Structural features of very highly disordered 2:1 trioctahedral phyllosilicates from the Madrid Basin have been studied. Application of Fourier methods to XRD patterns shows that these materials consist of random kerolite-stevensite mixed-layered phases (R = 0) with 50–80% kerolite layers, and have a very small particle size with a mean of three unit-cells stacked in the c* direction. IR spectrum deconvolution in OH-stretching and librational modes seems to indicate five different types of water. Specific surface measurements (N2, BET) indicate anomalous high values (240–320 m2/g). These results suggest important catalytic and surface chemistry applications.

The surface composition of some halloysites with different particle morphology has been investigated by X-ray photoelectron spectroscopy (XPS) before and after removal of external Fe. The Fe(III) 2p3/2 binding energy of external Fe is appreciably smaller than that of structural Fe. Particle morphology is influenced by structural Fe content. The long-tubular halloysite has very little surface Fe, and its concentration tends to increase with the proportion of non-tubular particles in the samples. The spheroidal sample contains the most structural Fe which, however, does not appear to influence particle shape directly. Study by XPS indicates that Fe substitutes for Al in octahedral positions in approximately 1 : 2 proportion. As a result, an increase in octahedral vacancies and cation exchange capacity would be predicted. Further, halloysite layers within a crystal are generally inhomogeneous in composition. Built up like “onion skins”, the surface layers would either be enriched or depleted in Fe depending on the chemical environment in which crystal growth occurs.

Illite-smectite (I-S) mixed-layer minerals from North Sea oil fields and a Danish outcrop were investigated to determine the detailed structure and the diagenetic clay transformation. Clay layers in the chalk and residues obtained by dissolution of the chalk matrix at pH 5 were investigated. The phase compositions and layer sequences were determined by X-ray diffraction (XRD) including simulation with a multicomponent program. The structural formulae were determined from chemical analysis, infrared (IR) and 27Al NMR spectroscopies and XRD, and the particle shape by atomic force microscopy (AFM). A high-smectitic (HS) I-S phase and a lowsmectitic (LS) illite-smectite-chlorite (I-S-Ch) phase, both dioctahedral, together constitute 80 – 90% of each sample. However, two samples contain significant amounts of tosudite and of Ch-Serpentine (Sr), respectively. Most of the clay layers have probably formed by dissolution of the chalk, but one Campanian and one Santonian clay layer in well Baron 2 may have a sedimentary origin. The HS and LS minerals are probably of detrital origin. Early diagenesis has taken place through a fixation of Mg in brucite interlayers in the LS phase, this solid-state process forming di-trioctahedral chlorite layers. During later diagenesis involving dissolution of the HS phase, neoformation of a tosudite or of a random mixed-layer trioctahedral chlorite-berthierine took place. In the tosudite, brucite-like sheets are regularly interstratified with smectite interlayers between dioctahedral 2:1 layers, resulting in ditrioctahedral chlorite layers.

Dioktaedrische Smektite aus 19 Bentonitproben werden abgetrennt. Aus den chemischen Analysen errechnen sich unter Berücksichtigung der direkt gemessenen Zwischenschichtladungen (nach Lagaly & Weiss, 1971) kristallchemische Strukturformeln von exakt dioktaedrischen Mineralen. Die Tetraederzentren in der Struktur sind fast ausschliesslich von Si4+ besetzt; nur zwei der untersuchten Minerale zeigen eine beidellitische Komponente. Die gemessenen mittleren Zwischenschichtladungen der Montmorillonite (0·33 bis 0·39) ergeben sich allein aus der oktaedrischen Substitution von Me3+ durch Me2+. Im Gegensatz zu der grossen Variation der Strukturformeln von dioktaedrischen Smektiten in der älteren Literatur sind die kristallchemischen Unterschiede der hier untersuchten gereinigten Smektite sehr klein.

Im Vergleich zu den Rohbentoniten sind die Konzentrationen der meisten Spurenelemente in den abgetrennten Montmorilloniten erheblich verringert. Nur Mn, Zn, Co und Ni scheinen in die Kristallstruktur eingebaut zu sein. Die übrigen analysierten Spurenelemente sind adsorbtiv gebunden oder in akzessorischen Mineralen enthalten.

The transformation of schwertmannite to goethite was studied by ageing one synthetic and five natural schwertmannites in water at room temperature. Additionally, one synthetic and two natural schwertmannites were kept at variable pH (2, 4, 6 and 8). After one year, only the synthetic sample and one natural schwertmannite had transformed to goethite. However, the oxalate solubility of Fe and trace elements in all the samples decreased, whereas the total Fe/S ratios and specific surface areas of all samples increased. Arsenic and organic matter appeared to suppress the schwertmannite-to-goethite phase transformation. At pH 2, synthetic schwertmannite fully-transformed to goethite, but at pH 4–6 only minor transformation occurred. Depending on pH, many trace elements were released into solution during ageing of the natural schwertmannites. In general, Co, Mn, Zn and Si were released to solution, whereas As was enriched in the remaining iron oxide fraction. Al was dissolved at pH <4.

Single crystals of gibbsite were partially dehydrated to boehmite in a hydrothermal atmosphere. Most of the boehmite crystallites show preferred orientation that can be explained by the octahedral linkage. Further heating in air leads to a tetragonal γ-Al2O3 whose crystallites also are oriented. The orientations give information about structural details. At about 900°C a transformation γ→θ-Al2O3 takes place. In this case too the crystallites are oriented. The oxygen chains lying parallel to the a-axis of gibbsite are strongly bound and are taken over in every new lattice during transformation.

Palygorskite has been identified as a major constituent of the clay fraction in mid-Cretaceous deposits of the Meseta, the Middle Atlas, and the Rif in central and northern Morocco. Two types of palygorskite are differentiated, based on the morphology of crystallites, bio- and lithofacies associations of the containing sediments. Type 1 occurs in sections of the Meseta and the Middle Atlas, where the mineral displays bundles of long fibres under the electron microscope and is associated with shallow marine carbonate and evaporite facies. Type 2 was found in the Rif, where palygorskite occurs mostly as bundles of shorter fibres in turbiditic sediments of a supposed deep-marine environment. Associated microfossils indicate reworking of the palygorskite-bearing sediment from shallower parts of the basin. Palygorskite apparently grew authigenically in the chemically restricted environments of the Meseta and the Middle Atlas, whereas it is of a detrital origin in the Rif section. We consider that sediments containing authigenically formed palygorskite (type 1) could be the source of detrital palygorskite (type 2). Type 1 deposits on the North African shelf were probably partly reworked and responsible for the supply of palygorskite to mid-Cretaceous Atlantic basins, where the mineral is well known from several DSDP sites. As in the case of various Recent deep-sea palygorskite occurrences, aeolian transport may have significantly contributed to palygorskite supply to the ocean basins.

The usefulness of various techniques for characterizing poorlyordered inorganic gel systems in clays is considered. Many established instrumental techniques are unsuitable, but thermal methods, chemical dissolution techniques, and specific surface reactions are more appropriate. The reaction of fluoride with clays is used as an example of the latter and methods for detection and monitoring of the fluoride uptake are described. Its value is demonstrated for studying gel materials in soils and relating them to synthetic alumina-silica gels.

Fe oxides deposited in ditches draining a bog in the Harz Mountains, Northern Germany, consist essentially of a two-XRD line ferrihydrite that has a magnetic hyperfine field of only 46·5 T at 4·2 K. Pyrophosphate extraction led to an incomplete separation of this from organically-bound Fe, which was depleted in the residue and particularly enriched in the dialysate of the extract. Decomposition of humics with H2O2 led to a further depletion of organic Fe, but also increased the number of XRD lines of the ferrihydrite to six, and raised the hyperfine field by ∼1 T. These modifications are probably the result of an improved interparticle coherence.

A new practical and precise method for determining soil aggregate stability is described. Four air-dry aggregate fractions (<0.25, 0.25–0.5, 0.5–1.0 and 1.0–2.0 mm) were added to thoroughly stirred water in a Mastersizer 2000 laser diffractometer. The suspension obtained was passed directly through the measuring system. The dynamics of median (equivalent diameter d50) particle-size distribution decrease (interpolated with a logarithmic function) was assumed to be the measure of soil aggregate stability. In order to show the applicability of the new method, the results obtained (for selected and diverse soils) were compared with those from the wet sieving standard method. The main conclusion is that the proposed method is convenient and can be successfully used for the estimation of soil aggregate stability. Moreover, it has wider application because standard sieving methods are restricted to aggregates >0.25 mm whereas, with the use of the laser diffraction method, smaller aggregates can be measured. The energy delivered to the aggregates in the process of aggregate disintegration is more reproducible in the method described here. The method also provides an opportunity to verify that the soil aggregates are completely destroyed (lack of the changes of the median value shows the end of soil aggregate disintegration).

In the quantitative X-ray diffraction analysis of a series of samples, the problems arising from the variable compositions and degrees of crystallinity of clay minerals were overcome to a great extent by the use of standards extracted from the samples. Procedures are given for separation of the montmorillonite standard by differential settling of Na-montmorillonite solvated in an ethanol solution and for isolation of the kaolinite, mica, and chlorite standards by density separation of their Na-forms in thallous formate.

Calibration curves were prepared from the X-ray diffractograms obtained for series of known mixtures of Ca-forms of the standards and the internal standard boehmite using both powder and smear-oriented mounting techniques.

Delta alumina is a transition form obtained during the conversion of boehmite to corundum. Alternative methods have been found for preparing this alumina in a well crystallised condition, enabling detailed X-ray powder data to be compiled. The X-ray data are accounted for by a large tetragonal structure cell of which the axial ratio is 1·47, or 3/2 times the axial ratio of the spinel-like pseudo-cell of Saalfeld. The lattice parameters are a0=7·96 Å and c0=11·70 Å. This large cell provides an integral number of vacancies, contrasting with the 2⅔ vacancies of the pseudo-cell, and allows the atomic arrangement to be ordered.

Results from previous work on clay-mineral complexes with dimethyl sulphoxide are taken as a starting point for the development of a method to identify kaolin in the presence of chlorite. The use of this method with artificial mixtures of these minerals, and with soil clays allows the detection of kaolin when it is present in an amount higher than 5%, through the formation of a mono-layer complex with a basal spacing of 11.8 Å. Details for the use of the method are given.

The sorption and transformation of phenol, 2-methylphenol, 3-methylphenol, 2,6-dimethylphenol, 3,5-dimethylphenol, and 2,4,6-trimethylphenol, by homoionic Na-, H-, Ca-, Cu-, Al-, and Fe(III)-montmorillonite from both vapour and aqueous phases were examined by IR spectroscopy. All the phenols were sorbed by the clays but were modified to different degrees depending on the exchangeable cations and on the amount and type of alkyl substitution of the phenols. Sorption of 2,6-dimethylphenol from aqueous solution was irreversible, and the extent of sorption followed the order Fe- > Al- > Cu- > Ca-clay. Both transition and non-transition metal cations were effective in transforming the phenol sorbates and heating the clay/phenol complexes further enhanced transformation. The results are discussed in terms of the nature of the transformation products and the likely role of radical reactions in their formation.

Three soil profiles developed on a serpentinite body (La Rochel'Abeille, near Limoges) show three stages of weathering. All soils contain iron-rich smectites and secondary chlorites. The latter are very silica-rich, more so than 14 Å chlorites from crystalline rocks. In the (B)1g horizon of the hydromorphic profile, these minerals seem to give a reaction of the type:

This reaction, typical of a closed system, appears to be operative in a soil profile which is certainly, in part, open to chemical migration. The chemistry of the weathered serpentinite and the chemical composition of newly formed minerals as well as those of the serpentinite are used to indicate the chemiographic relations of clay minerals formed in the weathering profiles.

‘Epoxyphilic’ montmorillonites were prepared containing various functional groups which can react with one or both of the components in amine-cured epoxy formulations. The preparation involves the ion exchange of six organic ammonium compounds containing either carboxylic acid, anhydride, phenolic hydroxyl, alcoholic hydroxyl, amide or amine functional groups. X-ray diffraction, elemental analysis and FTIR studies confirm the intercalation of the organic cations to form epoxyphilic montmorillonites. The adsorption behaviour of the modified montmorillonites are compared with the unmodified montmorillonite in an epoxy resin before and after the curing process.

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.

Ammonium-rich illite was identified in shales from the meta-anthracite coalfields of Zemplinicum (the Western Carpathians) together with K-illite and Na-illite using X-ray diffraction (XRD), infrared absorption and chemical analyses. The NH4-abundance in illite was quantified by the position of the 005 XRD reflection and by chemical analysis. Ammonium-bearing illite was probably formed in the temperature interval 200-270°C by illitization of a kaolinite precursor in the presence of ammonium.

Photochemical isomerization of azobenzene intercalated in the hydrophobic, interlayer spaces of swelling fluor-tetrasilicic micas exchanged with dialkyldimethylammonium ions, with the alkyl chain length from 10 to 18, was investigated. Thin films of the organoammonium-mica-azobenzene intercalation compounds were obtained by depositing a suspension of the organoammonium-micas (prepared using a toluene/methanol solution of azobenzene) on quartz substrates. The intercalated azobenzene showed reversible photochromic reactions induced by UV and visible light irradiation. The fraction of the photochemically formed cis-isomer in the photostationary states decreased with a decrease in temperature. The observed change in the photochemical reactions is thought to reflect changes in the states of the dialkyldimethylammonium ions in the interlayer space of the swelling fluor-tetrasilicic mica.

Pore-lining chlorite is common in Rotliegend lake shoreline aeolian sandstones from northern Germany and preserves abnormally high primary intergranular porosity. In the north of the study area, in a basinward direction, the chlorites are Mg-rich while towards the south they become Fe-rich over a distance of about 15 km. All are unusually rich in Mn. Magnesium-rich examples tend to be more abundant than illite, while Fe-rich examples cover framework grains less continuously and are admixed with more abundant illite. Oxygen isotope analysis of 30 chlorites in the 2–6 µm fraction gave δ18O (SMOW) values of 7 to 12‰ (mean 9.8‰). These data show no obvious trend across the study area, nor in relation to changes in chlorite composition, or burial depth.

The honeycomb arrangement of chlorite crystals suggests chlorite formation via the sequence smectite-corrensite-chlorite. Chlorite distribution and the systematic changes in its composition suggest that formation of a precursor was related to lateral migration of Mg-rich fluids from basinal shales and/or evaporites during shallow burial. Interaction of these fluids with early formed oxyhydroxide coatings on the aeolian sand grains provided a source of Fe and the Mn. The isotope data suggest that the eventual formation of chlorite during deep burial occurred from waters with positive δ18O values, comparable to those present during the deep burial formation of illite.