The adsorption of various alkylammonium cations from aqueous solution by sodium and calcium montmorillonite has been studied. Adsorption occurred through an exchange reaction between the inorganic cations on the clay and the alkylammonium ions in solution. The affinity of the clay for these cations was linearly related to molecular weight, with the exception of the smaller methyl-ammonium and the larger quaternary ammonium ions. Comparison of primary, secondary and tertiary amines containing the same alkyl groups showed that the affinity of the clay was greatest for the primary amine and least for the tertiary. This behaviour has been interpreted in terms of the size and shape of the cations. X-ray diffraction analysis showed that no more than a single layer of adsorbed cations was present in the inter-lamellar space at maximum adsorption. Comparison between Δ-values and the thickness of the adsorbed ions showed that there was a contraction in the apparent contact distance of these cations. The amount of contraction could be accounted for by ‘keying’ of the adsorbed ions into the montmorillonite surface.

The complexes formed by ethylene glycol, HOCH2.CH2OH, and by glycerol, HOCH2.CHOH.CH2OH, with smectites (montmorillonite-saponite group), and vermiculites have received more attention than any other group of organo-silicate complexes. This interest arose in the first place from their use for identification purposes as proposed by MacEwan (1944, 1946) and by Bradley (1945b). Over the years, increasing attention has been given to the manner in which these complexes vary with the nature of the mineral, the magnitude and source of the charge on the silicate layers, and the number and kind of the exchangeable cations between the layers. The layer charge is determined most reliably from the full chemical analysis of a mineral, but more commonly is estimated from a measurement of cation exchange capacity.

Fundamental particles of illite-smectite from bentonites were separated into classes by high-speed centrifugation after infinite osmotic swelling of mixed-layer crystals, achieved by Na-exchange and dispersion in distilled water. In samples free of detrital contamination, the thinnest fundamental particles yield older K-Ar ages than the thicker fundamental particles. This implies that they do not preferentially lose radiogenic 40Ar due to size, and that the illitization process is a crystal growth mechanism (not nucleation plus growth). As a result, any K-Ar age of fundamental illite particles from bentonites is an integral over longer or shorter periods of time, depending on the thermal history of the rocks. In thick bentonite beds, the measured age difference between the beginning of the illitization process at the contact with the host rocks and the end in the centre of the bed records extremely slow K diffusion in these well compacted rocks. These data explain why measured K-Ar ages of illite-smectite from bentonites are younger than the corresponding age of shale illitization, inferred from the burial history of the basin. The finest technically separable size-fractions of associated shales (<0.02 μm) yield K-Ar dates* greater than the stratigraphic age. This observation points to incomplete recrystallization of detrital illite during burial diagenesis.

Infrared (IR) spectra of well-ordered kaolinites generally show four OH-stretching frequencies, near 3697, 3670, 3652 and 3620 cm-1. Raman spectra of the same kaolinites mostly show an additional band near 3686 cm-1, which, in the coarsely crystalline Keokuk kaolinite, largely replaces the 3695 cm-1 band. It is shown that the 3686 cm-1 band can be ascribed to a transverse optical crystal vibration involving the in-phase stretching vibration of the three inner-surface hydroxyl groups in the unit-cell. Raman exciting radiation, commonly of wavelength near 500 nm, can excite this crystal vibration in crystals of comparable and greater thickness.

Infrared studies are usually made on clay-size (<2 μm) particles, which have mean thicknesses of 30-150 nm. Infrared radiation of wavelength near 2.7 <m can only excite whole crystal vibrations perpendicular to the plates. The in-phase vibration of inner-surface OH groups in the whole-crystal mode lies at 3697 cm-1, which is the same frequency as that of the longitudinal optical mode in macroscopic crystals.

The conversion of smectite to illite has been studied in buried bentonites and shales of the East Slovak Neogene Basin, using X-ray diffraction analysis and transmission electron microscopy. A good correlation was observed in both rock types between the content of expandable layers in interstratified illite-smectite (I-S) minerals and burial depth (temperature), with shales from a given depth being markedly more illitic than bentonties. This difference disappeared at a depth of ~3 km, which represents a temperature of ~150°C The diameter of fundamental illite particles increased with decreasing expandability. Potassium fixation together with neoformation appear to be the mechanisms of conversion of smectite to illite.

Several new interlayer-grafted derivatives of kaolinite were synthesized by esterification of inner-surface hydroxyl groups with alkanols, diols and glycol mono-ethers starting with the dimethyl sulphoxide intercalate. The derivatives were characterized by X-ray powder diffractometry, thermal analysis, Fourier transform infrared spectroscopy and transmission electron microscopy. The grafted molecules are arranged in monolayers between the kaolinite layers, with typical basal spacings of ~11.3 Å. Rheological studies of aqueous dispersions of the modified kaolinites revealed an exponential increase of the yield value and apparent viscosity with increasing alkyl chain length of the grafted molecules.

Scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM) investigations of chlorite grain coatings from four different sandstone reservoirs indicate a progressive change in both texture and arrangement of chlorite particles from the contact with the detrital substratum to the centre of the pore. Such spatial distribution results from growth by geometrical selection. Geometrical selection of chlorite crystals proceeded during a single event of continuous growth which began before the consolidation of the sandy sediments, lasted through part of the subsequent mechanical compaction and ceased before the occurrence of quartz cement. Nanopetrographic investigations near the detrital quartz-chlorite coating interface demonstrate that inhibition of the quartz cement is due to the limitation of the epitaxial growth of quartz to the interparticular space at the base of the chlorite coating and not an absence of nucleation. It is suggested that these results can be applied to most of the sandstones which contain Fe-rich chlorite grain coatings.

Competitive adsorption of glyphosate and phosphate on goethite and gibbsite and on illite, montmorillonite and two kaolinites differing in surface area was evaluated. The results show that glyphosate and phosphate are competing for the adsorption sites, but the degree of competition depends on the adsorbent. On goethite the competition is very much in favour of phosphate, on gibbsite the competition is closer, but still phosphate is favoured, while on illite, montmorillonite and kaolinite the competition is almost equal. The amounts of glyphosate and phosphate, which can be adsorbed also depends on the adsorbent: the oxides adsorb more than the clay silicates. The amount adsorbed on kaolinite was dependent on the specific surface area. Changes in the surface area did not affect the competition between glyphosate and phosphate for adsorption sites. The results indicate that differences among soils of different mineralogical composition regarding the adsorption of glyphosate and phosphate can be expected.

The (02,11) X-ray diffraction band from a low-defect kaolinite from Cornwall (Hinckley index HI = 1·22) was examined to determine the defect structure. No combination of interlayer translations and admixing of dickite layers accurately modelled the observed diffraction pattern. Calculated diffraction patterns which gave a good agreement with the shape, position, and intensity of the observed peaks, uniformly had inter-peak intensities which were too weak. By treating the kaolinite as a mixture of low-defect (HI = 1·76) and moderate-defect (HI = 0·29) kaolinites, the agreement between the observed and calculated patterns was improved substantially. The existence of a mixture of two kaolinites was also found for a number of low-defect samples (HI > 0·4) from Georgia and Cornwall, and may be of even wider occurrence. The HI, which is very sensitive to the inner-peak intensities, does not estimate the types or abundances of various structural defects (the classical “crystallinity”), but is related directly, in a non-linear fashion, to the proportions of the two kinds of kaolinite which are present in the sample.

Complex formation between halloysites, from soil and geological sources, and a series of amides has been investigated. All the amides used can be intercalated to give single-layer complexes with basal spacings between 10·4 Å (for formamide) and 12·4 Å (for N,N-dimethylacetamide). When the interlayer space of halloysite has already been expanded by water, as is the case with fully hydrated samples, the rate and extent of intercalation depend more on the properties of the organic species than on the mineralogy of the clay. With partially and completely dehydrated halloysite, however, complex formation is influenced by the particle size, crystallinity, and iron content of the mineral. A large particle size, a high degree of crystallinity, and a low iron content are all conducive to complex formation. The iron content of halloysite also appears to affect particle shape. Low structural iron contents are associated with long tubular particles, intermediate contents with short and/or wide tubes, and high contents with spheroidal and other non-tubular forms. Halloysites containing high amounts of extractable (non-structural) iron generally show a low intercalating ability.

Various triphormic dioctahedral minerals and their dehydroxylation and rehydroxylation products have been examined by chemical, thermal, X-ray and infra-red absorption techniques. Since minerals with high Al-for-Si substitution do not rehydroxylate readily under the mild conditions used, attention was focused largely upon pyrophyllite and montmorillonite. Rehydroxylation occurs rapidly at about 400–500°C. Infra-red spectra indicate that there is a structural resemblance between the layers of all the dehydroxylates and that the rehydroxylates possess regions similar to untreated pyrophyllite. X-ray results show that stacking of the layers cannot be identical in the various samples. Although the structures could not be determined, the scheme proposed by Jonas for the rehydroxylate could not be reconciled with experimental results: nor does rehydroxylated montmorillonite resemble the abnormal form.

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.

Scanning electron microscopy revealed that the organization of the interstitial micaceous mineral in the title sandstones depended on the manner of drying of the specimen. After air- and freeze-drying, the lath-like mineral tended to occur as mats densely packed against the pore walls, whereas after critical-point drying an open tangled web of very long, thin ribbons virtually filling the pore space was observed (this arrangement is the one most likely to occur in situ). The ends of these filamentous ribbons often appear to be bedded in authigenic quartz overgrowths on sand grains, thus anchoring them firmly in the pores. From transmission electron microscope observations, the individual laths were frequently only 2–3 nm thick and, from electron diffraction patterns, elongated along the a-axis: the stacking modification is 1M. X-ray diffraction patterns are those that would be expected from a fully-ordered interstratified mica-smectite containing ∼20% smectite layers. It is difficult to reconcile this with the thickness as observed under the transmission electron microscope, but a possible explanation is that the ‘smectite’ interlayers in reality represent spaces between individual crystals which formed when they sedimented into an oriented aggregate.

An empirical method to estimate rapidly both mean total layer charge and location of charge in smectites and vermiculites is presented, involving exchange with a long-chain alkylammonium ion before and after the Greene-Kelly test. The method utilizes an empirically determined relationship between XRD basal spacings and the mean layer charges calculated from the conventional n-alkylammonium ion-exchange technique using simple linear regression models to describe the relationships for both monolayer-bilayer and bilayer-pseudotrimolecular layer transitions. The method provides a rapid estimation of these charge parameters and facilitates the proper identification of both smectites and vermiculites consistent with the AIPEA criteria for classification based on total layer charge. It is considered superior to conventional methods of differentiation based mainly on expansion and collapse behaviour.

Mechanically-prepared binary mixtures of two dioctahedral smectites (of different chemical compositions) with two kaolinites (with different amounts of structural defects) were studied by infrared (IR) spectroscopy to verify the ability of IR spectroscopy to detect small amounts of individual components in the mixtures. The same samples were analysed by X-ray diffraction (XRD) in transmission and reflection geometries to compare the sensitivities of these techniques. Infrared spectroscopy is suitable for detecting small amounts of kaolinite in the smectite-rich samples but is not sensitive to small amounts of smectite in kaolinite-rich samples. The IR spectra of kaolinite/ smectite mixtures have a ‘strongly kaolinitic character’ even with only 30% kaolinite. The most characteristic band of kaolinite, near 3695 cm–1, gradually decreased in intensity with decreasing kaolinite content though the presence of this absorption allowed 0.5 mass % of both kaolinites to be detected in their mixtures with smectites. On the other hand, XRD powder techniques are much more adept at detecting low smectite contents in kaolinite-rich samples.

The location of iron in five deferrated soil kaolinites and several reference samples has been investigated using chemical analyses, acid dissolution and electron paramagnetic resonance spectroscopy.

The iron of most of the kaolinites can be divided into a 'structural iron' content, measured by the amount of iron, dissolved at the same rate as aluminium by acid attack, and a 'resistant iron' content, which is concentrated with the residues.

Integration of the geff~4 resonance bands of the electron paramagnetic resonance (EPR) spectra allows a semiquantitative estimate of the 'structural iron' in the samples. A multiple relationship seems to exist between the crystallinity index, the 'structural iron' content and the shape and intensity of both geff~4 and geff~2 EPR signals. The tropical soil kaolinites are a peculiar category with a high content of iron (>2% structural Fe2O3) fire-clay kaolinite, low crystallinity and a specific EPR spectrum exhibiting strong geff~4 resonance bands and no or weak geff~2 sharp doublet.

Mg-silicate minerals (e.g., stevensite, kerolite, talc, sepiolite) play an important role in the construction of facies models in lacustrine and peri-marine environments because they are sensitive to changes in solution chemistry. However, the response of Mg-silicate mineralogy to changing aqueous chemistry is only broadly understood because the mechanisms underpinning the coprecipitation of Mg2+ and SiO2(aq) from surface water, and subsequent Mg-silicate crystallization, are unclear. Here we describe the results of experiments designed to systematically examine the effects of pH, Mg/Si and salinity of the parent solution on the nature of initially precipitated products. Structural interrogation of the products with X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and thermal analysis (TGA/DTA) allow comparison of synthetic products with naturally occurring crystalline counterparts. In general, Mg2+ and SiO2(aq) co-precipitation and nucleation of Mg-silicate layer structures first involves the rapid formation of 2:1 layers with trioctahedral occupancy and a mean coherent X-ray scattering domain between 1–2 unit cells with respect to the c axis. Well defined but diffuse hk reflections indicate two-dimensional growth, turbostratic stacking and highly variable interlayer hydration. Diffuse reflectance FTIR shows numerous structural similarities with stevensite, kerolite and sepiolite. However, TGA/DTA analysis indicates the presence of variable kerolite/stevensite interstratification not readily detectable through XRD analyses, as well as a significant degree of surface and interlayer hydration (e.g. 15–20 wt.%).

We observe a number of clear trends in the products with respect to solution chemistry. For example, at low salinity, kerolite-like products dominate at high Mg/Si and high pH, whereas sepiolite-like products are formed at lower pH and lower Mg/Si. At high salinity and high Mg/Si, stevensite-like products are favoured at high pH and kerolite-like products dominate at lower pH, whereas a decrease in Mg/Si of the solution leads to sepiolite-like products at low pH and only stevensite-like products at high pH. Higher pH leads to an increase in octahedral vacancies which favour stevensite-like products; this may result from a higher rate of two-dimensional tetrahedral sheet expansion relative to the octahedral sheet, as inferred from studies of silica oligomerization and brucite growth kinetics.

Together, our results indicate that the neoformation of Mg-rich silicates from solution may often begin with the rapid nucleation of hydrated 2:1 layers. Subsequent dehydration leads to progressive layer stacking order and could occur in response to wetting/drying cycles, prolonged exposure to high salinity solutions, or burial and heating. The surface and interlayer water associated with these products is undoubtedly an important source of diagenetic water in Mg-silicate-bearing successions, and the chemistry of this water upon later diagenesis should be a focus of future investigation.

The adsorption of methylene blue (MB) from aqueous solution on Laponite (a synthetic 2:1 layer-silicate) exchanged with Na+, Cs+ and tetraethylammonium ions has been studied. At low loadings the monomer form predominates, but as the loading increases dimers and trimers (or higher aggregates) are formed, the latter being the most important species when the loading is equal to, or larger than, the Na+-CEC. The distribution of the molecules over the surface is time-dependent due to changes in the aggregation of the clay particles. On Cs+-Laponite, and to a lesser extent on Na+-Laponite, a small amount of MB is protonated by cation-coordinated water molecules. In similar work where adsorption was from ethanolic solution, MB is adsorbed as monomers and dimers only at small loadings and precipitates on the surface of the clay aggregates at high loadings. These precipitates can be broken up by sonication.

The effect of diagenesis on shale petrophysical characteristics is being investigated as part of a study on shale sealing capacity because of its significance for modelling hydrocarbon charge histories of sedimentary basins. Results to date indicate that diagenesis (degree of cementation and dissolution) significantly affects porosity and inter-connectivity of the nano-pores (0.3–60 nm), the pores constituting the main pore-throats for tight shales. Diagenesis causes tight shale permeabilities to vary over a range exceeding an order of magnitude (10−21 − 6 × 10−20m2) and porosities to vary between 1 and 12%. In addition, diagenesis significantly influences shale nano-pore resistance to collapse during compaction and burial, mainly at depth > 2–3 km, affecting hydrocarbon trapping, overpressure and sealing capacities. Dissolution tends to delay the timing of excess pressure pulses, while cementation has a reverse effect. The significance of diagenesis is reduced at shallower depths.