bimodal to a nearly symmetrical distribution.

Claystones of Kimmeridgian-Volgian-Ryazanian age are the main source rock for oil in the Central Trough, North Sea. During oil generation, illite layers form in illite-smectite (I-S) and the illitesmectites become short-range (IS) ordered and eventually long-range (ISII) ordered. The formation of illite layers involves dehydration and fixation of interlayer cations, K+ and NH4+. The content of soluble NH4 and K in core samples and the content of NH4 and K in I-S were determined, the NH4 by an isotope dilution method. In the Central Trough, soluble K+ decreases with depth, whereas soluble NH4+ increases with depth. From ∼3 km, the ratio NH4/K increases with depth, to an average of ∼0.5 at 4.4 km. In I-S, the ratio NH4/K shows a similar increase with depth. The NH4/K ratio increases significantly in I-S during ordering. It is concluded that NH4 fixation in I-S may be of general importance during burial diagenesis of oil source rocks.

A series of smectites was investigated to reveal the thickness distribution of crystallites. The Fourier decomposition technique of Bertaut-Warren-Averbach (MudMaster program) was applied to XRD reflections of <0.2 μm, glycolated Na-clays. It was shown that the thickness distribution is lognormal and the mean thickness ranges from 5.7 to 12.3 nm (3.4 – 7.3 layers). At higher humidities, characteristic of TEM sample preparation, the mean thicknesses decrease, but the differences in mean thickness between samples are preserved. Beidellites have the thickest crystallites. The relationships between the mean thickness, volume-weighted mean thickness and the parameters of the lognormal distribution were established. Calculation of these parameters is possible, using the area and the maximum intensity of the 001 reflection. The influence of the fluctuations of d-spacing on the peak width was shown. Smectite crystallites, dispersed into individual layers during infinite osmotic swelling and rebuilt through coagulation, recover their original mean thickness and thickness distribution.

Vermiculite and hydrobiotite both occur as alteration products of biotite pyroxenite near Libby, Montana. Hydrothermal and weathering studies and new chemical analyses by C. O. Ingamells suggest that the vermiculite is a product of leaching of biotite by ground waters; the hydrobiotite may be a higher temperature alteration product.

The alkali leaching of two aluminosilicates, kaolinite and metakaolinite, with aqueous NaOH has been studied. Both silicates gave hydroxysodalite (HS) with or without the evanescent zeolite NaA. X-ray diffraction and high-resolution 29Si and 27Al MAS-NMR spectroscopy provide information about the reaction sequence of the clay. The conversion starts with the formation of an amorphous gel precursor at a rate which depends on the alkali concentration but not on the choice of kaolinite or metakaolinite as starting material. The rate of zeolitization of this gel is much faster when it is obtained from kaolinite, probably because it is more homogeneous.

The thermal behaviour of a ferrous doped kaolin has been studied by Mössbauer spectroscopy and electron paramagnetic resonance spectroscopy. From the observations it is concluded that the iron substitutes trioctahedrally as Fe2+ in the ‘gibbsite-like’ sheet in place of dioctahedral aluminium. The g = 2 EPR signal is shown to be associated with these ferrous ‘cells’ which appear to occur in clusters. It is suggested that these ferrous cells are trapped within the normal dioctahedral aluminium structure. Dehydroxylation of the ferrous iron cells takes place between 623 and 673 K leading to the formation of an iron-rich pyroxene and, by 723 K, a ferric oxide. At temperatures > 723 K the pyroxene itself oxidizes to a second ferric oxide. The EPR signal changes at 623 K and disappears at 723 K. The signal is attributed to a trapped hole induced by X-irradiation, located near a silicon atom on the boundary between normal dioctahedral cells and trioctahedral Fe2+ cells. It is possible to extend the model to explain some puzzling features concerning the g = 2 EPR signals reported by other authors and to propose other effects which might result from the presence of these cells.

L'évolution structurale et texturale ainsi que le comportement hydrique de deux montmorillonites-Ca (Wyoming et grecque) ont été éudiés par microscopic électronique à transmission (MET) et plus précisément par analyse de la diffusion aux petits angles des rayons X (DPAX). L'étude au MET a permis de montrer qu'à faible contrainte, le matériau est formé par un réseau de particules déformables délimitant des pores de grandes dimensions (~2 μm). L'étude en DPAX des mêmes systèmes soumis à une contrainte de type succion a montré que: 1. Lors de la première dessiceation il y a d'abord déformation du réseau sans regroupement des particules (p ⩽ 1 bar), puis regroupement des particules face-face pour former des particules de plus grande épalsseur (p > 1 bar). On montre aussi que l'eau est essentiellement extraite de la porosité interparticulaire. 2. Lors de la réhydratation, on met en évidence qu'après dessiccation le système perd une grande partie de son aptitude à, reprendre de l'eau et que cette perte est d'autant plus importante que le niveau de dessiccation préalable a été élevé. Ceci est dû au falt qu'une partie de la porosité est réduite fi des espaces ayant la propriété de l'espace interfoliaire.

The thermal history of the Buntsandstein (Lower Triassic) sedimentary rocks that crop out in the Vosges Mountains, or are deeply buried in the Rhine Graben, was evaluated on the basis of a combined mineralogical, morphological, oxygen isotope and K-Ar-dating study of illite separates from five locations over a limited 120 km2 area. The results indicate a complex pre-rift evolution characterized by the following features: (1) in the northern Vosges, no record of diagenetic illite formation could be detected; (2) in the nearby Saverne rifting fracture-field, tectonic activity favoured the formation of faults in the crystalline basement ~210 Ma ago. This induced fluid migrations into the porous sandstone cover with illite precipitation occurring either repetitively over a period of ~25 Ma or as two separate events, the latter at ~185 Ma, affecting rocks to the east in the deeper part of the post-Eocene Upper Rhine Graben system; this latter stage of tectonic activity and fluid migration continued until 160 Ma, unless overprinted by another tectonic pulse at that time; (3) afterwards, the main tectonic activity moved to the Soultz-sous-Forêts area where two episodes could be identified at ~95 and 70 Ma by dating mineral crystallization; the latter illite age was also detected in more deeply buried Buntsandstein lithologies of the rift basin, west of Strasbourg, reflecting diverse crystallization under different physical and/or chemical conditions; (4) further illitization which at present is poorly constrained may have restarted ~55 My ago in the same deep part of the rift graben.

The youngest detected illitization age is clearly older than the main Miocene rifting episode of the Rhine Graben, suggesting that no illite crystallization occurred in the Buntsandstein sandstones during this tectonic event. This is explained by the fact that these rocks, as well as most of the underlying crystalline basement, were already sealed by fluid migration and mineralization during late Mesozoic rifting, and were therefore almost impermeable to the circulation of Tertiary fluids. The overall evolution of the region between the Vosges Mountains and the central Rhine Graben appears to be more complex than that of equivalent rock lithologies elsewhere in Western Europe. Several episodes identified here have been detected in other regions, but no single location exists which was affected by all events.

The distribution, profile morphology and mineralogy of deeply weathered gabbroic rocks in the basic igneous masses of Insch and Bogancloch, Aberdeenshire, have been studied. The saprolite is characterized by granular disintegration and spheroidal weathering with a relatively low degree of secondary mineral development. The upper part of the profile often shows evidence of mass movement and incorporation into overlying drift but below this zone the degree of alteration is generally uniform with depth. Feldspar and hornblende are largely unaffected, except by disintegration, but pyroxenes show varying degrees of weathering from the incipient development of amorphous iron oxides to replacement by reticulate networks or complete pseudomorphs of trioctahedral vermiculite. Biotite weathers to hydrobiotite and vermiculite, giving rise also, under certain conditions, to kaolinite-gibbsite vermiforms. The correspondence between occurrences of deep weathering and coarser textured biotite-bearing rocks can be related to the instability of this mineral. Consideration of the mineralogical changes found and the morphology of the profile of weathering suggest their formation under a warm, humid climatic regime, probably during the mid Tertiary times.

Amorphous hydroxides of Al, Fe, Mn, Mg, Zn, Co, Ni, etc., are capable of coprecipitating SiO2 even from very dilute (weathering) solutions. Silica minerals form only in those precipitates from solutions undersaturated with respect to amorphous silica (100 ppm SiO2 at 20°C). With higher SiO2 concentrations the precipitates remain amorphous. The size of the cations should allow 6-fold coordination and giving a brucite-like layer. Most suitably sized octahedral ions are Mg, Zn, Ni, Co and Fe2+ (size 0·78–0·82 Å), and chemically pure three- and two-layer clay minerals with these ions are easily synthesized. With a relatively high content of silica in solution (60 ppm SiO2 with 1–2·5 ppm metal) several smectite minerals could be synthesized. With a low content of silica in solution (5–20 ppm SiO2 and ca. 2 ppm metal) the serpentine minerals, could be synthesized.

It is possible to crystallize the difficult to form Al-clay minerals in a solid solution with these more easily synthesized clay minerals.

Clay minerals with the heavy metal ions of Ni, Co, Zn, and with Cu, Cr, etc., can be found in the weathering zone of Gossan and in the lateritic weathering crust of ultrabasic rocks.

We have determined the adsorption of RNA components (adenine, cytosine, uracil, ribose and phosphate) by Mg2+-exchanged montmorillonite. The isotherms for adenine, cytosine and uracil were of the C-type, the amount adsorbed increasing linearly with the equilibrium solute concentration. All three nucleic acid bases were apparently adsorbed by coordination to Mg2+ ions through a water bridge. Very little ribose was adsorbed by Mg-exchanged montmorillonite. The isotherm for phosphate was of the L-type. The plateau value of about 0.012 mmol g–1 indicated that phosphate adsorbed on the edge surface of montmorillonite. At comparable solute concentrations, adsorption decreased in the order adenine > cytosine > uracil. This observation reflects differences in basicity, size, and aqueous solubility among the three compounds.

The laser Raman microprobe spectrum of gibbsite displays four intense v (OH)- stretching bands at ~3365, 3435, 3525 and 3618 cm-1, bayerite shows three near 3425, 3545 and 3564 cm-1, nordstrandite has three near 3492, 3566 and 3623 cm-1, and doyleite one broad band centred at -3545 cm-1 with sometimes a prominent shoulder near 3615 cm-1. The four polymorphs also possess distinctly different Raman signatures of medium to strong bands in the region 100–1200 cm-1. These differences provide a non-destructive routine determinative procedure by direct microsampling of untreated crystals, fragments, and microcrystalline powders. Sample preparation is minimal. Excessive noise and non-quenchable fluorescence are the principle limitations of the technique.

Bentonite, which is envisaged as a promising engineered barrier material for the safe disposal of highly radioactive waste, was and is investigated in different large scale tests. The main focus was and is on the stability (or durability) of the bentonite. However, most countries concentrated on one or a few different bentonites only, regardless of the fact that bentonite performance in different applications is highly variable. Therefore, SKB (Svensk Kärnbränslehantering) set up the first large scale test which aimed at a direct comparison of different bentonites. This test was termed the ‘alternative buffer material test’ and considers eleven different clays which were either compacted (blocks) or put into cages to keep the material together. One so-called package consisted of thirty different blocks placed on top of each other. These blocks surrounded a heated iron tube 10 cm in diameter. Altogether three packages were installed in the underground test laboratory Äspö, Sweden. The first package was terminated 28 months after installation and the bentonite had been exposed for the maximum temperature (130°C) for about one year.

Almost all geochemical and mineralogical alterations of the different bentonites (apart from exchangeable cations) were restricted to the contact between iron and bentonite. The increase of the Fe2O3 content was attributed to corrosion of the tube. However, the typical 7 or 14 Å smectite alteration product was not found. At the contact of one sample, siderite was precipitated. Some samples showed anhydrite and organic carbon accumulation and some showed dissolution of clinoptilolite and cristobalite. IR spectroscopy, XRD, and XRF data indicated the formation of trioctahedral minerals/domains in the case of some bentonites. Even more data has to be collected before unambiguous conclusions concerning both alteration mechanisms and bentonite differences can be drawn.

The grain size of raw materials influences their behaviour during the technological process and affects many properties of building clay products. Over the last few years, brickworks have been technologically updated and grain size requirements have been modified to ensure good behaviour during shaping and drying. Therefore, the reference schemes used to assess the suitability of clays, such as the classic Winkler diagram, should be updated.

For this purpose, the grain-size distribution of 350 clays currently used in ~240 Italian plants was determined by X-ray monitoring of gravity sedimentation. Raw materials are basically represented by silty clays and clayey silts, while bodies present a narrower grain-size range. With reference to the Winkler diagram, most of the Italian bodies fall within the field of ‘thin-walled hollow bricks’, with no significant differentiation among the various product types.

In order to improve the grain-size characterization of bodies, a new classification scheme for Italian raw materials is proposed, based on three ranges: >10 µm, 2-10 µm and <2 µm, respectively. It allows distinction of specific grain-size features of bodies for (a) facing bricks; (b) roofing tiles; and (c) lightweight blocks, paving bricks and hollow slabs.

Piper and Tartan Fields are Upper Jurassic reservoirs located in fault blocks on either side of the Witch Ground Graben. The reservoirs are divided into a series of structural units, each successively downthrown towards the graben, covering a total depth interval of 8500–15 000 ft. Mudrocks interbedded with and overlying the reservoir sequence show a progressive increase in illite content with depth from ordered I/S clays with around 40% smectite to almost pure illites with low expandibility. K-Ar analyses on 13 <0·5 µm illite separates from mudrocks covering this depth interval give ages that range from 153 to 68 Ma. Shallowest samples give the oldest ages which are considered to reflect clay neoformation in Jurassic weathering profiles. In the 40Ar/K Harper diagram this data set falls on a mixing line which reflects the amount of smectite present. Deepest samples give the youngest ages and show a major reduction of 40Ar* with increasing K content indicating formation of new illite. These data are considered to document that ‘illitization’ proceeds via a two-step reaction: initial destruction of smectite followed by neoformation of illite. According to decompacted burial curves, ‘illitization’ took place 60–50 Ma ago. Reservoir sandstones have undergone a complex diagenetic history, involving multiple illite authigenesis. K-Ar analyses of 21 <0·5 µm illite separates selected across the oil-water contact in each of the main structural units show progressively younger ages in the water zone and with increasing depth of burial. Oldest ages in the oil zone (144–120 Ma) reflect eogenetic illite authigenesis whilst progressively younger ages in the water zone result from successive mesogenetic illite generations. The youngest age of 29 Ma was obtained from an illite-rich zone at the present oil-water contact in the Tartan downthrown block. Assuming illite authigenesis in the Tartan downthrown block took place shortly after oil accumulation, ∼29–35 Ma can be considered as a maximum age for the present oil accumulation. A minimum age for oil accumulation is calculated as 22 Ma on the basis of contamination of the 29-Ma sample with up to 10% of 93-Ma authigenic illite.

Despite many reviews and original articles, the actual crystal structure of tubular halloysites remains unclear. Analysis of the structural features of defect-free kaolinite, refined by Bish & von Dreele (1989), shows that the ordered 1Tc kaolinite structure can be described equally well by the orthogonal layer cell {a0, b0, γ0} (γ0 = 90°) or by two enantiomorphic oblique layer cells {a1, b1, γ1} and {a2, b2, γ2}, related to each other by a mirror plane. To simulate diffraction effects for tubular halloysite, the parameters and atomic coordinates of the orthogonal layer unit cell and the layer-displacement vectors t1 and t2 responsible for formation of the kaolinite enantiomorphs were deduced by transformation of the parameters of the defect-free kaolinite refined by Bish & von Dreele (1989). Modelling X-ray diffraction patterns show that the samples consist of either single, two or three phases, with the number and their structural features depending on the morphology of the particles. Samples formed of prismatic particles consist of halloysite-like structure (HLS), kaolinite-like structure (KLS) and halloysite cylindrical structure (HCS) phases occurring in various proportions. Samples of proper cylindrical tubes consist of a single HCS phase, whilst samples formed by particles having morphologies intermediate between proper cylindrical and well-developed prismatic forms consist of the KLS and HCS phases. The KLS phase is comparable to low-ordered platy kaolinite with identical unit-cell parameters, layer-displacement vectors and arbitrary stacking faults, except that the layer displacements are not random as in kaolinite, but are distributed at R = 1 such that t1 and t2 displacements have a strong tendency to be segregated. Structural parameters describing the HLS and KLS phases are identical, but in the HLS phase there is a strong tendency to the regular alternation of the t1 and t2 displacements, and the HLS phases do not contain arbitrary stacking faults. A characteristic feature of the three-phase prismatic samples is that the stacking of the layers along the c* axis is periodic and the layer thicknesses are similar to those of platy kaolinite. In contrast, in the KLS phase formed in samples with particles of intermediate morphologies, the hydrated 10 and 7.25 Å layers are interstratified. The relationship between the structural and morphological features of the coexisting phases suggests a sequence of phase formation from the centre to the surface of halloysite tubes that progresses from the HCS to the HLS via the KLS phase. The results of this study demonstrate that all kaolinite and halloysite (7 Å) varieties are built by the same fundamental structural units.

In soils and other weathering environments, hematite and goethite are usually formed in the presence of clay minerals. Two-line ferrihydrite was aged in the presence of six different clay minerals in aqueous suspension at 25°C and pH 4, 5, 6 and 7 for 16 years. The transformation into hematite/goethite mixtures was complete in the systems with gibbsite, kaolinite, illite and smectite, but incomplete in those with soil smectite and allophane. Soil smectite and allophane, as well as increasing pH, favoured hematite over goethite. The grainy and multi-domainic hematite crystals in the allophane system contained Si and Al (EDX) and showed a Si – O vibration at ∼920 cm– 1 (FTIR). The unit-cell contraction due to structural Al was counteracted by structural OH, which was removed at 200°C. Heating also increased the magnetic hyperfine field at RT by 1.2 – 1.6 T. Hematite crystals with irregular shape and grainy interior have also been observed in soils.

Sandstones and mudstones of the Skagerrak Formation from the Danish Sub-basin have been studied to assess the origin of the clay minerals, their diagenesis and their transformation/ conversion temperatures (compared to modelled maximum burial temperatures). Detrital smectite and vermiculite occur only at shallow levels. Conversion of smectite into random S-I took place at >47°C and of random S-I into ordered I-S at >74°C. The omnipresent illite increases in amount with burial. The amount of authigenic kaolinite (kaolin) decreases with increasing temperature (>75°C), possibly due to the growth of chlorite. Random S-C is converted into ordered S-C between 70°C and 105°C and chlorite is most abundant at maximum burial temperatures (150°C). This investigation suggests that diagenesis of clay minerals begins at relatively low temperatures, and emphasizes the importance of the availability of necessary ions (K+, Mg2+, Fe2+) for the reactions, besides time and temperature, as controlling parameters.

Factors influencing the degree of intercalation (‘reactivity’) of kaolinite group minerals have been investigated using six kaolin minerals, with variable crystallinity and particle size. Tests were performed to measure the degree of intercalation with potassium acetate, formamide, dimethylsulphoxide and hydrazine.

These experiments indicate that intercalation degree depends on a number of factors, including particle size, degree of ordering, type of guest molecules, method of intercalation, and presence and types of impurities. Anew method for determination of the degree of intercalation is proposed, which is not dependent on the intensity of complex reflections. The results indicate that formamide is the most sensitive reagent to distinguish differently ordered kaolin minerals whereas hydrazine appears as the most appropriate reagent to differentiate kaolin minerals from other 7 Å phases.