The proposed impact event at the end of the Cretaceous resulted in mass extinctions and subsequently significant variations in the geochemical and mineralogical composition of the sediments marking the K/T boundary. The impact-generated material derived from target rocks produced the ejecta layer deposits around Chicxulub crater, which were subsequently diagenetically altered to mainly smectite in marine sections and to kaolinite in continental sections. The fireball layer represents the cosmic dust dispersed and deposited globally and contains smectite derived from the alteration of microkrystites and the finest fraction. The lowermost Danian clay layer, recognized in marine sections, resulted from the sudden decrease in ocean productivity and represents a reduced sedimentation deposit. Its clay mineral associations depend on local environmental conditions and diagenetic processes. Overall, the diagenetic alteration of the boundary materials resulted in a significant modification of original signatures. The composition of the clay mineral phases can, however, still be evidence of the nature of the precursor materials providing evidence for an extraterrestrial impact event.

Clay minerals in early Jurassic sequences of shales, siltstones and sandstones deposited in non-marine, transitional and shallow marine environments have been examined by X-ray diffraction, electron microscopy and chemical analysis to study the relationship between clay minerals, their environment of deposition and subsequent diagenetic modifications.

The inherited clay mineral composition of the fine-grained sediments reflects the influence of climate, relief, source rocks and depositional processes. Inhomogeneous clay mineral assemblages, comprising abundant kaolinite and varying proportions of illite, I-S, chlorite and vermiculite, characterize fine-grained sediments from the non-marine and transitional environments. In shallow marine depositional environments clay mineral assemblages are more uniform, dominated by illite+I-S with minor kaolinite and chlorite.

The principal diagenetic process affecting fine-grained sedimentary rocks is the smectite–illite transformation. In sandstones, the authigenic formation of kaolinite, chlorite and illite appears to have been primarily determined by the environment of deposition.

Illite-smectite (I-S) mixed-layer minerals from North Sea oil fields and a Danish outcrop were investigated to determine the detailed structure and the diagenetic clay transformation. Clay layers in the chalk and residues obtained by dissolution of the chalk matrix at pH 5 were investigated. The phase compositions and layer sequences were determined by X-ray diffraction (XRD) including simulation with a multicomponent program. The structural formulae were determined from chemical analysis, infrared (IR) and 27Al NMR spectroscopies and XRD, and the particle shape by atomic force microscopy (AFM). A high-smectitic (HS) I-S phase and a lowsmectitic (LS) illite-smectite-chlorite (I-S-Ch) phase, both dioctahedral, together constitute 80 – 90% of each sample. However, two samples contain significant amounts of tosudite and of Ch-Serpentine (Sr), respectively. Most of the clay layers have probably formed by dissolution of the chalk, but one Campanian and one Santonian clay layer in well Baron 2 may have a sedimentary origin. The HS and LS minerals are probably of detrital origin. Early diagenesis has taken place through a fixation of Mg in brucite interlayers in the LS phase, this solid-state process forming di-trioctahedral chlorite layers. During later diagenesis involving dissolution of the HS phase, neoformation of a tosudite or of a random mixed-layer trioctahedral chlorite-berthierine took place. In the tosudite, brucite-like sheets are regularly interstratified with smectite interlayers between dioctahedral 2:1 layers, resulting in ditrioctahedral chlorite layers.

The amorphous aluminosilicate allophane was synthesized by rapid mixing of inorganic solutions with high initial concentrations (10 – 100 mmol/l) followed by hydrothermal treatment. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed homogeneous products having a hollow spherical amorphous structure with a particle diameter of 3 – 5 nm. The amorphous products had a high BET specific surface area (490 – 552 m2/g) in comparison with natural allophane and had a narrow pore-size distribution (2 – 5 nm in diameter). The results of water vapour adsorption isotherm studies showed a gradual increase over the range of relative water vapour pressure of 0.6 – 0.9 and reached a maximum of ∼85 wt.%. The synthetic allophane shows promise as an adsorbent material because of its high adsorption-desorption capacity and its unique structure.

Illitic-smectitic clays were matured with a ferruginous, bicarbonate-rich and sulphate-rich water for different periods of time (7, 15, 30, 60 and 90 days), and subjected to discontinuous stirring, to test their use in pelotherapy. A progressive degradation of the clay minerals was observed during the maturation process, with a reduction in the illite and smectite crystallinity, in the percentage of smectites and in the phyllosilicate content. The percentage of <2 μm particles also decreased. These modifications caused changes in the clays’ physicochemical properties, which are evident in an increase in their plasticity index and in slower cooling of the peloid, both of which improved the clays’ effect in pelotherapy.

The morphological and structural changes in smectite caused by hexadecyltrimethylammonium (HDTMA) treatment were studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The HDTMA-exchanged smectite shows not only morphological features such as irregular, wavy surface with curled edges, but also structural features such as large d-spacings (20 – 26 Å ) and lattice distortions. The surface morphological heterogeneity is assumed to be related to the inhomogeneous intercalation of HDTMA cations into the interlayer of smectite.

Six smectites of different tetrahedral and octahedral compositions (SAz-1, Chambers, Belle Fourche, two subsamples of nontronite 33B and SWy-1) were Cs-exchanged and submitted to 70 wetting-and-drying cycles. X-ray diffraction (XRD) of oriented and glycolated mounts of the resultant material showed non-expandable layer proportions ranging from 15 to 60%. They were also analysed by powder XRD at 200°C in vacuum. These patterns showed that 15 – 40% of the layers were not rotated relative to each other and the rest were randomly rotated (no rotations of the 60° and 120° types). All layers had a d-spacing of 11 Å, corresponding to collapsed layers with Cs in the cavities created by the hexagonal rings of the tetrahedral sheets. Analysis of the number of cavities available in relation to the layer rotation shows that the rotation angle must be close to 30° or its multiples 90, 150, 210, 270 and 330°. X-ray diffraction and thermal analysis detected the same proportion of cis-and trans-vacant sites in the smectites. The ideal bdimensions of the tetrahedral and octahedral sheets (the sheets are considered independently, without deformation) were calculated for the samples used in this work and for others from the literature, using the tetrahedral and octahedral compositions. These ideal bdimensions have a strong positive correlation. The cis/transvacant character of the smectites is related to the relative lateral dimensions of the ideal tetrahedral and octahedral sheets. A possible explanation of this fact is offered, in which the different configurations of hydroxyls and oxide ions in cis- and trans-vacant structures can affect octahedralsheet dimension.

X-ray powder diffraction patterns of halloysite (7 Å) are characteristically altered following solvation with ethylene glycol. Some effect was first noted in the classic work of MacEwan but its value in the unequivocal identification of halloysite (7 Å ) seems to have been overlooked subsequently. The response to ethylene glycol solvation involves a decrease in the intensity (peak height) of the peak at ∼7.2 Å and an increase in the intensity (peak height) of the peak at ∼3.58 Å thus narrowing the 7.2 Å /3.58 Å peak height intensity ratio. For pure samples of halloysite, this ratio is narrowed by an average of ∼50%. This distinctive change is related to the interstratified nature of halloysite (7 Å), specifically the presence of ‘residual’ interlayer water, i.e. halloysite (10 Å), which can be replaced with ethylene glycol so forming 10.9 Å layers, a spacing that is almost exactly one and a half times the thickness of dehydrated (7.2 Å) layers which do not imbibe ethylene glycol. Thus the separation between the 001 peaks in the 7.2 Å /10.9 Å interstratification is increased and the 0027.2 (3.58 Å) and 00310.9 (3.63 Å) peaks become more or less coincident, compared to the 7.2 Å /10 Å interstratification, i.e. the partially hydrated state. The widespread use of ethylene glycol solvation in clay mineral studies makes it a particularly useful and simple test to determine the presence of halloysite. Pure halloysites should be readily identifiable and experiments indicate a ‘routine’ sensitivity of ∼20% halloysite in mixtures with kaolinite, although this will depend on factors such as ‘crystallinity’ and could be improved with careful attention to intensity measurements. It is proposed to call this phenomenon the ‘MacEwan effect’ in honour of its discoverer Douglas Maclean Clark MacEwan.

Tritium accumulation in clay minerals (kaolinite, montmorillonite, palygorskite) was studied experimentally over a one year contact with tritiated water (initial activity 1.676x109 Bq/m3) under room conditions, and was compared to theoretical calculations. The amounts of tritium ions in bound water and structural hydroxyls were measured by the activity of water fractions released at characteristic temperatures determined on the basis of the mineral DTA patterns. Experiments showed that after a 400 day contact with tritiated water, tritium exchange rates (θ) were highest in palygorskite (θa = 0.42 in bound water and θs = 0.51 in the structure) compared to montmorillonite (θa = 0.15 and θs = 0.11, respectively) and kaolinite (θa = 0.34 and θs = 0.02, respectively). This could be due to different tritium concentrations in the solution near the bound-water layers, and also to certain features of the mineral structures, most of the kaolinite structural hydroxyls not interacting directly with bound HTO molecules.

Tritium accumulation in these minerals, under room conditions, can be described by a relatively simple two-stage isotope exchange model in which tritium ions first migrate from the solution to the bound layers and then substitute the protons of the structural hydroxyls. Rate constants for both stages of this isotope exchange were calculated on the basis of the experimental data.

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.

Three raw samples of Fe-rich smectites from Gafsa (Jebels Shemsi and Hammadi, Tunisia) have been characterized by different techniques which indicate that they contain (15 – 20%) illite, probably interstratified and to a lesser extent they also contain kaolinite, calcite, quartz and Fe oxides. These samples present a relatively high Fe content (∼9%) in the <2 μm fraction. From EPR and Mössbauer spectroscopy it is deduced that Fe is mainly present as Fe(III) in the octahedral environment of smectites and also in Fe-oxyhydroxides associated with the clays. Aluminium-pillared clays have been prepared from the Na+-purified samples, and their thermal stability and acidity have been studied.

The surface properties of various synthetic layered silicates, Na-kanemite, Nakenyaite and magadiite, exchanged with H, K and Ca, were examined using high-resolution nitrogen and argon adsorption and the data were treated using the Derivative Isotherm Summation method. Using argon as an adsorbate, the aspect ratio of platelets can be determined. In the case of magadiite exchanged with various cations, the stacking of particles is influenced by the nature of the exchangeable cations, thicker platelets being observed for ions with low polarizability. Highresolution argon adsorption data also confirm some structural information previously deduced from Raman spectroscopy experiments concerning the existence of rather open six-membered rings at the surfaces of both magadiite and kenyaite. Furthermore, in the low-energy domain of the isotherms, argon forms a very organized film on basal planes, suggesting a commensurate relationship between silica framework and argon atoms for both magadiite and kenyaite, contrary to what is observed for kanemite. Nitrogen adsorption results reveal the presence of polar sites on the surface of all the investigated minerals but does not allow us to propose an unequivocal assignment for such sites.

A series of reduced-charge montmorillonites with cation exchange capacities of 89, 73, 49 and 29% of the starting mineral was prepared from a Li-saturated smectite (Kriva Palanka, Republic of Macedonia) by heating at 110, 130, 160 and 300°C for 24 h (samples KP110 – KP300, respectively). Hydration properties of this series were investigated gravimetrically and by in situ XRD at different relative humidities (RHs). In the gravimetric experiments, higher water contents were observed for desorption than for sorption and hysteresis was present over the whole range of RHs for all the samples. The parent montmorillonite and the samples KP110 and KP130 retained similar amounts of water under the same conditions, thus showing that the decreased negative charge on the layers had minor effect on the water uptake at all investigated RHs. Significantly decreased water content was retained by KP160 while KP300 contained only 8% water at 100% RH. The d001 values of the parent montmorillonite and the samples KP110 and KP130 increased with RH, while those of KP160 and KP300 were independent of RH and remained at ∼10.4 and ∼9.6 Å, respectively.

We have investigated the adsorption of D- and L-alanine, and their respective dimers, by three allophanes with different Al/Si ratios. The Kanuma (Al/Si = 1.2) and Kitakami (Al/ Si = 1.5) allophanes were from Japan whereas the Te Kuiti (Al/Si = 1.6) sample came from New Zealand. The three allophanes differed in their capacity for adsorbing alanine but none of the samples showed a clear preference for either the D- or the L-form. In the case of alanyl-alanine both Kanuma and Kitakami allophanes gave a hint of preferring the L- to the D-enantiomer. On the other hand, the allophane sample from Te Kuiti showed a clear preference for L-alanyl-L-alanine. In keeping with this observation, circular dichroic spectrometry indicated that solutions of a racemic mixture of alanyl-alanine, after equilibration with Te Kuiti allophane, became relatively enriched in the Denantiomer. The size, intra-molecular charge separation, and surface orientation, of L-alanyl-Lalanine zwitterions apparently combine to confer ‘structural chirality’ to the complex (adduct) with Te Kuiti allophane. As a result, the mineral-organic complex develops a preference for the L-form of alanyl-alanine. This finding points to a possible role of certain allophanes in the origin of biochirality.

A series of kaolin-rich mineral samples was treated with hydrofluoric acid (HF) and the residual material characterized using infrared (IR) spectroscopy, supplemented by scanning electron microscope (SEM) observations. By examining the hydroxyl-stretching region of the IR spectra before and after treatment with hydrofluoric acid, it was possible to identify the three kaolin polytypes – kaolinite, dickite and nacrite – with greater certainty. The SEM observations suggested that the rate of dissolution of the kaolin phase was largely dependent on particle size. In general, dickite and nacrite tend to occur in the coarser clay fractions, and for this reason the finer-grained kaolinite is preferentially dissolved by the HF treatment. However, in the Keokuk kaolinite, which occurs in exceptionally large particles, it was still possible to concentrate a dickitic fraction by HF treatment, suggesting that in some cases kaolinite may be more susceptible to HF dissolution for reasons other than particle size. The IR spectra of disordered kaolinite could be interpreted as arising from a mixture of kaolinite and dickite components. However, both components dissolve at the same rate in HF, supporting the idea that disordered kaolinite consists of an intimate association of randomly stacked dickite-like and kaolinite-like components.