A set of Silurian black shales from Sierra de Albarracín (NE Spain) corresponding to two different sections was studied to determine the relative influence of diagenesis, igneous activity, and regional tectonics on the clay-mineral genesis. The coexistence of pyrophyllite, I-S interstratifications (R1), ammonium-rich illite, potassium illite, kaolin, and chlorite is not the result of prograde evolution during diagenesis – very low-grade metamorphism. Three different stages may be inferred: (1) sedimentation of black shales (Aeronian, Lower Silurian, to basal Ludfordian, Upper Silurian) and the subsequent diagenetic process producing the coexistence of quartz, illite, kaolinite, organic matter, etc.; (2) intrusion of andesitic sills producing hydrothermal alteration and crystallization of pyrophyllite, ammonium-rich illites, smectite, I-S R1 phases and jarosite; and (3) and folding of shales and sills and development of penetrative schistosity during the late Variscan leading to illite and paragonite recrystallization reaching the anchizone grade.

The saponite examined occurs as two 0.1 m thick layers in a Pliocene sequence consisting of dolomite and dolomitic marl. To characterize this material, mineralogical and structural analyses (XRD, SEM and FTIR), thermal analyses (DTA, TG) and chemical analyses (ICP-ES) were performed. From XRD patterns of randomly-oriented powder samples, the first basal reflection appears as an asymmetric and broad peak with d001 values varying between 16.55 and 17.32 Å. In oriented and air-dried samples, this reflection occurs between 14.45 and 16.42 Å and is fairly symmetrical with FWHM of 2.7º2θ. Oriented and ethylene glycol-solvated samples produce a rational series of basal reflections, where 001 occurs at ~17.8 Å as an intense, narrow (1.1º2θ) and fairly symmetrical reflection. Upon solvation with glycerol, the 001 reflection shifts to ~18.7 Å.

The chemical composition of this saponite is similar to stevensite. However, the structural formula of Na0.114Ca0.013K0.003(Mg2.957Al0.004Fe0.028Ti0.004)(Si3.826Al0.174)O10(OH)2 indicates that vacancies in the octahedral sheet do not exist. The negative layer charge arises nearly entirely from the substitutions in the tetrahedral sheet, with the net layer charge of –0.148, smaller than for common smectites.

Due to the XRD characteristics and particularly the layer-charge distribution, it was concluded that this mineral is a Mg-rich saponite with low layer charge. The saponite was formed by direct precipitation in an alkaline lake environment from Mg- and Si-rich solutions at high pH.

In the last twenty years a number of workers have turned their attention to a study of the grinding of clay in an attempt to elucidate a mechanism of the process and the nature of the resultant products.

The pioneers in this field were Kelley et al. who investigated the grinding of bentonite in 1931 and the grinding of kaolinite in 1936. In the earlier results the product showed a slight fogging of X-ray lines and in the latter an increased loss of water when it was examined by controlled dehydration at elevated temperatures; in both systems an increase in base exchange capacity (B.E.C.) was observed. The authors suggested a purely physical disintegration theory, i.e. that decreased particle size could account for all the observations; they postulated fracture both parallel and perpendicular to the cleavage plane and this was supported by the electron microscopic investigations of Shaw (1942).

The aspect ratios of common clay minerals have been determined from conductometric titrations. The sample set comprises 11 Na-saturated bentonites, 16 smectites with different interlayer cations, three illites/muscovites and two talc dominated specimens. It is shown that the aspect ratios of smectites saturated with divalent cations are lower than those of the same smectite saturated with a monovalent cation. This observation is discussed in terms of the number of smectite layers making up a particle.

The physical properties of three montmorillonites before and after heating were studied by reflectance colorimetry, X-ray diffraction (XRD) and infrared (IR) and Mössbauer spectroscopies. Colorimetric data, though not directly relatable to sample mineralogy, provide cheap and rapid information on the temperatures of sample breakdown. X-ray diffraction provides information on sample mineralogy and the transformations that develop during firing and allows the major phases formed in the course of firing to be identified, whereas IR data provide information on water and hydroxyl loss and the final breakdown of the montmorillonite structure. Mössbauer spectroscopy gives information on Fe2+ oxidation (where applicable) and reveals subtle variations in Fe site coordination and Fe mineralogy, including the formation of Fe oxides – that can be quantified in proportions as low as 0.1% – following structural breakdown of the montmorillonites.

The <2 µm clay fractions from low-grade metabasalts of eastern North Greenland are mixtures of mafic phyllosilicates and celadonite that show complex X-ray diffraction (XRD) patterns. Interpretation of such patterns is difficult and subjective using only visual examination of peak positions and shapes. Deconvolution analysis offers a less subjective means of identifying peak positions for overlapping peaks and is applied to several composite peaks in a pattern; the peaks identified are then rationalized in terms of specific mixed-layer phases. Comparison against NEWMOD patterns of the identified clay mixture provides an additional constraint on the phases identified. Three mafic phyllosilicates, discrete chlorite and two chlorite-smectites with 60:40 and 80:20 proportions are demonstrated in the same XRD pattern. Modelling using NEWMOD of a mechanical mixture between these mineral shows an excellent match to the observed XRD pattern. The recognition in low-grade metabasalts of chlorite and random and different varieties of regular mixed-layer chlorite-smectite offers support for the classical model of a tri-smectite to chlorite transition. This is in contrast to an alternative model proposing smectite and chlorite end-members with corrensite as a discrete phase crystallizing directly without intervening mixed-layer chlorite-smectite.

Kaolin wastes from the Capim and Jari regions (Brazil) were used to produce sodalite under the same conditions used in the Bayer process, in order to control its formation when necessary. Of the two kaolin source materials, the kaolinite from the Jari region was more reactive in the synthesis of sodalite, which is attributed to the low degree of structural order of this clay mineral which increased its reactivity. At a temperature of 150°C and with a Na/Al ratio of 2, although the kaolinite did not react completely, sodalitewas the primary reaction product. An increase in the temperature to 200°C provoked the complete reaction of the kaolinite only for the products in which carbonate and sulfate were used. With a Na/Al ratio >2 and for both of the temperatures, the kaolinite reacted completely to form sodalite.

The interlayer structures in one- and two-layer hydrates of Na-vermiculite are described by presenting the positional parameters of their constituent atoms, including protons.

The revision of these structures has been accomplished by: (1) determining accurate water contents of the two hydrates by thermoanalysis (TG, DSC); (2) using earlier X-ray diffraction data published by Slade et al.(1985) and de la Calle et al. (1984) as a reference; and (3) applying least-squares refinements when considering the constraints for atomic distances and bond angles between interlayer constituents.

In the 1.485 nm hydrate of Na-vermiculite (nH2O/nNa ≈ 4), sharing edges of Na(OH2)6 octahedra cause their chainlike arrangement. The chains are aligned along [100] and are stabilized by H-bonds between interlayer water molecules and oxygens of the silicate layer. The partial loss of these bonds during dehydration forces the stacking order to change from V3 to Vc in the resulting 1.185 nm (nH2O/nNa ≈ 2) hydrate.

This new understanding may help to explain differences in the rotational correlation time of water molecules between one- and two-layer hydrates of vermiculite as observed by quasielastic neutron scattering (Swenson et al., 2000).

Clay mineral evolution in diagenetic and very low-grade metamorphic sedimentary rocks from the Maláguide Complex was studied using the following parameters: illite and chlorite crystallinity, b cell dimension of illite, chemistry of chlorite, and the occurrence and distribution of the following phyllosilicates: I-S mixed-layer minerals, kaolin polytypes, chlorite-bearing mixedlayer minerals (tosudite and mica-chlorite interstratifications), vermiculite-like minerals, paragonite and biotite. The distribution of IC values permits the subdivision of the study area into three zones: diagenetic, anchizone and epizone. On the contrary, the distribution of CC values cannot be used in the study of the metamorphic zonation. The mineralogy and b dimension of illite indicate that the Maláguide samples display a low to low-medium pressure metamorphism, also characterized by steep temperature gradients.

The correlation between IC data and distribution of other significant minerals has permitted the establishment of a zonation within the chlorite zone, which is confirmed by the appearance of some index minerals, such as paragonite, biotite, chloritoid and andalusite.

The infrared spectrum of water adsorbed on K-hectorite has been studied in the frequency range 2600–4000 cm−1 on samples equilibrated with relative humidities of 0% to 100%. The model proposed by J. Mamy for the molecular array of water upon the mineral surface has been used as a starting assumption. A ‘unit cell’ made of two H2O molecules is then considered as a possible theoretical basis for the interpretation of the infrared spectrum. When taking into account this unit cell six stretching frequencies may be anticipated. The six components of the OH stretching band are clearly resolved at −95°C at room temperature a Curve Resolver was used to analyse the composite band, which was recorded at various incident angles (0–45°). From the variation of the integrated absorption of each component band given by the curve resolver, the orientation of the dipolar moment is calculated, and compared with the theoretical one deduced from the model.

A single measurement of the adsorption of atmospheric air on a dried, finely-divided solid at − 183°C carried out in a simple apparatus which does not require a high vacuum system, can be related empirically to the specific surface as determined by the Brunauer, Emmett and Teller procedure, with, generally, less than 10 per cent. error. The method is rapid and simple, and therefore suitable for routine use.

Redox activation (reduction of structural Fe) of smectites greatly alters their chemical reactivity and physical properties, which may be exploited for various environmental, agricultural or industrial purposes. Their re-oxidation during preparation, characterization, and use is, however, a significant risk to their utility. In this study, methods and apparatus were developed and described which mitigated reoxidation. Ferruginous smectite (sample SWa-1, Na saturated) was used as the model smectite. It was reduced with sodium dithionite in a citrate-bicarbonate buffer solution at 70°C for 4 h, which achieved a maximum Fe(II)/total Fe ratio of 0.9113 ± 0.0048. The first step in rendering reduced samples useful is to remove from them the reducing agents and other solutes present during reduction. This was accomplished in the present study by reducing the sample in an inert-atmosphere reaction tube (IRT) (a 50 mL centrifuge tube equipped with a removable septum cap), then removing solutes from the suspension by centrifuge washing. The washing steps were performed with the aid of a controlled-atmosphere liquid exchanger (CALE) which provided connections between the sample suspension and deoxygenated solutions. The reduced state was measured by 1, 10-phenanthroline or by Mössbauer spectroscopy at 77 K to give Fe(II)/total Fe ratios. Some samples were freeze dried after washing. Results revealed that if reduced smectites are washed without protection from atmospheric O2, the extent of reoxidation is on the order of 40 to 60%. If the sample is subsequently dried, reoxidation increases to more than 76%. If the sample is protected using the IRT and the CALE, however, reoxidation is decreased to less than 2%. Freeze drying in a glove box allowed reoxidaton to increase to slightly more than 10%. These results indicate that more reoxidation occurred during the drying stage than during the washing stage. These observations lead to the conclusions that (1) protection of reduced samples from atmospheric O2 is essential if extensive reoxidation is to be prevented, and (2) the methods and apparatus described herein are effective for accomplishing that purpose in abiotically reduced smectites. They may also be effective if applied to microbially reduced smectites.

The heavy metal cations studied were adsorbed by hectorite suspended in 0.05 M calcium chloride as a pH-dependent reaction in the order, Cu > Zn > (Co, Mn) > Ni. The adsorption of heavy metal cations was accompanied by the removal from solution of silicic acid released by clay dissolution. It is proposed that the reaction takes place on edge surfaces such that the clay lattice is effectively extended. This result complements other work in which it has been shown that the adsorption of silicic acid by other silicate clays results in an increased adsorption of zinc, cobalt and nickel. The present study did not provide evidence of the exchange of zinc and other cations for lattice magnesium.

The solubility of hectorite was decreased in the presence of heavy metal cations in the same order that favoured their adsorption. It is proposed that they limit the dissolution of hectorite in weakly acidic solutions by adsorption on or near the sites most prone to proton attack, that is, the magnesium ions of the octahedral layer exposed at edges and defects.

The percolation of water through waste landfill sites produces leachates with large amounts of pollutants. Clay barriers are often used to limit soil and underground water pollution. A better understanding of the interaction between ammonium smectite and carboxylic acids would contribute significantly to our understanding of such systems. The SWy-2 (Wyoming smectite) was exchanged with NH4+ and then batched with carboxylic acids (acetic, formic, chloroacetic and oxalic) in concentrations between 0.01 M and 1 M. The solid phases obtained were analysed chemically and characterized by infrared absorption spectroscopy (IR) and powder X-ray diffraction (XRD). Ionic chromatography was used for the quantitative measurement of ammonium ions in the solution after the interaction. For the four acids, the interaction was characterized by a cationic exchange of NH4+ to H3O+. A partial exchange to Al3+ due to a partial dissolution of the sample in strong acidic medium was observed with chloroacetic and oxalic acids for which adsorption of molecules on the clay sample occurs, mainly through H-bonding with the cation. Moreover, the intercalation of oxalic acid in the interlayer space was highlighted.

Polycondensation reactions between amino acids and phenols are one of the pathways for the formation of humic substances, and clay minerals are able to catalyse these reactions. To investigate the catalytic power of allophane, an allophane fraction (ALF) was separated from weathered pumice (WP) that contained imogolite as an impurity by taking advantage of differences in sedimentation velocity. The iron content in the separated ALF was increased by up to 3.0% compared to that in the starting WP (1.3%), and the ALF was further treated with sodium dithionate and citric acid (ALF-DC) to remove the iron. The catalytic powers of WP, ALF and ALF-DC were evaluated, based on the degree of darkening of reaction mixtures from polycondensation reactions between catechol and tryptophan, model compounds for precursors of humic substances. The catalytic power for ALF was significantly higher than the corresponding values for WP and ALF-DC. This can be attributed to the high iron content of the ALF, which serves as a Lewis acid that can enhance nucleophilic reactions which occur during the polycondensation reactions.

Catalytic properties of Cu-doped alumina-pillared montmorillonite samples have been tested in the liquid phase oxidation of toluene, o-, m-, and p-xylene with hydrogen peroxide. The results show that the clay samples possess significant activity for both the oxidation of methyl groups and hydroxylation of the aromatic ring. Physicochemical characterization of the catalysts using XRD, BET, ESR and ICP-AES techniques show that they are porous materials with Cu species located in the interlayer, present either as isolated Cu2+ ions anchored at alumina pillars or as patches of amorphous CuO. The dependence of the overall yields on the amount of Cu dopant is discussed and explained in terms of the catalyst structural properties.

Effects of tetrahedral isomorphic substitution on the IR spectra of fluorine micas were demonstrated by comparing the spectrum of taeniolite KMg2Li(Si4O10)F2 with those of the substituted analogues, in which Ga, Al, B or Ge substituted for Si in tetrahedral sites. The e11 bands move towards lower frequencies as the content of substituted cation in tetrahedral site increases, whereas The a11 and a12 bands moves towards higher frequencies. Linear relationships were found between a12 the band frequency and the extent of tetrahedral substitutions. The magnitude of shifts per molar substitution for the a12 bands is dependent on the species of substituted cation and decreases in the order Ga > Al > Ge > B, showing an intimate correlation with the field strength z1·z2/r2M–O of the substituted cations. This implies that the polarizing power of the substituted cations has a pronounced effect on the Si-O stretching vibrations.

The clay mineralogy of sediments collected from the San Simón inlet, the Ría de Vigo, the Galician Platform, the Galician Margin and the Celtic Sea has been studied using XRD, IR and TEM with a microanalytical attachment. All samples consisted largely of dioctahedral mica and kaolin minerals, in addition to significant amounts of gibbsite, chloritic and smectitic minerals. The clay mineralogy of the sediments is generally consistent with terrigenous inputs from soils and weathered rocks of the Galician granitic hinterland. It is of particular interest that gibbsite, which is not a common constituent of soils of temperate climates, has previously been shown to occur in weathering profiles in this region and may therefore be regarded as an indicator of ‘‘continentality’’, as suggested by Macías Vásquez and co-workers. The smectitic mineral is Fe-rich and also contains significant amounts of K. This mineral is likely to be ultimately of an authigenic origin and may possibly be important as a precursor mineral in a diffuse, non-granular glauconitization process.