Structural iron in smectites correlates with the cell edge length b and increases the refractive index. The cell edge length b is usually obtained from the position of the (060) reflection, but in this work we show that such b values differ from the values obtained from Rietveld fits because contributions from (hkl) reflections shift the position of the (060) reflection. The correlation between Fe and cell edge length b was significant (r2 > 0.99); the relationship is b [Å] = 8.9977(0.0035) + 0.1117(0.0032) × Fetot. Furthermore, we present for the first time measurements of the refractive index n of Fe-bearing smectites, applying a recently published turbidity method (Weidler & Friedrich, 2007). The refractive index correlates both with structural iron (r2 = 0.64) and with b (r2 = 0.94).

The increase of the absorption efficiency of boron (B) by plants is essential for increasing crop productivity. The intercalation of B in MgAl layered double hydroxides (LDHs) is an alternative to evaluating how these materials can provide B to plants. In this work, a MgAl LDH intercalated with borate ions (Mg2Al-B-LDH) was synthesized by the constant pH coprecipitation method, and the material produced was evaluated as a matrix for storage and as a source of B for plants. The Mg2Al-B-LDH was characterized by XRD, ATR-FTIR, TGA-DTA, specific surface area, pore size and volume, and SEM. A bioassay was performed to verify the supply of B to plants from the two sources in the forms of H3BO3 and of Mg2Al-B-LDH to sunflower plants grown in pots. The LDH basal spacing value of 12.0 Å is characteristic of intercalation of tetraborate octahydrate ions [B4O5(OH)42−]·8H2O between the layers. There was an increase in the dry matter (DM) and B content of the plants relative to those treatments where no B was added. The lack of statistical difference for plant yield between the two sources of B suggests a lack of stability of the Mg2Al-B-LDH structure under the acidic condition of the soil.

The adsorption of the large cationic alkaloid berberine by montmorillonite in aqueous suspensions was investigated. An adsorption isotherm of berberine and desorption isotherms of exchangeable Na+, K+, Mg2+ and Ca2+ were determined by chemical analysis of the non-adsorbed berberine and the released cations in the supernatants. The isotherms suggest that the adsorption of berberine takes place in two different types of reaction mechanism: (1) cation exchange, and (2) a secondary organophyllic adsorption. The cation exchange occurring first is followed by the secondary adsorption which is accompanied by Cl- adsorption. Monovalent cations are exchanged before the divalent cations.

Samples loaded with increasing amounts of berberine were examined by X-ray diffraction at room temperature, and after gradual heating up to 420°C. The basal spacing of the loaded samples after the thermal treatment became 1.28 nm, indicating the formation of carbon in the interlayer, thus proving that the adsorbed berberine was located in the interlayer space. At room temperature the basal spacing of samples loaded with 8 and 15 mmol of berberine per 100 g of clay was 1.28–1.30 nm indicating that in the interlayer space berberine cations were lying parallel to the alumino-silicate layers. The basal spacing of a sample with 36 mmol of berberine per 100 g of clay was 1.48 nm. This spacing does not give conclusive information on the arrangement of berberine in the interlayer. The spacing of samples with 57–147 mmol of berberine per 100 g of clay was 1.59 nm, suggesting the presence of bilayers of berberine in the interlayers. During thermal dehydration, the spacing of samples with 36–73 mmol of berberine per 100 g of clay decreased, but that of samples with 105–147 mmol of berberine per 100 g of clay increased to 1.66 nm. These samples contain organophilic adsorbed berberine and it is suggested that due to the thermal treatment berberine was tilted relative to the TOT lamellae, with anhydrous Cl- between the berberine cations.

Image analyses, carried out on thin sections made in consolidated and sheared kaolinite test pieces, allow the identification of three ‘microstructural domains’: (1) the initial isotropic matrix; (2) a partly anisotropic matrix resulting from simple particle arrangement; and (3) an anisotropic matrix resulting from rearrangement plus flattening and delamination of particles.

In order to explain the micromechanisms of the clay matrix behaviour, this paper proposes to link the ‘microstructural domains’ represented in the e vs. log p Cam-clay diagram and domains of hydraulic conductivity in the k vs. e diagram.

The hydraulic conductivities are calculated following the Kozeny-Carman relations, which take into account the micro-arrangement of particles via a tortuosity calculation. The generation of 2D images shows that the preservation of the isotropic arrangement of particles is limited by a minimum porosity value. A decrease of the porosity value below this limit can be explained only by a progressive anisotropic rearrangement of the particles.

The microtexture behaviour, induced by the superimposition of the compaction, orientation and particle flattening and delamination stages, causes an anisotropy of the hydraulic conductivity which affects (1) the interstitial water flow direction, (2) the rotation of particles itself, and (3) the damage mechanism of the clay.

Seven natural clay minerals (two kaolinites, three montmorillonites, a hectorite and a palygorskite) were tested for their cytotoxicity in vitro using an established cytotoxicity assay. Cellular viability, levels of lactate dehydrogenase, N-acetyl-β-d-glucosaminidase, lactic acid and total cellular protein were measured in cells of the macrophage-like cell line, P388D1, after 48 h incubation with each clay. There was a significant relationship between BET/N2 surface area of the clays and cytotoxicity but in two cases the level of cytotoxicity was apparently influenced by the presence of quartz or cristobalite in the samples. Results are discussed in the light of the available animal and epidemiological data relating to clay minerals.

Biodegradable chitosan/bentonite composites with three different compositions were synthesized by the intercalation method using cetyltrimethylammonium bromide as the cationic surfactant. The composites were characterized using conductivity, density, particle size measurements, FTIR, TGA, XRD and SEM methods. Colloidal stabilities of the suspensions prepared in silicone oil (SO) were observed to increase with decreasing density. The effects of dispersed particle concentration, shear rate, electric field strength, electric field frequency and temperature on the electrorheological (ER) activities of the suspensions were investigated. The electric field viscosities of the suspensions showed typical shear thinning non-Newtonian viscoelastic behaviour. Yield stresses of the suspensions were observed to change in proportion to the square of applied electric field (E). Further, according to creep and creep-recovery analysis, reversible viscoelastic deformations were observed in the suspensions under E ≠ 0 kV mm–1.

Sorption isotherms of ethylene glycol monoethyl ether (EGME) on homoionic Na−, K−, Mg− and Ca-montmorillonites at 25°C were determined. The extent of sorption was found to depend on the exchangeable cations, being larger for the bivalent ionic forms. Uptake of EGME was compared with the retention value obtained by evacuation of the sample wetted with EGME and also interpreted from XRD data. The results indicate that the montmorillonite-EGME complex formed by sorption at the saturation vapour pressure is stable and less ambiguous than after wetting by EGME. Montmorillonites are not suitable reference materials for surface area measurements.

L'étude concerne 225 échantillons d'âge Jurassique à actuel de l'Océan Atlantique. La comparaison de l'abondance des smectites lattées, estimée sur micrographies électroniques, et de divers paramètres des sédiments, apporte des informations nouvelles sur la genèse et la signification de ces minéraux dans des sédiments non volcanoclastiques et non remainés. L'élaboration des smectites lattées par recristallisation diagénétique de smectites détritiques est favorisée lorsque la microperméabilité du sédiment est réduite (argiles fibreuses et particules calcaires, surtout les foraminifères, peu abondantes); lorsque les échanges chimiques à bilan constant avec le milieu interstitiel sont facilités (smectites abondantes) et lorsque la vitesse de dépôt est faible à moyenne. Dans les autres cas, la recristallisation de smectites lattées est très réduite ou absente. L'identification de ces minéraux dans les sédiments permet de préciser les conditions paléogéographiques de dépôt. La rareté des smectites lattées au Plio—Quaternaire pourrait être liée à l'extension des grands refroidissements mondiaux du climat.

A profile within the Upper Freshwater Molasse (OSM) of eastern Switzerland was sampled. Particle-size analyses, bulk chemical analyses, cation exchange capacities and Fe fractions (oxalate- and dithionite-citrate-bicarbonate-soluble Fe, total Fe) were measured. The mineralogical composition was determined by X-ray diffraction and quantified with Rietveld analysis. The layer charge of selected fine-clay samples was determined with the alkylammonium method using chain nc = 12. The profile could be divided into a lower sequence (I) and an upper sequence (II) by a hiatus. Chemical data, particle-size distributions and calcite contents indicated that soil formation was essentially restricted to wetting-drying cycles associated with redox cycles evident from Feo/Fed and Fed/Fet ratios. A significant correlation between the d060 values of the dioctahedral smectite-illite mixed-layer phases and Feo/Fed was interpreted as the influence of microbial Fe3+ reduction, which affected both the Fe oxides and Fe-rich clay minerals. This is the first evidence that the Fe dynamics of both mineral groups may be linked. The amount of illitization also correlated with Feo/Fed, but only in the upper part of the profile. This indicates that wetting-drying cycles were necessary for the illitization process.

Tonsteins, which are kaolinite-rich rocks with an amorphous groundmass containing much organic material, occur widely in European Coal Measure deposits. The nature of these rocks and their peculiar fabric is considered in detail and evidence is adduced which suggests that they were derived from soils and that the original organic components (micro-organisms and fungi) played a significant part in the formation of the kaolinite macrocrystals.

Sixteen glauconite samples from different locations in Belgium and Northern France were investigated by 57Fe Mössbauer spectroscopy at room temperature. The spectra were fitted with three Fe3+ and two Fe2+ doublets, both Fe species occupying M1(trans) and M2(cis) sites in the T-O-T layers. The third Fe3+ doublet was assigned to interlayer ferric complexes. The observed Mössbauer parameters did not show significant variations from sample to sample. No direct relation between K and Fe content was observed, although within some distinct groups (e.g. Bande Noire, Cenomanian) the amount of Fe2+ increased with increasing K content.

A near infrared (NIR) spectroscopy approach was undertaken to collect information on the Al cationic distribution in tetrahedral and octahedral sites in natural chlorite (clinochlore) samples. Structural formulae were established using electron microprobe and Mössbauer spectroscopy. A band located near 7115 cm–1 was attributed to the overtone of OH fundamental stretching mode of Mg2AlOH and increases with the total Al amount. Good correlation was obtained between the (SiAl)O–OH vibration band area and tetrahedral Al content, making it easy to partition Al (and thus Fe3+) between octahedral and tetrahedral sites.

Separate montmorillonite suspensions were treated with CrCl3 to give seven Cr(III) concentrations. Each suspension was then titrated with 0.1 N NaOH to give a NaOH/Cr3+ molar ratio of 2.5. Montmorillonite was an effective sorbent for hydroxy-Cr species up to 1200 cmol(+)/kg; above that concentration, sorption continued, though less efficiently. However, N2-BET specific surfaces and cation exchange capacity measurements indicated that the montmorillonite could sorb significantly more than 1200 cmol(+)/kg. There was virtually no exchangeable Cr in any of the clays, suggesting that this element was covalently bonded to the siloxane surface. Infrared spectroscopy revealed a vibration at 1015–1020 cm–1 in the Cr clays which was not present in the control. This new absorption band was attributed to an attenuation of the Si–O a11 vibration caused by inner-sphere complexation of the interlayer Cr with the siloxane oxygen. Because Cr was strongly held and efficiently sorbed, montmorillonite was shown to be an effective sorbent for hydroxy-Cr polymers.

Clay mineral analysis of Spodosols collected from the Adirondack Mountains reveals that smectite is common in the forest floor and uppermost soil horizons (the O, A and E horizons) and probably forms from the transformation of vermiculite via a low-charge vermiculite intermediate. The conversion of vermiculite to smectite occurs in the upper part of the soil profile where organic acids and strong inorganic acids (derived from atmospheric deposition) combine to create an intense weathering environment. X-ray diffraction (XRD) and chemical data for the clay fraction indicate that both the smectite and the low-charge vermiculite are Al-rich and dioctahedral. The smectite appears to be a beidellite. Transformation of vermiculite to smectite may have progressed in these acidic horizons by net layer-charge reduction resulting from the progressive substitution of Si for Al. The parent material for the soil clays was probably biotite, but little remains in these soils.

The colloidal state (sol, flocs, gels) of Na-montmorillonite dispersions (from bentonite from Bavaria, Germany) was adjusted by the addition of poly(ethylene oxides) with terminal trimethylammonium groups. The colloidal state of the dispersions changed with the molar mass of these end-capped poly(ethylene oxides). The sol-gel diagrams (up to 4.5% (w/w) montmorillonite) in the presence of TMA-PEO 1500 and TMA-PEO 4000 (up to 40 g/l) were characterized by large fields of gel whereas TMA-PEO 20000 and TMA-PEO 35000 caused peptization by steric stabilization. Even dispersions with the highest montmorillonite content (4.5%) were peptized by >0.2 g/l TMA-PEO 35000. The critical coagulation concentration of NaCl was increased by the polymer addition, but the increase was modest (from 8-12 mmol/l to 50 mmol/l). The changes of the colloidal state, the flow behaviour and the salt coagulation reveal the sensitive interplay between stabilization mechanisms (electrostatic, steric) and destabilization effects (bridging, charge compensation, depletion flocculation).

Mudstones and claystones from the southern marginal area of the European Upper Triassic, midcontinental Keuper basin (Silesia, southern Poland) were investigated using XRD, organic and inorganic geochemistry, SEM, K-Ar of illite-smectite, AFT, and stable isotopes of O and C in carbonates in order to unravel the consequent phases of the geological history of these rocks, known for abundant fossils of land vertebrates, and in particular to evaluate the diagenetic overprint on the mineral composition. The detected and quantified mineral assemblage consists of quartz, calcite, dolomite, Ca-dolomite, illite, mixed-layer illite-smectite, and kaolinite as major components, plus feldspars, hematite, pyrite, chlorite, anatase, siderite, goethite as minor components. Palygorskite, gypsum, jarosite and apatite were identified in places.

The K-Ar dates document a post-sedimentary thermal event, 164 Ma or younger, which resulted in partial illitization of smectite and kaolinite. The maximum palaeotemperatures were estimated from illite-smectite as ∼125°C. Apatite fission track data support this conclusion, indicating a 200–160 Ma age range of the maximum temperatures close to 120°C, followed by a prolonged period of elevated temperatures. These conclusions agree well with the available data on the Mesozoic thermal event, which yielded Pb-Zn deposits in the area. Organic maturity indicators suggest the maximum palaeotemperatures <110°C.

Palygorskite was identified as authigenic by crystal morphology (TEM), and calcite by its accumulation in soil layers and by its isotopic composition evolving with time, in accordance with the sedimentary and/or climatic changes. Dolomite isotopic composition indicates more saline (concentrated) waters. Palygorskite signals a rapid local change of sedimentary conditions, correlated with algal blooms. This assemblage of authigenic minerals indicates an arid climate and the location at the transition from a distal alluvial fan to mudflat.

Fe-rich smectite, kaolinite, and hematite were products of chemical weathering on the surrounding lands and are therefore mostly detrital components of the investigated rocks. Kaolinite crystal morphology and ordering indicates a short transport distance. Hematite also crystallized in situ, in the soil horizons. A large variation in kaolinite/2:1 minerals ratio reflects hydraulic sorting, except of the Rhaetian, where it probably signals a climatic change, i.e. a shift in the weathering pattern towards kaolinite, correlated with the disappearance of hematite. Quartz, 2M1 illite, and minor feldspars and Mg-chlorite were interpreted as detrital minerals. The documented sedimentation pattern indicates that in more central parts of the Keuper playa system, where an intense authigenesis of the trioctahedral clays (chlorite, swelling chlorite, corrensite, sepiolite) took place, illite and smectite were the dominant detrital clay minerals.

Cr/Nb and Cr/Ti ratios were found as the best chemostratigraphic tools, allowing for the correlation of all investigated profiles. A stable decrease of these ratios up the investigated sedimentary sequence is interpreted as reflecting changes in the provenance pattern from more basic to more acidic rocks.

The electrical conductivity of synthetic zeolites, types X and Y has been studied to give information about the distribution and possibility of migration of the exchangeable cations, located at various sites. The Na+ samples were exchanged with K+, Cs+, Ag+, Li+, and NH4+. The various cationic forms were pressed into pellets and treated at 430°C under high vacuum for 24 hours. After cooling, the electrical conductivity and capacity was measured as a function of frequency (500–20,000 c/s) at various temperatures from −20°C up to 500°C. For each sample the reversibility was investigated. The experimental results allow the calculation of the specific conductivity, the real (ε′) and imaginary (ε″) part of the complex dielectric constant (ε*) and the loss factor tgδ.

The results show an ionic conductivity: the specific conductivity depends on the nature of the exchangeable cations as follows: Cs+ > K+ > Ag+ > Na+ > Li+. There is a different conductivity mechanism in the high temperature region compared with the low temperature region. At high temperatures (T > 400°K) the activation energy is independent of frequency. At low temperatures, a dielectuc absorption phenomenon occurs. The activation energy, calculated for this process was somewhat higher, but of the same order of magnitude as that of the high temperature region. It is suggested that the migration of the exchangeable cations in the supercage to interstitial positions gives rise to this dipole absorption phenomenon.

A comparison of the decationated Y zeolites with Na+Y and Na+X made it possible to attribute the conductivity to the cations in the supercage only. The exchangeable cations in the cubo-octahedra and in the hexagonal prisms lower the activation energy of the moving cations. Thus the energy of activation of X zeolites is lower than of Y zeolites.

Metamorphic isograd surfaces are mapped within the Morcles nappe using illite crystallinity (IC) and (clay-) mineral parageneses in 268 samples. The diagenesis-anchizone and the anchizone-epizone boundaries are nearly vertical surfaces which crosscut the present-day recumbent fold nappe structure. Frontal parts of the nappe are diagenetic (Tmax <200°C) whereas rear parts both in the normal and inverted limb are epizonal (Tmax >300°C). We demonstrate that the calcite content of shales, marls or limestones has no influence on the average IC. Deviations of individual samples from the mean IC of any given diagenetic and lower anchizonal site are very large, however, without it being possible to associate deviations with any obvious rock parameter. The standard deviations of populations of IC values decrease strongly with increasing metamorphic grade (toward smaller IC values). Mapping the diagenesis-anchizone boundary requires a much larger sampling effort than the same exercise for the anchizone-epizone boundary.

It is suggested (1) that large amounts of Al, Fe and Si carried in solution by fresh water are chemically precipitated as hydroxide gels in the brackish water environment of estuaries and deltas, and (2) that these gels are subsequently deposited in both the brackish water environment and in the neighbouring seas, where they become parental material for the neoformation of clay minerals, and various other silicate and iron minerals. The types of neoformed minerals will depend upon both the composition of the parental gels and the physico-chemical milieu of their crystallization. Evidence is discussed supporting this hypothesis from the following sources (1) the concentrations of Al, Fe and Si dissolved in fresh water and in sea-water, (2) experimental work on the crystallization of alumino-siliceous gels, and (3) a study of the precipitation of Si from the waters of the Mississippi River delta.

Because of the unusual sediment pattern of present times, this source of neoformed clay minerals and other minerals contributes only a small proportion of the sediments of the brackish parts of estuaries, deltas and the adjacent seas, which are dominated by fine-grained continental detritus. In earlier geological eras, when the world's river systems carried only relatively minor amounts of fine-grained continental detritus, this source of neoformed minerals is likely to have contributed a considerable proportion of the fine-grained sediments of these areas of sedimentation. Three possible examples are discussed.