Cambrian and Ordovician pelites and greywakes from the Iberian Range were studied using XRD, EMPA and AEM/TEM techniques, lllite and chlorite are the main phases in Cambrian <2 µm fractions. Illites show crystallinities (IC) from 0.28 to 0.23°2θ the 2M1 is almost the only polytype; they do not have expandable layers, and they are heterogeneous in composition. Chlorites show two compositional types, both containing variable proportions of smectite-like layers. Clinochtores growing over bedding surfaces are also present. An evolutionary trend from anchizone to near the anchizone-epizone limit has been proposed for Cambrian samples.

In the Ordovician <2 µm fractions, illites are associated with minor chlorites and kaolinites. The ICs range from 0.68-0.28°2θ the 2M1 polytype dominates over 1M, and it is associated with illitesmectite mixed-layering (R3 ordering). An evolutionary trend from diagenesis to low grade anchizone has been inferred.

Chemical analyses of coarser detrital micas indicate muscovite and phengite compositions. The compositional heterogeneity exhibited by authigenic and detrital phases suggests that chemical equilibrium was not attained.

Kaolinite-ferrihydrite and montmorillonite-ferrihydrite associations were prepared following a procedure based on the Russell method for the synthesis of ferrihydrite and the texture of the clay-ferrihydrite complexes was studied using different techniques. The textural properties of kaolinite were little affected by the Fe association, showing only a slight increase in the specific surface area measured by nitrogen adsorption and a decrease in the largest pores (>10 µm), as measured by mercury porosimetry. In contrast, the nitrogen specific surface area of the montmorillonite complexes was much higher than that of the clay without Fe and the pore structure depended on the amounts of Fe in the complexes. Application of the fractal approach to nitrogen adsorption data indicated that the surface roughness (microporosity) was greater for the complexes prepared from diluted Fe(III) solutions, in agreement with the information obtained from classical interpretation of the adsorption isotherms (shape of the isotherms and t-plots).

In the course of hydrothermal experiments with a saponitic clay, evidence for the dissolution of the accessory sepiolite and the formation of smectite has been detected above 120°C Hydrothermal reactions with a clay to water ratio of 1:3 were performed at temperatures of 60, 90, 120, 175 and 200°C with time intervals of one month to one year.

The BET surface area and cation exchange capacity (CEC) are correlated with the sepiolite and the smectite content determined from XRD data. These relations have been used to recalculate the time dependence of the mineral contents in the time/temperature conditions of the experiments. The Ea values obtained for sepiolite dissolution (7-18 kcal/mol) or smectite formation (4.8-5 kcal/mol) indicate that sepiolite dissolution controls the rate of the process. Both results fit an apparent firstorder reaction and the system seems to evolve to a stable mineral composition in a short time period, ranging from one to 10 years as temperature decreases.

From mineralogical and chemical characterization of two waste-rock piles from Vigonzano and Libiola sulphide mines in the northern Apennines, two types of fine-grained weathering products were recognized, One, from the Vigonzano mine, has a typical blue colour and consists of the Cu-Al sulphate of the woodwardite group. Its formation is related to an alkaline geochemical barrier, it is rather stable in acidic solution, and it controls Cu and Zn dispersion in the surrounding environment. The other group of sediments has a typical ochreous colour. Vigonzano samples consist mostly of goethite, whereas ferrihydrite is abundant in the Libiola sample. The ochreous sediments are enriched in Co, As, Mo, Se and Mn, thus significantly reducing the potential environmental hazard of the site, whereas solubility tests indicated possible problems due to AI dissolution at Libiola.

The grain size of raw materials influences their behaviour during the technological process and affects many properties of building clay products. Over the last few years, brickworks have been technologically updated and grain size requirements have been modified to ensure good behaviour during shaping and drying. Therefore, the reference schemes used to assess the suitability of clays, such as the classic Winkler diagram, should be updated.

For this purpose, the grain-size distribution of 350 clays currently used in ~240 Italian plants was determined by X-ray monitoring of gravity sedimentation. Raw materials are basically represented by silty clays and clayey silts, while bodies present a narrower grain-size range. With reference to the Winkler diagram, most of the Italian bodies fall within the field of ‘thin-walled hollow bricks’, with no significant differentiation among the various product types.

In order to improve the grain-size characterization of bodies, a new classification scheme for Italian raw materials is proposed, based on three ranges: >10 µm, 2-10 µm and <2 µm, respectively. It allows distinction of specific grain-size features of bodies for (a) facing bricks; (b) roofing tiles; and (c) lightweight blocks, paving bricks and hollow slabs.

Carbonate-bearing ceramic bodies are frequently used in the manufacture of bricks, roofing tiles, wall and floor tiles, pottery and tableware. During the firing of these bodies, clinopyroxene is usually formed in very small crystals, 1-5 µm in diameter or less. In the literature this phase is generally referred to as diopside, but no quantitative data are available. In order to chemically characterize these ‘ceramic’ pyroxenes, nine industrial products were analysed by XRF and XRD (bulk sample) and SEM-EDS (fracture surface). Quantitative ZAF analyses of pyroxene crystals showed a certain chemical variability: SiO2 35-50%, Al2O3 9-20%, Fe2O3 1-15%, MgO 3-14%, and CaO 16-25%. Sodium, K and Ti are always <1%, while ferrous iron is always <0.2% in the bulk sample. Overall, ‘ceramic’ clinopyroxenes present wide chemical analogies with ‘fassaite’, e.g. the abundance of aluminium and ferric iron, and the excess ofwollastonite molecules with respect to the diopside-hedenbergite series.

An attempt has been made to assess new potential applications for the Bailén clays, traditionally used for manufacturing bricks, based on mineralogical, chemical, particle size, plasticity and firing results. Raw materials and mixtures used by the local factory were selected and tested with the addition of some diatomite, feldspar or kaolin. Based on their properties, clay materials from Bailén might be suitable for making porous red wall tiles, clinker, vitrified red floor tiles and porous light-coloured wall tiles by pressing; the first could be manufactured from the raw materials and mixtures currently used by the local manufactures. On the other hand, stoneware shaped by extrusion, such as perforated bricks, facing bricks and roofing tiles, can be also manufactured from the mixtures used at the factory if they contain 20-25% carbonate and small amounts of iron oxides; lightweight bricks require black and yellow clays with diatomite.

The interaction between phenyl salicylate and sepiolite has been studied using drugclay systems obtained by melting and grinding. The samples have been characterized by powder Xray diffraction, differential thermal and thermogravimetric analyses, and Vis-UV and FT-IR spectroscopies. ‘Free’ water molecules are steadily substituted by the drug molecules, without any chemical change as shown by FT-IR. The systems prepared improved the protecting ability of the pure sepiolite or the pure drug against ultraviolet radiation, especially in the so-called ‘C’ range (290-190 nm).

A dioctahedral bentonite was treated hydrothermally with KCI solutions (0.025-1 M) at different temperatures (60-200°C) and times (1-360 days) to evaluate its use as a barrier for radioactive waste disposal. Equations relating adsorbed K on smectite with initial and equilibrium K concentrations in solution, temperature and time have been obtained. These equations are useful for modelling the influence and behaviour of these variables and contribute to the performance assessment calculations for radioactive waste repositories. Likewise, the thermodynamic parameters of the K adsorption process have been calculated. Other relationships, including silica in solution and pH, are also shown.

The clay mineral associations in the Cretaceous-Tertiary Boundary (KTB) and in the Danian and Maastrichtian levels of sections from the Mediterranean and the Atlantic Domains have been studied. The Mediterranean sections have a single mineral association consisting of smectiteiltite and kaolinite, whereas the Atlantic sections have several associations: illite-chlorite, illite-R1 I-S-kaolinite and illite-R 1 I-S-chlorite. Data are presented relating to the influence of K-feldspars and Fe oxide sphemles on the clay mineral associations. Study of rare-earth elements shows that regional geological factors affect the clay mineralogy of the KTB, examples showing significant anthigenesis in the Mediterranean sections, and important detrital supply in all the Atlantic sections. We propose that the KTB studied in these marine sections is equivalent to the uppermost layer of the two-layered clay unit originating in a cloud of a vapourized bolide. Regional tectonic conditions have been responsible for differences in clay sedimentation in these geological domains and among the stratigraphic sections of the Atlantic Domain.

A mineralogical and microstructural study of bentonites from 'Cerro del Aguila' located in the Tagus Basin (Toledo, Spain) was carried out using XRD, SEM and TEM observations and chemical data obtained by TEM-EDX. The bentonites are mainly composed of trioctahedral smectite with a unit-cell formula (Si3.76Al0.24)(Al0.44Fe3+0.26Mg1.81)Ca0.05K0.19O10(OH)2 and small amounts of illite. The relationships between illite and smectite particles observed by SEM and TEM allowed the study of the weathering process of illite to form smectite through possible intermediate stages. The transformation begins as an exfoliation normal to the stacking direction and develops by opening of the interlayer spacing, the replacement of K+ by hydrated interlayer cations and slight reorganization of the 2:1 layer structure. The so-called solid-state transformation process then proceeds by further dissolution and the formation of a colloidal phase acting as raw material in the growth of new phyllosilicates such as smectite.

The nature and mineralogy of mixed Al and Fe(III) gels (initial Fe/Al molar ratios (Ri) of 1.0 and 2.5) formed at pH values ranging from 4.0 to 10.0, both in the presence and absence of citric acid (citrate/Fe + AI molar ratio (Rcit) of 0.01 and 0.1) and aged for a long period at room temperature and at 50°C have been studied. The complexes showed considerable differences in the mineralogy of the precipitation products. The samples formed at Ri = 1.0 contained ferrihydrite at pH 4.0, ferrihydrite + gibbsite at pH 5.0-7.0, and hematite + Al(OH)3 polymorphs + ferrihydrite at pH 9.0-10.0. The samples formed at Ri = 2.5 had greater quantities of poorly crystallized ferrihydrite. Large amounts of Fe+Al (25-82%) were solubilized from the samples aged for 60 days at 50°C by ammonium oxalate. The addition of increasing concentrations of citrate to the gel suspensions containing equimolar amounts of Fe and AI strongly inhibited the formation of Al(OH)3 polymorphs both at pH 5.0 or 8.5 by promoting the formation of short-range ordered materials. Citrate added initially to Fe-Al solutions (R*cit = 0.1) completely inhibited formation of crystals even after 135 days at 50°C.