In the Czechoslovak part of the Upper Silesian Coal Basin (Ostrava-Karvina Coal Basin), only part of the Upper Carboniferous (Namurian A, B, C and Westphalian A) is well developed, and tonsteins, which are clayey rocks or claystones, occur as thin, clayey interlayers in the coal seams. Two types of primary volcanic mineral assemblages were identified in four tonstein samples from different coal seams; the first type is characterized by the presence of biotite and sanidine, and the second by the presence of biotite, bytownite and Ca-amphibole. All tonsteins studied contained kaolinite minerals, volcanic quartz grains, crystals of zircon and apatite. Separated biotite flakes with an admixture of kaolinite layers were identified as 1M polytype. The flakes without kaolinite minerals were identified as epitactic overgrowth of 1M and complex polytypes, and twinned crystals of 2M1 polytype. Kaolinization of biotite flakes was observed in all tonstein samples studied. Kaolinite single layers (7 Å) as well as two-layer polytype of kaolinite minerals (14 Å) sandwiched between biotite layers (10 Å) were identified by HRTEM imaging.

Sudoite occurs as a cryptocrystalline clay in some Visean K-bentonites from Belgium. Usually associated with illite-smectite mixed-layers, this chlorite has been found locally as a monomineralic clay component of a K-bentonite bed. The mineral has a composition close to (Al3Mg2)(Si3Al)O10(OH)8. The cell parameters have been calculated from the diffractogram using the space group C2/m (a = 5·228, b = 9·056, c = 14·326 Å, β = 97°00′, d(060) = 1·509 Å). The polytype corresponds to a IIb structure. Some hypotheses are proposed for the origin of this chlorite. The coexistence of sudoite and pyrite could explain why the chlorite present in Visean K-bentonites is not a Fe-rich species typical of diagenetic conditions, but a Fe-poor one.

Chemical and mineralogical analyses of fossil caliche profiles developed on top of Lower Pleistocene alluvial formations in the East-central sector of the Ebro basin indicate that they have high content of carbonate (average 84%) and high Ca/Mg ratios (average 136). The clay mineral assemblages vary slightly depending on the host material, and, therefore, on the alluvial formation in the source area. Inherited detrital minerals (illite, kaolinite and chlorite), transformed components (from chlorite to mixed-layers of chlorite-vermiculite, and from smectite to palygorskite) and a neoformed phase (palygorskite) have been observed. The contents of carbonate and magnesian clay minerals (smectite and palygorskite) increase from the bottom to the top of the profiles, in relation to hardpan laminated caliche facies. The amount of palygorskite is controlled by the concentration of Mg2+ which in turn depends on the absolute content of Mg2+ in the host material and on its relative concentration by processes of evaporation linked to decreasing permeability in the profile during the biogenic-pedogenetic carbonate accumulation stages. These processes form part of the development of caliche profiles in a semi-arid environment.

The allophane studied occurs in the weathered zones of the barite-sulphide-bearing dolomitic levels, interbedded in the barite ore deposits of Vide de Alba and San Bias (Province of Zamora). These ore deposits are interstratified in the Silurian-Devonian sulphide bearing volcano sedimentary materials of the Alcañices Synform. The allophanic samples have been studied by polarizing microscopy, SEM, XRD, DTA, TG, IRS, EMA and chemical analyses, the last after dissolving the samples by acid (HF + HNO3 + 3HCl + H3BO3) and alkaline digestion (0·5 m NaOH). It is suggested that allophane originates from the reaction of acid solutions released during the weathering of sulphides with acid volcanoclastic rocks. Silica-alumina gels were deposited in holes formed during earlier dissolution of the dolomite associated with the barite ores. Later processes of desilication partially transform allophane to gibbsite.

Solutions obtained from soils in the Galicia Region of NW Spain had considerably lower activities of Al3+ when obtained by a speciation procedure (fractionation with an ionic column and application of specific software) than when obtained from concentrations of reactive Al (colorimetry with pyrocatechol violet) by a calculation that only considers simple hydroxylated species. Using the speciation method, many of the solutions obtained from surface horizons are unsaturated for most minerals, especially in granitic areas.

Two samples of illite-smectite (I-S) isolated from Upper Jurassic clays in well 2/7-3 (3365 m) and well 2/11-1 (4548 m) have been investigated by scanning tunnelling microscopy (STM), and the particle shape and dimensions have been correlated to results from transmission electron microscopy (TEM) on shadowed specimens and results from atomic-force microscopy (AFM). By STM, lath-like and equant particles were observed in both samples, some of the particles having sharp edges. In the I-S from well 2/11-1, spiral-shaped particles were also seen. For both samples, the most frequent particle diameter was 100–200 Å. Particle-thickness distributions from STM and TEM were similar for the I-S from well 2/7-3, being dominated by 10 Å thick particles. For I-S from 2/11-1, the STM particle-thickness distribution has a predominance of 20 Å thick particles, but the TEM particle-thickness distribution is broad, with about equal amounts of 20, 30, 40, 50 and 60 Å thick particles. The AFM particle-thickness distribution for this I-S resembles the TEM thickness distribution. It is concluded that mainly thin (10 and 20 Å) particles are seen by STM. Failure of AFM to show sharp particle edges (seen in STM and TEM) might be attributed to the AFM tip movement or tip shape. In STM, I-S particles from well 2/7-3 have peaks along edges, whereas I-S particles from well 2/11-1 have rims. These rims are also seen in AFM and are therefore real geometrical features, probably a result of two-dimensional growth, whereas the spirals in the I-S from well 2/11-1 demonstrate three-dimensional growth. The minimum thickness of most particles is 10 Å.

The charge transfer process that occurs in two samples of Wyoming montmorillonite of different grain size pillared with Zr by interaction with perylene (Pe) and tetracyanoethylene (TCNE) has been studied. These smectites are strongly affected by the exchange of Zr and appear to be strong electron acceptors and weak donors. The ESR results show that their ability to form charge transfer radicals is related to the details of preparation, which most probably control the accessibility of Pe and TCNE to the internal surface.

Sodium smectite clay, commercially available in the form of bentonite powder, serves as a very effective water flow barrier and cation exchanger. At bulk densities between 1·9 and 2·2 g/cm3 after water uptake to reach complete saturation, the hydraulic conductivity is of the order of 10−14 to 10−13 m/s. The swelling potential produces a tight contact with confining structures, which makes bentonite ideal as overpack of rock-deposited radioactive canisters and for borehole and shaft sealing. At bulk densities between 1·1 and 1·3 g/cm3, the hydraulic conductivity of smectite gels is still sufficiently low to make them useful as effective grouts for sealing rock fractures. The longevity in a granite environment is very significant and the ultimate transformation residue—hydrous mica (“illite”)—preserves some of the excellent sealing properties of smectites.

Adsorption of Cs on two samples of marl with different calcite, quartz and clay contents and surface areas of ∼10 m2/g was followed using the batch sorption technique. The experiments were carried out in an atmosphere of N2/1% CO2 using a synthetic groundwater of pH 7·3 and an ionic strength of 0·1 m. The initial Cs concentration ranged from 10−8 to 10−4m. Sorption of Cs was non-linear, fast and reversible. At equilibrium Cs concentrations <10−8m, an isotope exchange mechanism appeared to operate, whereas at higher concentrations, sorption involved ion exchange. The distribution coefficients ranged from 23–995 ml/g. They varied markedly with rock/water ratio; this variation could be explained in terms of the non-linear isotherm displayed by Cs. Although the two samples of marl differed in composition, uptake of Cs on both samples was very similar because the content of the principal sorbing component (illite) was the same in both samples.

The term ferrihydrite, originally defined as a poorly ordered hydrous ferric oxide exhibiting five or more distinctive X-ray diffraction maxima, has come to be extended to include species that exhibit only 4, 3 or 2 of these maxima. It is pointed out here that hisingerites may exhibit a similar 2-line diffraction pattern. The laboratory synthesis of hisingerites show that they can form under soil conditions. Acid oxalate buffer of pH 3, a reagent considered a fairly specific solvent for ferrihydrite, extracts the iron content of these synthetic hisingerites quantitatively.