This study aims to find alternatives to some overexploited deposits in the north of Tunisia. The clays of the Sidi Khalif formation, of Uppermost Jurassic to Lower Cretaceous age, seem suitable to support this strategy, due to their abundance. In terms of mineralogy, they can be divided into two distinct groups, related to their palaeogeographic and eustatic contexts. The clays of the Sidi Khalif formation from Jebel Houareb (JH) and Jebel Meloussi (JM) are richer in clay minerals, while those of Jebel Rhouis (JR) and Jebel Boudinar (JB) zones are dolomite-rich. The compositional differences between the two groups influenced their technological behaviour in production of ceramic tiles. Upon firing, forsterite and gehlenite crystallized in the carbonate-rich JR and JB clays, whereas mullite formed in the JH and JM clays. Concerning their ceramic properties, the tiles made from JR or JB clays showed low bending strength and high water absorption. For JH and JM, the tiles had slightly greater mechanical resistance, but exhibited considerable linear shrinkage. These defects were partially corrected by introducing new formulations based on the same clays and by altering the firing cycles (HM1, HM2, RB1 and RB2). With these modifications, “Porcelanico” and “Monoporosa” technologically conforming tiles were obtained from HM2 and RB2 formulations, respectively.

Smectites of sedimentary series from a playa lake system from Calatayud Basin have been studied by XRD and TEM chemical microanalyses. Clay particle microanalyses show complete continuity between dioctahedral aluminous and trioctahedral magnesian smectites. Aluminous smectites have been classified as montmorillonites and ferribeidellites, both with compositional variability. They represent detrital phases resulting from weathering in the source area. Compositionally-intermediate smectites (beidellite-saponite and montmorillonite-stevensite) seem to correspond to weighted mean compositions of di- and trioctahedral phases stacked together in the same particle. They represent intermediate transitional stages from detrital to authigenic smectites in more distal basin facies. Trioctahedral smectites, although called saponites and stevensites, are actually random mixed-layer kerolite-Mg-smectite with a high percentage of expandable layers. They represent authigenic clays formed from solutions with high pH and Mg content as a result of evaporative concentration. The variability in composition of smectites, both within the same sample and amongst different samples, is a possible consequence of the heterogeneity in the local chemical environment, and so, equilibrium may be only reached locally in a large variety of microsystems.

The results of a new technique for the measurement of the thickness distribution of fundamental particles are reported. The technique is based on high-resolution transmission electron microscopy (HRTEM) of Na-saturated mixed-layer illite-smectite dispersed in polyvinylpyrrolidone (PVP-10). Intercalation of PVP-10 increases the spacing of expandable interlayers and changes the arrangement of particles so that the number of layers per fundamental particle can be counted easily on HRTEM images. The data obtained by HRTEM on PVP-10-intercalated illite-smectite of hydrothermal origin are compared with data from the Pt-shadowing technique. A good agreement between the two methods for the measured thickness distributions, mean thickness and expandability confirms the reliability of the new technique. The same technique is applied to a set of four sedimentary samples with different expandabilities (83-18%). The thickness of illite particles from shales and claystones has a lognormal distribution. Detrital anddiscrete illite particles can be distinguished from the thickness distribution of authigenic illite.

The spatial and vertical distributions of six clay mineral assemblages were identified in the pelagic marls and marly limestones and in the Ammonitico Rosso of the Lower Jurassic in the Betic Cordilleras (SE Spain). The six assemblages contain varying proportions of illite, kaolinite, chlorite, smectite and mixed-layer illite-smectite. The clay mineralogy and the geochemical data, particularly for the rare earth elements, indicate that the sediments were deposited in a pelagic environment influenced by a nearby continent. The source areas were many and lithologically varied. Clay mineralogy and geochemistry are shown to be most useful in the reconstruction of the palaeogeography of a basin in a passive continental margin.

The Fe oxide mineralogy behind the reddish colour (up to Munsell 10R) of a soil and four Quaternary surface deposits from central Jutland (Denmark) was investigated by XRD, TEM, Mo¨ssbauer spectroscopy and bulk saturation magnetization. The red soil (Naesset) consists of a 1 m deep patch, ∼10 m2 in area. It is one of at least 5 –10 isolated spots of limited size which contain hematite and maghemite, and are probably due to local fire.

The four more extended (several hundred m2) red sediments (Salten Skov, Salten, Pot Molle and Laasby) all occur at the feet of slopes and formed from Fe2+-containing seepage water. They contain 25 – ∼100% Fe oxides, originally consisting of ferrihydrite. The well-drained parts of the deposits are at present all dominated by goethite. Hematite and maghemite were also identified at two sites in the top ∼25 cm, one site containing goethite and hematite and probably a little maghemite, and the other goethite and probably hematite. The presence of hematite and particularly maghemite in the surface sediments could be explained by heating of goethite. However, there is no historic or prehistoric evidence of heating activity, and the spatial extension is much wider than that of normal human events. In contrast to the burned soil site, goethite is still present in the upper layers together with a high content of organic matter. Thus, although the present belief is that the deposits formed by heating, site evidence is to the contrary.

Authigenic chlorites occurring as pore linings in reservoir sandstones have been investigated by XRD and TEM/EDAX. Both methods identified the Ib (β = 90°) polytype. TEM/EDAX analyses suggest that the chlorites are Al-rich, Mg-chamosites with Fe/(Fe + Mg) > 0·47. Octahedral Al exceeds tetrahedral Al, resulting in octahedral totals of less than the theoretical 12·0. Compositions were estimated from XRD data using the equations after Brindley (1961) and Shirozu (1958). XRD-determined compositions are relatively enriched in tetrahedral Al and octahedral Mg, giving Fe/(Fe + Mg) > 0·4 and suggesting that the chlorites are Al-rich clinochlores. XRD estimates plot in the same compositional area as authigenic Ib (β = 90°) chlorites of Hayes (1970), but also within the compositional area of metamorphic chlorites. Caution should be exercised when estimating the composition of sedimentary chlorites by XRD as results appear to overestimate Mg content because of the excess of octahedral R3+ over tetrahedral R3+.

Mossbauer spectroscopy was used to study the valence and bonding changes of iron in (a) lattice sites, and (b) cation exchange sites during thermal treatment of kaolinite and halloysite. Lattice iron which is initially in octahedral sites occurs in octahedral and tetrahedral sites at the completion of the thermal reactions. At temperatures below 650°C some divalent ions in cation exchange positions become trivalent and assume octahedral co-ordination, which they retain until the later stages of mullite formation. The implications of the work on the high temperature reaction mechanism and structural sequence are discussed.

Mineralogical and chemical examination of Tertiary interbasaltic clays from the Faeroe Islands revealed three types of alteration of volcanic tufts and basalts: (1) Argillization of volcanic tuffs within a lacustrine environment resulted in the formation of aluminous beidellites and metahalloysites; these clays are associated with extensive coal layers at Suduroy. (2) Argillization of volcanic tuffs due to hydrothermal action resulted in the formation of thick layers of ferriferous beidellites associated with small amounts of hematite and zeolite (e.g. at Nolsoy). (3) Meteoric alteration of volcanic tufts and basalts, which took place under hot climatic conditions and contrasting seasons, led to the development of ferriferous and aluminous-ferriferous beidellites, metahalloysite, kaolinite, hematite and goethite in low (Høv profile) or high (Øravik profile) topographical positions. The three processes occurred individually or were superimposed.

Structural formulae and other crystallochemical parameters were used to study different species of dioctahedral micas in clay and coarse gravel fractions of horizons from a red soil (Ultic Haploxeralf) in southern Spain. Mineralogical analyses using X-ray powder diffraction, and measurements of the b0 parameter revealed dioctahedral micas, illite and paragonite. Structural formulae established from electron microprobe analysis and energy dispersive X-ray analysis showed the illites to be K mica related in elemental composition and structure to muscovite and phengite. The paragonites were found to be closer to ideal mica. Structural formulae for Na-K dioctahedral micas were obtained with crystallochemical characteristics intermediate between those of Na micas and K micas. The possibilty of these micas representing individual mineral phases or intergrowths of Na and K micas is discussed. In the soil profile, micas from the Bt horizon showed the largest crystallochemical changes induced by pedogenesis.

Samples of muscovite and phlogopite of particle sizes varying from less than 5 µm to 500 µm were allowed to stand in distilled water and in several NaNO3 solutions. The modifications of their surface were determined by thermovolumetric measurements of the extra-water associated with the altered rim.

Phlogopite undergoes congruent dissolution due to protonic action at low pH and vermiculitization by sodium under other conditions. Muscovite ground and aged in water suffers potassium hydrolysis and silica dissolution both of which contribute to the accumulation of aluminium on the surface. The altered rim, which develops on basal surfaces as well as on the edges, has an extra-water content of about 1·2 H2O molecules per accumulated Al atom; the surface can be cleaned by a treatment at low pH.

During the installation of the buffer in a deposition hole of an HLW repository, it is necessary to control water flow from the fractured rock into the deposition hole. Water flow with inflow rate greater than 0.001 l/min may cause piping and erosion of the buffer, and may trigger mass redistribution of the buffer, sedimentation and material separation of bentonite materials. This paper describes the condition of parameters which cause piping and erosion; revised conditions which keep advection, inflow rate, buffer component, gap between buffer materials, gap between outside wall and buffer block, and type of water. The results from the experiment show the condition of the self-sealing function of bentonite materials, formation of piping, allowable limit of inflow rate in the case of an Na type bentonite block of 70 wt.% Kunigel V1 and 30 wt.% silica sand, or a pellet of 100 wt.% Kunigel V1. Piping and erosion continue until the engineered barrier (EB) is filled with water, and then the hydraulic gradient becomes small. Piping may lead to erosion and redistribution of material which needs to be taken into account in the long-term performance assessment.

The clay mineral assemblages of the Tithonian and Berriasian sediments (Tera and Oncala Groups) in the eastern part of the Cameros basin are investigated at seven localities. The lowest-grade assemblage, located on the southern border of the basin, contains calcite + quartz + hematite + kaolinite + mixed-layer illite-smectite (R = 1, 65 85% illite layers) + discrete illite (IC = 0.5 0.65Δ°2θ). Systematic increases in the illite and chlorite crystallinities suggest increasing metamorphic grade from the northwest part of the basin to the southeast. This trend does not follow the pattern previously described for the overlying late Berriasian–early Aptian sediments (Urbión and Enciso Groups), which exhibit a higher metamorphic grade. This may result from local variations in sedimentary facies, as well as the circulation of hot migratory fluids. Tertiary compression occurring long after the main metamorphic event is considered to be responsible for the enhanced illite and chlorite crystallinities measured in the SE extreme of the basin.

Calculations previously used to distinguish between methanol adsorbed in micropores between clay microcrystals (external) and that present in the interlamellar space (internal) of variable charge Ca-montmorillonites have been extended to homoionic Li-, Na- and Bamontmorillonites. It is shown that both the shape and the magnitude of the internal isotherms are in good agreement with X-ray diffraction data. Furthermore, the apparent molecular packing of methanol in the interlamellar space is related specifically to the nature of the charge balancing cation.

This work deals with the formation of humic-like compounds, products of the Maillard reaction between glycine and D-glucose, on clay (K+, Ca2+ and Al3+-saturated montmorillonite and kaolinite) and quartz systems in the presence of the same cations. Natural quartz was used as the control while the effect of cation type, mineral substrate and CEC was evaluated. All the systems form humic-like substances that are probably responsible for the decrease in the pH (H2O) after 30 d. The type of cation does not influence the overall production of humic substances, while the amount of cations controls the formation of humic-like material especially in the presence of clays. A mineral surface is necessary to synthesize molecules with this high degree of complexity.

Fulvic-like compounds are produced in great amounts on natural quartz and their formation is hampered by the presence of ‘free’ cations, regardless of their amount. Humic substances do not penetrate the interlayer of montmorillonite.

Clay mineral and trace element data indicate that sediments in the vicinity of the North Mid-Atlantic Ridge derive from material of both Icelandic and Canadian origin. These sources agree with the marine and atmospheric circulation patterns observed in this area.

Sorption of molecular amines by montmorillonite involves protonation of the amine group and hydrolysis of the interlayer cation. Sorption and subsequent desorption of amines may render some of the interlayer cations non-exchangeable, thus causing partial 'chloritization' of the montmorillonite. The effect is stronger with interlayer Al than Ca ions and depends upon the amine sorbed.

Weathering products of a serpentinized Iherzolite were investigated using optical microscopy, X-ray diffraction, infrared spectroscopy, and electron microprobe and wet-chemical analysis methods. The original mineral assemblage of the rock was chrysotile-enstatite-diopside-picotite-magnetite-calcite. Rock porosity governed the types of chemical microsystems from which the clay minerals were derived. These microsystems were grouped into three types. (1) Grain microcracks and grain boundaries. These were the earliest manifestations of weathering. Only pyroxenes were affected and transformed into talc + iron oxides. (2) Plasma zones in which the rock structure was preserved. The talc + oxide and chrysotile were both altered into a saponitic mineral. Picotite was oxidized to oxipicotite. (3) Fissure zones. In the argillized zones the rock was restructured. Saponite was altered to nontronite + magnesium silicate gel. Talc was also transformed to the same gel. Fissures were often filled with clay cutans and some were edged with iron oxides. Mineral facies in the different zones have been plotted in Si-R2-R3 coordinates.

Although investigation of the hydraulic conductivity behaviour of zeolite-bentonite mixtures (ZBMs) has been a topic of interest for researchers recently, the influence of compaction water content on the hydraulic conductivity of ZBMs has not been studied so far. This study discusses the hydraulic conductivities of ZBMs and compares the results with those of sand-bentonite mixtures (SBMs). The hydraulic conductivities of SBMs were unaffected by compaction water content and bentonite content, but the hydraulic conductivities of ZBMs were substantially different in mixtures containing 10% and 20% bentonite. The hydraulic conductivity of 10% ZBM (i.e. containing 10% bentonite and 90% wt. zeolite) gradually decreased as the water content increased to optimum water content and then it tended to decrease rapidly when the water content exceeded the optimum. In contrast, the hydraulic conductivity of 20% ZBM sharply decreased at the early stages of compaction water content (i.e. on the dry side of optimum water content) and levelled off when the water content was at the optimum water content. However, there is at least one order of magnitude difference between the hydraulic conductivities of ZBMs and SBMs, supporting the zeolite network model as suggested in previous works.