The smectite to illite transformation in early Miocene sediments was studied in wells and outcrops in the western Pannonian Basin, where magmatic activity caused very high Miocene heat flows (250-400 mW/m2). Although the thermal history is similar, large differences in smectite to illite diagenesis were observed. (1) The boundaries between early/middle and middle/late diagenesis in two wells (Pichla, Radkersburg) and the Maribor area correspond to vitrinite reflectance values of 0.4-0.8 and 1.1-1.5% Rr. Anchimetamorphism starts at ~2.1% Rr. In spite of magmatic heating, the smectite to illite transformation can be modelled using kinetic data proposed for areas with a 'normal' burial diagenesis. (2) Smectite to illite reactions are advanced compared to vitrinite reflectance in the Ribnica-Selnica Trough. This is probably related to fluids with elevated K+ concentrations. (3) Clay mineral alterations lag behind coalification significantly in the Mitterlabilt well. These different correlations indicate that clay mineral thermometry should be used with caution and that factors other than temperature and time can influence clay mineral reactions.

Fixed nitrogen in illite-smectites (I-S) has been measured for Miocene shales from a Gulf of Mexico oil well. Fixed N values for the <0.2 µm fraction increase with depth from 150 ppm (1000 m) to a maximum of 360 ppm (3841 m). This increase is coincident with illitization from 41% I in I-S to 75% I in I-S. Below 3841 m, fixed N values decrease to 190 ppm (4116 m) while I-S is maintained with a slight increase from 77 to 82%. The changes in fixed N with increasing illitization are consistent with the notion that illitization proceeds via both transformation and dissolution/ precipitation reaction mechanisms. The trend of decreasing fixed N in illitic I-S is compatible with surface-controlled crystal growth and Ostwald ripening mechanisms for illitization. The trend may also be linked to the timing of maximum NH] release from kerogen maturation during oil generation. The changing rate of NH+4 liberation from organic matter and multiple illitization reaction mechanisms can result in complex N geochemical cycling pathways throughout early diagenesis to metamorphism.

Glauconite and Ca phosphate peloids occur in Jurassic and Cretaceous bioclastic carbonate rocks from pelagic swell sequences of the Algayat-Crevillente Unit (Subbetic Zone). The size and morphology of the peloids are controlled by the bioclasts. The glauconite in both stratigraphic positions is K rich (>0.69 atoms p.f.u.) and shows well-defined 10 Å. lattice fringes. Poorly crystalline areas with a composition of Fe-smectite are found within the peloids, indicating the nature of the glauconitic precursor. This precursor would be formed in the shielded microenvironments of the bioclast and later transformed to glauconite by equilibration of peloids with sea water that culminated with the crystallization of a phosphatic phase. The greater presence of smectite areas in the Jurassic peloids and the lower K contents (0.69-0.81) of these glauconites, compared with the Cretaceous glauconites (0.81-0.89) can be explained by the calcitic early diagenetic cementation which stopped the process of glauconitization.

Arid soils in central Iran that evolved from the weathering of post-Tethyan sediments contain palygorskite. Clay fractions of gypsiferous soils and their associated sediments from different landforms from central Iran were investigated. Palygorskite was the dominant silicate clay mineral in clay fractions of the soils, and of Oligo-Miocene limestone, a less common parent rock. The Jurassic shale and Cretaceous limestone contain illite and chlorite with a trace amount of palygorskite. Association of large amounts of palygorskite bundles with gypsum in the gypsiferous soils studied, supports the hypothesis that palygorskite was probably formed after the initial precipitation of gypsum, that created a high pH and Mg/Ca ratio. The major portion of the palygorskite present in colluvial and plateau soils was probably formed authigenically when central Iran was covered by post Tethyan shallow hyper-saline lagoons. Palygorskite in alluvial soils appeared to be essentially detrital.

A new method of measuring the layer charge of smectites by IR spectroscopy is proposed based on the integrated intensity measurement of the band assigned to the ammonium fundamental ν4 mode of NH+4-exchanged clays. Measurements are made before and after Li fixation (Hofman & Klemen effect). These allow the quantitative determination of the total charge, equivalent to CEC, and tetrahedral and octahedral charge distribution in both dioctahedral and trioctahedral smectites.

Four samples of <2 µm fractions of Fe-rich bentonites from tile area of the Zvolenská kotlina Basin (Slovakia) have been investigated by MiSssbauer spectroscopy and reductive dissolution in ammonium hydrogen oxalate (pH = 2.7). Both methods have shown the presence of goethite in the samples. The relative amount of Fe bound in goethite varied more within the samples of bentonite from Zvolensk~ Slatina, which was redeposited after transport over a short distance, than in the authigenically altered bentonite from Hrochot’. The results of the fits of the reductive dissolution curves suggest size distribution, variation in Al-for-Fe substitution in goethite particles and/or different access of extracting solution to goethite particles present in the analysed fine fractions of bentonites.

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 kinetics of structural change of a highly ordered kaolinite intercalated with potassium acetate have been studied through both intercalation and deintercalation. Deintercalation of the intercalated kaolinite, brought about by washing for different time intervals was followed by both X-ray diffraction and Raman microscopy. X-ray diffraction shows the kaolinite to be highly ordered with a Hinekley index of 1.42 and intercalated to ~90%. X-ray diffraction also showed that the intercalated kaolinite was deintercalated by 80% in the first minute of washing. An additional Raman band, attributed to the inner surface hydroxyl groups, strongly hydrogen bound to the acetate, is observed at 3605 cm-1 for the potassium acetate intercalate with the concomitant loss of intensity in the bands at 3652, 3670, 3684 and 3693 cm-1. Upon deintercalation, the intensity of the 3605 cm-1 band decreased as the 3695 cm-1 band increased. The Raman spectral changes brought about upon deintercalation mirrored the changes observed by X-ray diffraction. Deintercalation of kaolinite caused disordering of the kaolinite.

This paper aims at characterizing the structural and textural evolution of three mixed-layered clays in Ca-form from Southern and Central Tunisia, These samples contain various amounts of mixed-layer smectite-illite associated with crystallites of kaolinite. The clay fractions were prepared in the Ca-form and submitted to suction pressures increasing from 3.2 up to 1000 kPa. The structural and textural changes of the pastes obtained were studied by TEM and SAXS. The TEM observations and SAXS quantitative analysis on samples at low stress (3.2 kPa) showed that the thickness of the particles (number of layers per particle) and their lateral extension (in the plane of layers) decrease with increasing illite content. The textural evolution during drying, as described by SAXS, is controlled by the geometry of particles which is determined by the mineralogy of the structural units. With increasing illite content, the particles became shorter, rigid and had flat surfaces. This geometry increases their ability to associate face-to-face during dehydration. When the 2:1 fraction contains a high proportion of smectite, the architecture of the clay-water system at high water content (low stress) seems to be analogous to that of smectites. However, contrary to the behaviour of pure smectites reported in the literature, desiccation led first to a rupture of particles and a reorganization of the geometry of the pore system. This behaviour is due to the rigidity of particles caused by the presence of non-exchangeable K. The structural evolution showed that for an illite-rich sample a transition from the three-water layer to the one-water layer state occurred at 1000 kPa, whereas for smectite-rich materials, the hydration state of layers, i.e. three water layers, was not affected.

The observation of clayey matrix on a thin-section under polarized transmitted light allows the analysis of the clay particle arrangements, the measurement of their orientations in 3-D, and finally the cartography of the different orientation modes by using a simple image analysis system connected to the optical microscope. The method is based on: (1) the analysis of the shape evolution of the grey-level diagram vs. the rotating stage angles; and (2) the mathematical decomposition of these grey-level diagrams into elementary gaussian curves. For each identified orientation mode, the standard deviation of the grey values gives the dispersion index of the oriented particles around the axial plane. The 3-D representation is performed on the Wulff stereonet. The horizontal orientations are measured by simple rotation of the revolving stage and the dip angles are deduced from the peak displacements along the abscissa of the grey-level diagram during the complete rotation of the revolving stage. The quantifications (percentage, isotropy and distribution index) are performed after a thresholding operation of each orientation mode.

Intercalation of the tris(2,2'-bipyridine)ruthenium(II) complex cation into a layered silicate (magadiite; the ideal formula for which is Na2Si14O29.nH2O) was investigated. Since the complex cation did not intercalate by a direct ion exchange reaction with the interlayer Na ions in an aqueous medium, dodecyltrimethylammonium exchanged magadiite was used as a precursor. Depending on the loading of the complex cations and the solvents employed for the reactions, two types of tris(2,2'-bipyridine)mthenium(II)-magadiite intercalation compounds formed. One has a basal spacing of ~2.9 nm due to a large amount of the dodecyltrimethylammonium ions which remained in the interlayer space of magadiite and coexisted with the intercalated tris(2,2'- bipyridine)ruthenium(II) complex cations. The other has a basal spacing of '2.0 nm because the intercalated tris(2,2'-bipyridine)ruthenium(II) complex ions form a monolayer in the interlayer space of magadiite.

The swelling behaviour and hydraulic conductivity of Na-bentonite powder and bentonite-sand mixtures (10 and 20% of bentonite by dry weight) have been measured with distilled water and various salt solutions (0.01, 0.1 and 1 mol/l concentrations), It was found that in dilute solutions, the bentonite in mixtures subjected to small confining stresses swells sufficiently to separate the sand particles and reach a clay void ratio similar to that achieved by bentonite alone. At high stresses, or in strong solutions, the bentonite in a mixture has insufficient swelling capacity to force the sand particles apart and swelling is limited by the sand pore volume. The hydraulic conductivity of a mixture depends on the bentonite void ratio, and the porosity and tortuosity of the sand matrix. A design model is proposed to predict the engineering properties of a mixture over a range of confining stresses from the properties of its constituents and the permeant.

Talc [ideal formula: Mg3Si4O10(OH)2] is one of the classical 2:1 trioctahedral phyllosilicates that has been analysed intensively with respect to its formation, thermal stability, chemical properties and structure (e.g. Wilkins & Ito, 1967; Rayner &Brown, 1973; Ward, 1975; Martin et al., 1996). Single crystal structure refinement by X-ray diffraction (XRD) showed clearly that talc is triclinic and crystallizes in the space group CI (e.g. Rayner & Brown, 1973; Perdikatsis & Burzlaff, 1981). Based on this structural model, two coordination arrangements of OH groups to Mg in the octahedral sheets can be deduced. Since XRD data give only an insight into the average structure, local information on the ligand field of the cations is limited. Currently, no analytical tool is known to determine directly the ligand field of Mg in the octahedral sites.

A recent article by Refait & Génin (1997) was devoted to Ni(II)-Fe(II)-Fe(III) pyroaurite-like hydroxychlorides obtained by aerial oxidation of mixed Ni(II)-Fe(II) hydroxides with various P = Fe/Ni ratios in chloride-containing aqueous solutions. Corresponding to the ideal composition Ni3-xIIFexIIFeIII(OH)8Cl.nH2O , the Fe(III)/[Ni(II)+Fe(II)] ratio is 1/3 when P is >1/3. These hydroxyehlorides oxidize quickly and the final product depends on P. In the absence of nickel, P = ∞, FeII3FeIII(OH)8Cl.nH2O, known as Green Rust one (Bemal et al, 1959) oxidizes into γ-FeOOH. When P is >5/3, the X-ray diffraction (XRD) analyses of the end-product reveal lepidocrocite and some Ni(II)-Fe(III) hydroxychloride.

Outcrop samples of Ordovician K-bentonite from northeast Georgia were studied with X-ray diffraction (XRD) using different cation saturations to look for possible redistribution in layer charge. It was noted that XRD patterns of the samples responded uniquely to each cation treatment. The purpose of this note is to demonstrate a refinement to the method of Środoń (1980) for the precise identification of mixed-layer illite-smectite (I-S) and to note the importance of using several homoionic saturations in the interpretation of the XRD patterns.