A study was made of the extent to which the lateral surfaces contribute to the surface area of five kaolinites of different crystallinities. Methods used included the low-temperature adsorption of N2 and Ar as measured by a volumetric technique coupled with microcalorimetry, the interpretation of the adsorption isotherms of alkyldodecylammonium ions, particle-size distribution curves, and shadowed transmission electron microscopy. With the exception of surfactant adsorption and adsorption calorimetry using Ar, these methods gave different and debatable results. For instance, specific lateral surface area values expressed as a percentage of total specific surface area varied from 17·0 to 40·4% for the most crystalline sample and from 12·0 to 54·3% for the least crystalline. It is shown that the decrease in crystallinity of samples is accompanied by a reduction in crystallite size from 0·8 to 0·08 µm and a decrease in lateral surface area from 34·0 to 12·0%.

Low-dip fractures in the Lac du Bonnet granite pluton, SE Manitoba, contain abundant illite. Petrographic examination showed that the illite has three modes of occurrence: (i) alteration product of biotite, (ii) microfracture (< 1 mm width) filling, (iii) macrofracture (> 1 mm) filling. Microprobe analyses of these three types of illites in a single sample gave distinct compositional characteristics that defined an evolutionary trend, depicting Al2O3 enrichment, on an Al2O3−(K2O + Na2O)−(MgO + FeO) triangular diagram. White micas in the rock matrix adjacent to illite-bearing fractures have higher K and Al contents than all the three types of illites, implying that they formed under different conditions. The sorption of four radionuclides, 137Cs, 147Pm, 241Am and 90Sr, under oxic conditions on illite-bearing polished sections was also investigated, using autoradiography combined with petrographic examination. Illite showed greater sorption compared with other minerals present in the polished sections.

Nous présentons une méthode de calcul de l'énergie totale d'une structure cristallińe (énergie électrostatique, énergie de van der Waals, et énergie de répulsion). Nous utilisons ensuite cette méthode pour étudier une série de phyllosilicates (talc, pyrophyllite, muscovite et phlogopite), pour comparer et discuter leurs propriétés physico-chimiques en particulier l'énergi de liaison interfoliaire et la distance interlamellaire. Nous constatons que des méthodes de calcul, basées sur des expressions empiriques différentes de l'énergie de répulsion, conduisent à des résultats relatifs analogues. Nous vérifions que la distance interlamellaire calculée approche la distance mesurée à 0·1 Å près. Nous calculons des énergies de liaison interfoliaire du talc et de la pyrophyllite (de l'ordre de 30 Kcal/mol) plus faibles que celles de la muscovite et de la phlogopite (de l'ordre de 60 Kcal/mol).

Four major sedimentary sequences of the Triassic and Upper Jurassic of the Main Claymore Oilfield of the North Sea each contain a characteristic suite of diagenetic minerals and fabrics. (1) Triassic Skagerrak Formation fluvial sandstones contain early authigenic pore-lining smectite, together with kaolinite and chlorite which form grain replacements and pore fills. Quartz and feldspar overgrowths are minor. Ferroan dolomite forms a late diagenetic patchy poikilotopic cement. Smectite is converted to illite-smectite in a 5 m thick zone beneath the sub-Jurassic unconformity. Smectite formed early in diagenesis prior to oil migration and destroyed permeability. Thus oil is not found in these sandstones although they occur in the oilzone. (2) The Piper Formation (late Oxfordian/early Kimmeridgian) paralic deposits mainly contain authigenic, pore-lining illite-smectite, vermicular kaolinite grain replacements and pore fills. Quartz overgrowths are generally well developed. (3) The Kimmeridge Clay Formation (early Kimmeridgian/early Volgian) comprises thin marine sandstone turbidites, contained within a thick siltstone/shale sequence. In the sandstones (the ‘Ten Foot Sandstone’) discrete double-ended quartz crystals (1–20 µm) developed prior to quartz, K- and Na-feldspar overgrowths. Only minor kaolinite and lllite-smectite are present. Late diagenetic dolomitic occurs as a patchy poikilotopic cement and as clusters of pore-filling rhombs. (4) The Claymore Sandstone Member (early to middle Volgian) thick marine sandstone turbidites are interbedded with thin siltstones/shales. Sandstones have well-developed quartz, K and Na-feldspar overgrowths, and kaolinite and illite-smectite occur as grain replacements and rarely as pore fills. Late-diagenetic dolomite and ferroan dolomite form poikilotopic cement and clusters of pore-filling rhombs. The major factors which control diagenetic features are depositional environment and associated porewater together with original mineralogy. Burial history and textural features of the sandstones also have important influences. Reservoir quality is controlled by a complex interplay of these features.

Geotechnical properties and behaviour are described of the very wet, halloysitic, residual clay found in the dense rain forest at Monasavu, Viti Levu, Fiji, where the annual rainfall can exceed 5 m. The tropical climatic conditions have caused deep weathering of sandstones and produced a highly plastic clay with low density and a natural moisture content greatly in excess of the standard compaction optimum. This clay was found to contain halloysite which was ‘amorphous’ rather than crystalline. The material was used in this natural state in an 85-m high rockfill dam at Monasavu Falls as an unusually soft core, the construction of which involved unconventionally light compaction by low-ground-pressure-tracked dozers. Its resulting behaviour in terms of three-dimensional total and effective stresses, stress paths and deformations throughout the construction, impounding and full reservoir stages was closely monitored. This behaviour is examined in the light of the clay's classification, mineralogical, compaction and engineering properties determined before and during construction. Despite its unusual properties, it is concluded that the clay is a good engineering material, behaving like others containing halloysite in the more common tubular form, and, moreover, that the high natural moisture content is of positive benefit.

Different types of chlorite and related mixed-layer minerals have been found in profiles developed on ultrabasic rocks of Ivory Coast and Brazil. Normal chlorites, with low K and Ni contents, are of hydrothermal origin and are situated at the bottom of the alteration profile. At the top of the profile the mixed-layer minerals are Ni-chlorite/vermiculite, which formed under weathering conditions, or K-chlorite/vermiculite, resulting from the alteration of mica. The Ni-content of the chlorite/vermiculite can reach 10% NiO.

Dans ce travail on a étudié l'influence des conditions expérimentales du traitement acide d'une sépiolite sur la vitesse d'extraction des ions Mg et la variation des propriétés texturales des produits résultants. On a élaboré un modèle cinétique pour l'attaque acide de la sépiolite ce qui nous a permis de calculer les paramètres cinétiques et, en dernier lieu d'obtenir des valeurs pour l'energie d'activation du processus.

Calcite cementation and extensive dissolution of feldspar with formation of authigenic kaolinite, quartz cement and secondary porosity are the main diagenetic processes in the deeply buried Hild Field. Mineralogical and isotopic analyses, reservoir pressure and depositional environment suggest that these diagenetic processes occurred prior to burial at a depth of 1·5–2 km. The timing of the diagenetic sequence suggests that feldspar dissolution is related to meteoric water flow. Calcite occurs as an early diagenetic iron-poor cement, and as two types of later diagenetic (<120°C) ferroan calcite cements. The ferroan calcites are mainly an in situ dissolution-reprecipitation product of the early diagenetic phase. Extensive local dissolution of calcite was important for forming secondary porosity which is closely associated with a prominent ‘gas chimney’ in the area studied. A high CO2 content in the natural gases of the reservoir suggests that the solvent was carbonic acid formed from CO2 generated during thermal maturation of organic matter. Calcite dissolution probably occurred between 70° and 100°C.

IR spectra of antigorite and sepiolite show an absorption band at ∼ 1200 cm−1. Spectra of palygorskite show several small absorptions between 1140–1200 cm−1. Since these three minerals are the only layer-silicates which show this absorption this band was assigned to Si-O-Si groups which serve as bridges between alternating alumino-Mg-silicate ribbons. By comparing the location of this band to bands observed in the spectra of P=O groups it was concluded that the contribution of π bonding in the bridging Si-O-Si group is of a high order. Similar conclusions were drawn after comparing the spectra of antigorite, sepiolite and palygorskite with those of various pyrosilicates. An inversion of the tetrahedral sheet requires an Si-O-Si angle of 180° which can be stabilized by dπ-pπ bonding in the Si-O-Si group. Due to the inductive effect of the octahedral sheet this type of bonding may occur in trioctahedral clay silicates, but is not to be expected in dioctahedral clay silicates.

The chemiphoresis of montmorillonite saturated with Na, K, Li or Ca was studied in a system where corrosive dissolution of Al, Fe, Zn or Cu metal plates took place in the presence of HF and H2O2. The deposition of the clay as well as metal dissolution were found to be a function of indicating that the electrochemical reaction is controlled principally by diffusion of the reacting species to the metal-liquid interface. The deposition increased with clay concentration and was lower for Ca-clay than for Na-, K- or Li-clay. It is shown that chemiphoresis alone does not provide sufficient data for the calculation of particle mobility and that other types of measurement are necessary. A relationship between particle deposition and electrical conductivity was developed, and examined experimentally with satisfactory results.

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.

Selected-area electron diffraction has been used to examine ferrihydrite coatings on kaolinite crystals and is shown to provide a sensitive means of detection. It also gives better diffraction patterns of ferrihydrite than does XRD and the patterns sometimes give additional indications of the crystal size. It is suggested that the technique may be useful in examining other coatings on soils and clays.

A tightly cemented series of marine sandstones, interbedded with shales and mudstones, occurs in the lower part of the Kimmeridge Clay Formation (Kimmeridgian to Ryazanian) of Arco Well 14/26-1 (Core No. 5, 8067–8085 ft). The well is on the northern flank of the Fraserburgh Spur Basement Ridge. The sediments are in the immature stage of hydrocarbon generation and are now at their maximum temperature and burial depth: the bottom hole temperature is 75°C. The sandstone diagenesis was complex, essentially of an intrinsic type, and took place under considerable overpressures. Initially a series of early cements was precipitated (minor chalcedony, quartz, feldspar, ferroan calcite, non-ferroan dolomite and major ferroan dolomite). A later phase of diagenesis embraced two periods of intrastratal solution (each affecting both the silicate and the carbonate components of the sediment) separated by a phase of calcite precipitation and followed by a phase of kaolinite cementation. The early cements are interpreted as being of the intrinsic miagenetic type. The later phase of diagenesis (alternating intrastratal solution and cement precipitation) resulted from the interaction of (i) the biotic breakdown of organic matter by thermophyllic micro-organisms and (ii) the abiotic thermal alteration of organic matter with the mineral components of the sediment: of particular importance were varying PCO2 and the generation of carboxylic and phenolic acids. The diagenetic pattern is closely comparable to that known from various Upper Jurassic sandy shelf sediments in other parts of the northern North Sea which have very different burial histories.

Authigenic chlorites occurring as pore linings in reservoir sandstones have been investigated by XRD and TEM/EDAX. Both methods identified the Ib (β = 90°) polytype. TEM/EDAX analyses suggest that the chlorites are Al-rich, Mg-chamosites with Fe/(Fe + Mg) > 0·47. Octahedral Al exceeds tetrahedral Al, resulting in octahedral totals of less than the theoretical 12·0. Compositions were estimated from XRD data using the equations after Brindley (1961) and Shirozu (1958). XRD-determined compositions are relatively enriched in tetrahedral Al and octahedral Mg, giving Fe/(Fe + Mg) > 0·4 and suggesting that the chlorites are Al-rich clinochlores. XRD estimates plot in the same compositional area as authigenic Ib (β = 90°) chlorites of Hayes (1970), but also within the compositional area of metamorphic chlorites. Caution should be exercised when estimating the composition of sedimentary chlorites by XRD as results appear to overestimate Mg content because of the excess of octahedral R3+ over tetrahedral R3+.

The mechanism of Ni-Mg substitution has been studied by X-ray absorption spectroscopy in phyllosilicates belonging mainly to the lizardite-nepouite and kerolite-pimelite series. Two types of information were obtained: (1) Analysis of nickel K-edge spectra under high resolution confirmed that Ni atoms were substituted for Mg atoms. There was no evidence for 4-fold coordinated Ni. (2) Extended X-ray absorption fine structure (EXAFS) was sensitive to atomic pair-correlations and gave access to the radial distribution function around Ni atoms. For all samples, this function gave two peaks. The first one was related to the (O,OH) coordination shell and analysis confirmed that Ni atoms were 6-fold coordinated. The amplitude of the second peak was very sensitive to the atomic composition of the Ni-Mg second shell. It is shown that the intracrystalline distribution of Ni is never random within the octahedral sheet; Ni atoms are segregated into domains, the minimum size of which has been calculated. In the kerolite-pimelite series the mean domain size is at least 30 Å and EXAFS could not exclude the existence of pure Ni sheets. X-ray dispersive spectroscopy combined with TEM suggested that the minerals in this series have pure Ni layers associated with pure Mg layers. In the lizardite-nepouite series, Ni atoms are segregated into specific Ni-enriched areas, the exent of which depends on the specific chemical constitution of the sample. Distribution patterns are discussed with respect to the formation mechanisms of these ore minerals.

The diagenetic history of the Upper Jurassic Fulmar Formation of the Central North Sea is described with emphasis on the Fulmar Field. The Fulmar Formation was deposited on a variably subsiding shallow-marine shelf under the influence of halokinetic and fault movements. The sediments are extensively bio-destratified although large-scale cross-bedding is locally preserved. The dominant mechanism of deposition is thought to have been storm-generated currents. Soft-sediment deformation structures are common and are attributed to syn- and post-depositional dewatering of the sandstones. The dewatering was associated with fractures and shear zones which reflect tectonic instability resulting from periodic salt withdrawal and/or graben fault movements. The dewatering may have been initiated by repacking of the sediments during earth movements or by the gradual build-up and sudden release of overpressures due to compaction and/or clay mineral dehydration during rapid burial at the end of the Cretaceous. The formation is composed of arkosic sandstone of similar composition to Triassic sandstones from which it was probably derived. The sandstones also contain limited amounts of marine biogenic debris including sponge solenasters, bivalve shells, rare ammonites and belemnites. Initial diagenesis began with an environment-related phase during which quartz and feldspar overgrowths and chalcedony and calcite cements were precipitated. These cements appear to form concretions adjacent to local concentrations of sponge debris and shell debris, respectively, and were disturbed after their formation by fracturing and dewatering. This was followed by an early burial stage of diagenesis which resulted in extensive dolomite cementation and minor clay mineral authigenesis (illite and chlorite). The last phase of mineral growth was probably pyrite. During early burial diagenesis, secondary porosity after feldspar and/or carbonate was produced, although the exact timing is not clear. The lack of both stylolitic developments and extensive illitization indicates that the late burial diagenesis stage was never reached, although sufficient clay diagenesis occurred to destroy all traces of mixed-layer illite-smectite (present in some shallower wells). The main control on reservoir behaviour is primary depositional fabric. Diagenesis only overprints these controls. Locally-cemented fracture sets act as baffles to fluid flow, but they are not extensive and the reservoir acts as one unit.

On treatment with dodecylammonium chloride, a synthetic Na-saturated phyllomanganate undergoes a cation-exchange reaction in which the structure expands from a collapsed basal spacing of 7 Å or a hydrated one of 10 Å to ∼ 25·5 Å. The exchange reaction is strongly influenced by the saturating cation in the original manganate and by the degree of hydration of the interlayer zone in which the exchangeable cations are located. Of the 12 cations tested, from Groups IA, IIA and IIB of the Periodic Table, only Co-manganate undergoes alkylammonium exchange when fully-dehydrated by evacuation. The results are discussed in the context of existing knowledge of the synthetic phyllomanganate and, by extrapolation, the potential value of the technique in the characterization of natural manganates has been assessed.

The pore-size distribution of kaolinite has been studied by nitrogen desorption isotherms. A new method is proposed which takes account of the fact that the intraparticle or ‘internal’ area is small in comparison with the total surface area. The crystals form dihedral angles with one another, and the irregularities of the crystal edges form a slit-shaped internal pore system. When the nitrogen pressure increases, the condensed volume in the pores grows by an amount greater than predicted by de Boer's law. This excess is shown to result from capillary condensation in bevelled pores and this accounts for the main part of the intercrystalline or ‘external’ porosity. A model of condensation in bevelled capillaries has been developed and its range of validity determined.

Boehmite and lepidocrocite, in the form of thin plates with well-developed (010) faces parallel to the constituent layers, show one predominant absorption band due to OH stretching of two-coordinated surface hydroxyl groups, which are shown to be unreactive towards phosphate. In very fine grained preparations of lepidocrocite, two other species of surface hydroxyl are detected, presumably associated with (100) and (001) faces. Marked differences in the frequencies of bulk vibrations between platy and rod-shaped lepidocrocite preparations can be explained partly by their crystal morphology, and partly by degree of crystalline order.

A detailed study of the IR spectrum of goethite is given with the aim of relating variations to crystalline order and particle size. The OH stretching vibrations are split into two active components at high frequency, plus two inactive ones at low frequency. Two different bending modes exist from site group splitting. Their active modes from factor group splitting are at lower frequencies than the uncoupled ones. The lattice bands at 630 and 400 cm−1 correspond to Fe-O or Fe-OH stretching, approximately parallel to a and c, and thus respectively sensitive and not sensitive to the particle shape, as long as it remains elongated along c.