The REE contents in the clay-sized fractions of nineteen Cretaceous and Pliocene continental sediments, Portugal, were found to be correlated with kaolinite. No correlation is apparent between clay mineralogy and La/Lu or Eu/Sm ratios. The Eu anomaly is generally smaller (or even absent) in the clay-sized fraction than in the corresponding whole sediment, probably due to a greater ability of the clay minerals to accommodate Eu (as Eu2+) rather than the other REE released during weathering.

Bayerite forms a cascading, travertine-like deposit over volcanic tuffs on Raoul Island in the South Pacific where it is produced from episodic discharge of spent, caustic aluminate solutions from a hydrogen generator. Textural evidence indicates microbial activity has possibly been involved in formation of the hydroxide, as well as sodium carbonate aluminate, present in minor amounts. X-ray powder diffraction and infrared spectral studies failed to give confident identification of the bayerite, the identity being confirmed by laser Raman spectroscopy. A high quality spectrum was obtained extending from 3280 to 3680 cm−1 and from 100 to 1000 cm−1.

Devonian rocks from the Orcadian Basin show an extreme range of organic maturity. Mean vitrinite reflectance ranges from 0·6 to 10·5% and spore colour from yellow-orange to black. Illite/smectite (I/S) is abundant in the clay fraction of lacustrine mudrocks and shows variation in expandability from 30 to <5%. A correlation is observed between expandability and vitrinite reflectance, but the specific relationship is different in the Moray Firth and the Caithness-Orkney areas. Illite ‘crystallinity’ measurements in the Caithness-Orkney area are also correlated with vitrinite reflectance. Geological evidence favours an I/S origin from precursor smectite, and mineral and chemical analyses of lacustrine shales show no evidence for regional differences in composition that might affect illitization rates. The different relationships within each region are believed to result from the different relative response of organic maturity indicators and clay minerals to temperature and reaction time. The lower I/S expandabilities in the Caithness-Orkney region at a given vitrinite reflectance are attributed to relatively longer burial times.

Short-chain alkylammonium derivatives of montmorillonite (< 8 or 10 C atoms in the alkyl chain) adsorb alcohols in the micropores between the alkylammonium ions. The external surface area and the micropore volume are derived from comparison plots of ethanol and butanol adsorption isotherms. The micropore volume varies between ∼0 (decylammonium derivative) and 100µl/g (methylammonium derivative); the external surface area determined by ethanol and butanol gas adsorption is about 50 m2/g, and is almost independent of the alkyl chain length. In contact with the alcohols, the alkylammonium ions in the interlayer space remain in h1 or h2 arrangement (monolayers or bilayers of flat-lying alkylammonium ions); on the external surface they move into an upward position. The heat of immersion decreases strongly with increasing alkyl chain length to a minimum for decylammonium ions, the variation being very similar for ethanol, butanol, hexanol, octanol and decanol. Immersion in ethanol increases the external surface area at the expense of the internal surface area. In butanol and longer alcohols this area remains unchanged. The increase of the external surface is related mainly to changes in the less ordered regions around the core of the crystals which consists of coherent silicate layers. The heat of wetting is ∼ 110 mJ/m2 (external and internal surfaces). The integral enthalpy of adsorption of butanol, 40–50 kJ/mol, is independent of the alkyl chain length (nc ≤ 8).

Kaolins have been separated from sandstones from the Pugu Hills deposit, Tanzania, using a 15 mm glass hydrocyclone and a laboratory-scale multiple unit consisting of six 10 mm cyclones. Two types of sandstone were treated—containing a disordered kaolin (Pugu D) and a well-ordered variety (Pugu K)—to see whether products could be obtained that met particle-size specifications for paper manufacture. Pugu D gave a product that would meet specifications for both paper-filling and -coating applications with minimal processing, although the extremely fine-grained nature of this kaolin could lead to high viscosities in suspension. Processing of Pugu K gave products containing up to 97% kaolin and particle-size distributions that would meet specifications for filler and, possibly, coating clay. However, it was impossible to eliminate 3% or so of fine-grained quartz from these products and this could militate against use in paper manufacture.

Claystones of Kimmeridgian-Volgian(-Ryazanian) age are the main source rocks for oil in the Central Trough, North Sea, but they are too immature for oil generation in the Norwegian-Danish Basin. This paper describes the diagenesis of mixed-layer illite/smectite (I/S) in these source rocks as investigated by X-ray diffraction and high-resolution electron microscopy, interpretation for both methods being supported by computer simulations. Randomly-ordered I/S with ∼70% illite layers, together with discrete illite, kaolinite, and traces of chlorite and vermiculite, are detrital. The clay mineralogical data suggest the existence of an island at Gassum during part of the Upper Jurassic. Mixed-layer illite/smectite originating from volcanic ash is found in two wells in the Central Trough. The volcanism may be related to a period of stretching in the North Sea graben system during Jurassic-Lower Cretaceous time. Diagenesis has not altered the I/S in the Norwegian-Danish Basin. In the Central Trough, however, the amount of illite layers in I/S increases from ∼70% to ∼90% and the I/S becomes ordered. The volcanic clays have been changed to randomly ordered I/S with ∼50% illite layers. These changes occurred in the Central Trough simultaneously with oil generation.

Glutamic acid deamination was realized in the absence and in the presence of montmorillonite saturated with various metallic cations (Na+, Mn2+, Cu2+). The catalytic activity depends upon the interlayer exchangeable cation and the pH of the suspension. A maximum was observed near pH = 5–6. In the presence of the enzyme l-glutamate dehydrogenase and the coenzyme nicotinamide adenine dinucleotide, glutamic acid transforms into α-ketoglutaric acid, but in the presence of montmorillonite, it yields α-hydroxyglutaric acid and traces of butyric acid. However, kinetic and reaction yield are significantly reduced compared to the biological system.

Primary kaolins, related to Pliocene-Pleistocene volcanic rocks of acid to intermediate composition from the southern part of Kimolos island contain kaolinite and quartz ± cristobalite. Smectite is rarely present whereas alunite is common and more prevalent than baryte or gypsum. The kaolinites show structural disorder (Hinckley indices ranging from 0·6 to 1·1) and contain faults along the c*-axis. The elements Nb, Th, Ce and Sr, La, V constitute two groups with a strong intercorrelation and the kaolins are enriched in these elements compared to the parent rocks. K, Rb, Y and Ba are positively correlated with feldspar content and decrease with the intensity of kaolinization. The mineral assemblages suggest a zonal pattern which is thought to be related to different types of hydrothermal alteration. Starting from the triple point of the alunite-K-feldspar-K-mica-quartz association encountered in Kimolos, a tentative path is presented showing the approximate ranges in concentrations of K2SO4 and H2SO4 required for the formation of the various mineral assemblages.

Some of the many problems associated with the acquisition and interpretation of K-Ar isotope data for authigenic illites in porous sandstone lithologies are discussed. Difficulties arise from a lack of critical awareness of the assumptions made in deriving a K-Ar age of illite formation. Calculations are presented which imply that where sustained reservoir temperatures are high (> 150°C), erroneously low K-Ar ages could result from diffusive Ar loss. Very low levels of detrital contamination with other K-bearing minerals cause further difficulties. Even non-K-bearing contaminants may have a marked effect on apparent ages of illite ‘separates’. However, if considerable care is exercised during separation, the contamination problem is not intractable. The potential of the K-Ar technique to specify temporal development of the characteristics of reservoir rocks suggests that analytical refinements and basic experimental parameters are worth pursuit. Hypothetical examples of depth-age profiles are discussed in the context of their relevance to the timing and nature of hydrocarbon charging of reservoirs.

The chemical composition of the pyroaurite-type compound Fe(II)Fe(III) hydroxy-carbonate (‘green rust’) synthesised from freshly precipitated ferrihydrite and Fe(II) chloride solution at pH 7.0 (‘induced hydrolysis’) was determined. The compound was nearly stoichiometric, with the formula the Fe(II):Fe(III) ratio being independent of the Fe(II):Fe(III) ratio in the initial reaction mixture. It shows all the XRD peaks reported for this compound. Visible-near IR shows a broad peak at 650 nm which is ascribable to intervalence charge transfer and therefore the absorbance maximum decreases with increasing degree of oxidation. Wetting the material with compounds containing hydroxyl groups (such as glycerol or glucose) retards the oxidation of the otherwise very oxidation-sensitive compound. Similar polar organic compounds may stabilize the Fe(II)Fe(III) hydroxy-carbonate in wet soils. The importance of the green rust phase as an intermediate in the formation and transformation reactions of oxides and oxyhydroxides of iron in natural environments should not be ignored.

Five areally distinct mineral assemblages are recognized in the Inferior Oolite of S. England. In each area, vertical (stratigraphic) variations are insignificant. The five assemblages comprise varying proportions of illite, illite-smectite, kaolinite, chlorite and kaolinite-smectite, the mixed-layer clays being largely poorly crystalline and randomly interstratified. A predominantly detrital rather than authigenic origin is suggested for most of the clays. Shallow-water platform carbonates contain kaolinite with illite and illite-smectite. Kaolinite decreases in abundance away from former mid-Jurassic land areas, the deeper shelf and more basinal facies being dominated by illite and/or illite-smectite. Possible volcanic contributions to clay suites are suggested but cannot yet be fully evaluated. The palaeogeographic usefulness of clay mineral suites is confirmed, even in carbonate-dominated systems.

Room-temperature dehydration of aqueous coal slurries, coal extraction residue, or coal ash results in spontaneous luminescence. The phenomenon is characterized by a monotonic decay in photon activity which precedes a sharp rise in photon release. A maximum is reached within several minutes but subsequent decay is slower and photon emission continues for an extended period of time. The magnitude of photon activity is severely limited by the thickness of the strongly absorbing coal slurry. Prior removal of mineral matter from the coal appears to curtail the dehydration-induced phenomena, suggesting that clays or clay-organic interactions are responsible. Data also suggest that air is required as a medium for discharging the excited species.

Luminescence, induced by dehydration and by wetting with hydrazine and unsymmetrically substituted hydrazine, and related ESR spectra have been observed from several kaolinites, synthetically hydrated kaolinites, and metahalloysites. The amine-wetting luminescence results suggest that intercalation, not a chemiluminescence reaction, is the luminescence trigger. Correlation between dehydration-induced luminescence and g = 2 ESR signals associated with O−-centres in several natural halloysites, and concurrent diminution of the intensity of both these signal types as a function of aging in two 8.4 Å synthetically hydrated kaolinites, confirm a previously-reported relationship between the luminescence induced by dehydration and in the presence of O−-centres (holes, i.e., electron vacancies) in the tetrahedral sheet. Furthermore, the ESR spectra of the 8.4 Å hydrate showed a concurrent change in the line shape of the g = 4 signal from a shape usually associated with structural Fe in an ordered kaolinite, to a simpler one typically observed in more disordered kaolinite, halloysite, and montmorillonite. Either structural Fe centres and the O−-centres interact, or both are subject to factors previously associated with degree of order. The results question the long-term stability of the 8.4 Å hydrate, although XRD does not indicate interlayer collapse over this period. Complex inter-relationships are shown between intercalation, stored energy, structural Fe, and the degree of hydration which may be reflected in catalytic as well as spectroscopic properties of the clays.

Subarkosic arenites of the Middle Jurassic Garn Formation are important hydrocarbon reservoirs in the Haltenbanken area. XRD and petrographic analyses of core samples from 11 wells show that a transition from incipient to extensive illitization in these sandstones is associated with a present burial depth of 3·7 km below the sea floor, corresponding to a formation temperature of 140°C. Illite has formed by reaction between K-feldspar and earlier diagenetic kaolinite and probably also by alteration of mica. Although several of the cores are filled with hydrocarbons that probably were in place before base-Eocene (57 Ma), there are no indications that illitization was inhibited by the presence of hydrocarbons in pore spaces. It is therefore suggested that 20–30% residual water saturation is sufficient for extensive illitization to occur by short-range diffusive transport in a compositionally closed system. There is an unresolved problem regarding both the timing and cause of illitization. On the one hand, the extent of illitization in the 11 wells correlates with variations in both present formation temperature and thermal maturity, implying that the present burial depth of 3·7 km below the seafloor coincides with a critical thermal threshold for illitization. According to this interpretation, the times of illitization in the different wells should correlate with variations in burial history and should in several cases be as young as 3 Ma, when deposition of one kilometer of glacially-derived sediment sharply increased temperatures throughout the Haltenbanken area. On the other hand, conventional K-Ar analyses of illite separates give dates ranging from 31–55 Ma. In general, these dates appear to be too old to fit the interpretation that the degree of illitization is a simple function of present temperature or thermal maturity. This inconsistency may reflect errors in the K-Ar dates due to a contamination problem.

The diagenesis of Brent Group sandstones at Heather Field was studied to reconstruct time-dependent variations in reservoir quality, hydrodynamic history, and oil emplacement. Depositional facies, isotopic and trace-element composition of authigenic minerals, and present-day formation-water chemistry indicate several major changes in porewater chemistry related to both gravitational and compactional flow systems that significantly impacted diagenesis. Early cementation by calcite was related to influx of meteoric water and completely occludes porosity in certain areas of the Field, especially in lower reservoir zones. Geochemical, petrographic, and structural evidence indicate that average calcite precipitated at low to moderate temperature from reducing isotopically-depleted water having high levels of radiogenic Sr (40°–50°C, δ18O = −4 to −6‰, 87Sr/86Sr > 0·71). A major period of kaolinite precipitation and feldspar dissolution followed calcite cementation. The isotopic composition of pore-filling kaolinite shows Field-wide uniformity (δ18O average 13·8‰, δD average −53·2‰), suggesting thorough flushing of the reservoir by meteoric water and precipitation at low to moderate temperature (45°–60°C). Tectonic, burial, and thermal histories suggest that meteoric flushing occurred during the late-Cimmerian sea-level low, possibly in response to gravitational flow of meteoric water from exposed parts of the adjacent East Shetlands Platform. Illite and quartz diagenesis post-date kaolinite cementation, with illite K-Ar ages indicating precipitation through much of the Paleogene (55–27 Ma), coincident with migration of hydrocarbons from neighbouring sub-basins of the East Shetlands Basin. Illite stable isotopic data indicate precipitation in a system resulting from partial mixing of trapped meteoric pore-fluids with saline compaction water. The intensity of sandstone diagenesis is influenced by differences in the fluid migration history, content of detrital K-feldspar, and the time of hydrocarbon emplacement and results in spatial and temporal variations in reservoir quality.