The mineralogy of the Neogene lacustrine facies of Pelitçik basin was investigated for the purpose of deriving the palaeoenvironmental parameters of this intervolcanic basin. The laboratory studies indicate that dolomite and K-feldspar are the major non-clay minerals in the study area, where plagioclase, analcime, fibrous zeolite and quartz are the minor constituents. Dolomites are found to be non-stoichiometric in chemistry. The clay fraction of the lacustrine facies is composed mainly of dioctahedral smectites. The smectites are rich in Al-Fe indicating a detrital origin. Illite comprises a minor contribution to the clay fraction, where chlorite and kaolinite are found in trace amounts. Based on dolomite stoichiometry and the mineral paragenesis found in the Pelitçik basin, the depositional conditions are suggested to have been a shallow, quiet, perennial lacustrine environment with fresh to slightly saline and slightly alkaline water chemistry. In addition, based on geological and mineralogical constraints, it is suggested that the water chemistry fluctuated during the deposition of the Pazar formation and the lake began its evolution with a hydrologically closed system and completed its evolution with a hydrologically open system.

Indurated volcanic soils (tepetates) of the Mexican Altiplano display thick columnar horizons, hard laminar horizons, and grey mottles at depth. X-ray diffraction (XRD) studies show a relative enrichment in cristobalite vs. halloysite in the indurated plates of the laminar horizons and in the clay fraction of the mottles. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) studies of these two soil components have shown that they are composed of small tubes of halloysite in which numerous globular grains ∼1 μm in diameter are embedded. Based on the relative abundance of cristobalite in pedological features and on the spatial relations between successive mineral phases, we interpret the cristobalite as a transformation of halloysite with a transitional amorphous phase. In the globular grains, large platy 1:1 clay minerals undergo a progressive transformation into platy particles of opal-A and opal-C. These are in turn transformed into cristobalite without further major change in their shape and appearance, except for a higher electron density than opal and clay.

Celadonite and glauconite samples heated at different temperatures were studied by X-ray and electron diffraction. For dioctahedral micas the in-plane component of the translation between layers (ccosβ/a), which is strongly dependent on the position of the vacant octahedral site, significantly decreases at temperatures greater than the temperature of maximum dehydroxylation. The simulation of XRD patterns from different structural models reveals the actual crystal structure of dehydroxylated samples as well as the dynamics of the structural transformations. In the nonheated state the samples consist of tv (trans-vacant) 2:1 layers. During dehydroxylation, cations migrate from cis- into trans-octahedra and have 5-fold coordination. In the averaged unit-cell the ‘residual’ anions formed after the dehydroxylation reaction occupy the former OH sites with probability equal to 0.5. The migration of octahedral cations is accompanied by the transformation of the C-centred layer unit-cells into primitive ones. In contrast to Fe, Al and Mg cations have a greater ability to migrate.

The quantitative interpretation of the reflection intensities of the SAED patterns of glauconites reveals the mechanism of migration of the octahedral sheet cations during heating up to 750°C. It confirms that Mg2+ has a greater ability than Fe3+ to migrate from cis-to trans-sites, as previously found by means of XRD pattern modelling. For samples heated to 650°C, the two formerly vacant trans-sites in the base-centred unit-cell become occupied, but differently, which leads to a primitive unit-cell, and the cis-sites remain filled almost entirely by Fe3+ only. The cation migration occurs through the nearest shared edges in the [010] and [310] directions. The samples heated to 750°C reveal a base-centred super-cell with A = 3a and B = b. All Mg cations leave the cis-sites to occupy completely four of the six available trans-sites of the super-cell. Migration also occurs through the shared edges in the [010] and [310] directions. The primitive unit-cell is not an intermediate step in the migration process leading to the super-cell. The existence of additional satellites in the SAED patterns of some crystals heated to 750°C corresponds to the existence of antiphase domains with a 3b/2 width and an antiphase shift of a/2.

The alteration and transformation behaviour of the Tertiary Hammerschmiede Smectite and the Jurassic Opalinus Shale in an alkaline solution was studied in column experiments. The Hammerschmiede Smectite is proposed as potential backfill material and the Opalinus Shale as host rock for the Swiss low-level nuclear waste storage site. Over a period of 18 months, the evolution of permeability, pH and solution concentrations were measured. After the experiment, the columns were cut into pieces to study the mineralogical and the chemical evolution of the clays. X-ray diffraction (XRD) revealed no significant appearance or disappearance of diffraction peaks at the end of the experiments. The scanning electron micrographs of the clays revealed that both clays exhibited a precipitation zone, which extends from 0 to 2 cm below the infiltration surface. Both clays showed significant differences in the evolution of pH and hydraulic conductivity. The solution front crossed the Opalinus Shale column entirely after only 11 weeks and the initial values for K+ and Na+ were conserved in the solution. For both clays, the salt concentrations in the percolating fluids mirror the evolution of pH.

Changes in particle organization and pore-spaces with applied mechanical and hydraulic stresses were followed using TEM, SAXS mercury porosimetry and gas adsorption for two Na-smectites, Laponite and hectorite, with similar structural formulae but different particle sizes. The TEM images show that hectorite has particles larger and more anisotropic than those of Laponite. The particles order perpendicularly to the direction of axial mechanical stress and become disoriented under hydraulic stress. According to the SAXS results, Laponite is composed of 1 – 3 small layers and hectorite of more compact (10 – 80 layers) particles. In Laponite, mechanical stress strongly reduces the amount of macropores but does not affect micropores and mesopores; hydraulic stress increases the macropores. In hectorite, the pore-volume is lower than in Laponite. The different techniques used yield complementary results and show the considerable effect of layer dimension on the behaviour and microtexture parameters of smectite submitted to hydromechanical stresses.

The localization and number of the different types of water in two Na-smectites (Laponite and hectorite) were studied as a function of the hydromechanical stresses applied. Water volume variation was obtained by macroscopic oedometric tests. Thermogravimetric analysis (TGA), X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) were used to study water-smectite interactions. The TGA results show that the bulk water content decreases while the adsorbed water content remains practically constant with increasing mechanical stress; hectorite adsorbs less water than Laponite at low hydraulic stress. The proportion of adsorbed water obtained by NMR confirms the TGA data. The interlamellar space and the equivalent water layers decrease with increasing mechanical stress and is always lower in hectorite than in Laponite. Hydromechanical effects on the water-Na-smectite system are in agreement with microtexture changes measured by porosimetry. Differences in the properties of the two clays can be attributed to the higher extension of the layers in hectorite compared with Laponite.

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.

Metakaolins formed by total dehydroxylation of kaolinite, dickite and nacrite were hydrothermally treated at 240°C, for 2, 21 or 182 days, at initial pH = 5– 6 or 1. Kaolinite was the only mineral of the kaolin subgroup crystallized in these treatments. Kaolinite is less ordered for pH = 4– 6 than for pH = 1. This can be attributed to the influence of specific chemical, morphological, and/or crystalline properties of the metakaolins. Two different processes of kaolinite formation and crystal growth must be involved depending on the pH and metakaolin. The first process implies the dissolution of the metakaolin and crystallization of thin prismatic or dendritic kaolinite particles which curl, probably due to surface tension. The second process implies the rapid formation of small pseudohexagonal kaolinite particles which would aggregate and coalesce to form bigger particles.

A structural model is proposed for illite-smectite (I-S) from diagenetic environments which accounts for the presence of three different layer types which are defined as follows: montmorillonite (low-charge, octahedrally substituted, fully expandable), vermiculite (high-cha rge, octa- and tetrahed rally substitut ed, only partly expandabl e) and illite (K0.9Si3.3Al0.7R1.83+R0.22+O10(OH)2). All three layers may be found within the MacEwan crystallites, whereas external edges of the crystallites are only vermiculitic during the illitization process. In the proposed model, a layer is defined symmetrically on each side of the interlayer space, leading to the existence of polar 2:1 units. It is proposed that the I-S growth is a three step mechanism: (1) formation, from sediments of variable composition, of montmorillon ite crystallites; (2) vermiculitization of the montmorillonite crystallite interfaces and of inner montmorillonite layers; and (3) precipitation of illite of fixed chemical composition. The I-S crystal grows by addition of illite layers linked by K+ or NH4+ ions saturating the vermiculitic interfaces.

Observations of natural minerals and experimental run products show that I-S (illitesmectite mixed-layer minerals) with a high illite content as well as pure mica-illite crystallites can have a lath shape (aspect ratio >3). This shape is common to the I-S minerals under a variety of conditions of formation. The experiments presented indicate that the occurrence of lath-shaped micaillite is due to a slow growth rate from supersaturated solutions. This lath-shaped crystallite is metastable as the ultimate stable shape is hexagonal. A longer period of crystal growth will replace the mica-illite laths with crystallites of a hexagonal form. Thus the presence of lath-shaped micaillite indicates the existence of a metastable crystal form for this mineral.

Illite age analysis (Pevear, 1992) and similar mixing methods demonstrate nearlinear behaviour when corrected for smectite content in illite-smectite and substitutions for K+ in illite layers. Srodon (1999) found that highly curved mixing lines result from theoretical calculations and challenged the validity of IAA. However, our theoretical calculations indicate near-linear mixing lines result when corrected for the amount of smectite and known K+ substitutions (Na+ or NH4+). We conclude that perfect linearity is unattainable because IAA attempts to unmix a system linearly, but the system is based on an exponential function (K-Ar equation). In practice, we believe IAA can successfully determine the age range of illite diagenesis, even though perfect linearity is not attainable because: (1) significant deviations from linearity occur only if >500 Ma separate the diagenetic and detrital ages; (2) IAA analytical uncertainties result in diagenetic and detrital ages that span a range of ages.

As plots of K-Ar ages vs. percentage of the detrital component of mineral mixtures containing a detrital and a diagenetic illite (or illite-smectite) have different curved shapes, the linear extrapolation method of extracting the end-member ages is not justified. The curvature depends on the difference in K2O contents; thus it can be minimized if the percentage of detrital illite is normalized to the sum of detrital illite plus illitic fraction of diagenetic illite-smectite.