bluuebunny/crossref_metadata_2025 huggingface dataset:
Utilisation de la diffractometrie X pour la determination des constituants amorphes dans les sediments marins (silice biogene et cendres volcaniques)
Authors: Lapaquellerie Y.
Published: December 2006

Resume

La détermination des complexes silico-ferriques, hydroxydes métalliques ou autres matériaux amorphes ou pseudocristallins contenus dans les sédiments marins est généralement difficile. La méthode décrite utilise la diffractométrie de RX et permet l'analyse quantitative de quelques-uns de ces matériaux tels que la silice biogène ou les cendres volcaniques. Cette phase amorphe constitue une composante majeure dans certains sédiments marins, d'où la nécessité de pouvoir la quantifier. La méthode reste suffisamment simple, fiable et précise pour permettre aussi la détermination quantitative de la phase cristallisée qui lui est généralement associée.
Analysis of cation distribution in dioctahedral micaceous minerals on the basis of IR spectroscopy data
Authors: Besson G. , Drits V. A. , Daynyak L. G. , Smoliar B. B.
Published: December 2006

A method is described for IR spectroscopy whereby combining statistical analysis with the quantitative method described by Slonimskaya et al. (1986) results in more informative spectra. Application of this method to dioctahedral micaceous minerals with vacant trans octahedra has revealed a number of peculiarities in the octahedral cation distribution. This distribution is never completely disordered in the samples studied and shows maximum degree of short-range order in minerals having predominant Al.
Oxidative decarboxylation of isocitric acid in the presence of montmorillonite
Authors: Naidja A. , Siffert B.
Published: December 2006

Isocitric acid oxidative decarboxylation was realized in the absence and in the presence of homoionic Na+-, Mn2+-, and Cu2+-montmorillonite. The catalytic activity of the clay depends upon the nature of the interlayer exchangeable cation. Isocitric acid is transformed into α-ketoglutaric acid under the action of the clay mineral saturated with Na+ cations which do not form a complex with the isocitrate anion. Nevertheless, the reaction rate is very much lower than in the presence of the enzymatic system (isocitrate dehydrogenase enzyme and nicotinamide adenine dinucleotide phosphate coenzyme). The reaction mechanism in the presence of clay is given showing the different steps of the transformation.
Structural transformations of kaolins into (Ni, Al) serpentine-like phases and subsequently into trioctahedral micas under hydrothermal conditions
Authors: Frank-Kamenetskii V. A. , Goilo E. A. , Kotov N. V. , Rieder M.
Published: December 2006

It has been shown that clay minerals transform into (Mg, Al) or (Ni,Al) serpentine-like phases if treated hydrothermally in the presence of MgCO3 or NiCO3 (Shitov et al., 1974, Frank-Kamenetskii et al., 1978, 1983a,b; Kotel'nikova et al., 1976; Varela et al., 1983; Kotov et al., 1985; Ryumin et al., 1978) and that the polytypism of the initial kaolins is inherited by the products. It has also been shown that (Mg,Al) serpentine-like phases react with KC1 to form dioctahedral micas and Mg-rich serpentine phases, but the latter do not react to trioctahedral micas (Kotel'nikova et al., 1976). Consequently, it was desirable to look for mechanisms for obtaining trioctahedral micas from serpentine-like phases.
Surface properties and clay mineralogy of hydrated halloysitic soil clays. I: Existence of interlayer K+specific sites
Authors: Delvaux B. , Herbillon A. J. , Dufey J. E. , Vielvoye L.
Published: December 2006

Six deferrated clay (<2 µm) samples from the major B horizons of pedons derived from basaltic pyroclasts (Western Cameroon) were selected. These soil clays, which differ mainly in their contents of halloysite and kaolinite, represent the types of secondary constituents characteristic of different weathering stages in soils derived from such volcanic materials under humid tropical conditions. On these clays, Ca2+-K+exchange equilibria were performed at pH 6 and 0·01nchloride concentration. The amounts of K+specific sites were estimated through a two-site modelling of the exchange isotherm curves. The total and external surface areas of the clays were measured by EGME retention and by the BET treatment of the N2adsorption isotherm, respectively. Relative halloysite content was found to be directly related to all measured surface charge properties,i.e.CEC, amount of K+specific sites, and total and internal surface areas. It was also observed that thermal collapse of halloysitic layers reduced both the CEC and the amount of K+specific sites. All the surface properties observed point to the presence of smectite units intimately associated with halloysite in these clays. The results further suggest that the layer charge of these smectite units differs in different samples.
Formation of synthetic analogues of double metal-hydroxy carbonate minerals under controlled pH conditions: I. The synthesis of pyroaurite and reevesite
Authors: Hansen H. C. B. , Taylor R. M.
Published: December 2006

Two-layered Fe(III)-M(II) hydroxy carbonates (M(II) = Ni or Mg) have been synthesized by induced hydrolysis using controlled air oxidation of an aqueous Fe(II)-M(II) mixture (M(II)/Fe(II) ratio >3) at a pH below which the hydroxide of the M(II) cation precipitates. The crystalline, homogeneous product can be a single phase consisting of very thin circular to hexagonal plates (0·2–0·8 µm diam.). For synthetic reevesite (Ni(II)-Fe(III) hydroxy carbonate), stable spherular aggregates are formed. The well crystallized products have an M(II)/Fe(III) ratio of about two. However, by varying the pH, the initial M(II)-Fe(III) ratio and the oxidation rate, the M(II)/Fe(III) ratio in the product and its crystallinity can be varied. The derived formulae are in reasonable agreement with the known composition of pyroaurite-type compounds. Possible synthesis pathways are discussed. The ability to control some physical and morphological features of the products indicates that the synthesis technique could prove advantageous in the preparation of certain catalyst precursors.
Magnetic ordering in Garfield nontronite under applied magnetic fields
Authors: Murad E. , Cashion J. D. , Brown L. J.
Published: December 2006

Mössbauer spectra of Garfield nontronite H33a were taken at temperatures between 2·5 and 37 K under longitudinally applied magnetic fields up to 9 T. While no magnetic order was apparent in the absence of an applied field above 7 K, the application of external magnetic fields led to the induction of magnetic hyperfine splitting up to at least 19 K. Variation of the applied fields allowed determination of hyperfine fields of bulk nontronite, and indicated the bulk sample to have a Néel temperature of about 20 K. The non-ideal behaviour of this nontronite, leading to the lack of magnetic order in the absence of applied magnetic fields, is in line with the frustration of antiferromagnetic order in the octahedral sheets due to the presence of about 6% of the iron content in tetrahedral sites, although some influence of magnetic dilution cannot be excluded.
Spectroscopic (ESR, EXAFS) evidence of Cu for (Al-Mg) substitution in octahedral sheets of smectites
Authors: Mosser C. , Mestdagh M. , D'Ecarreau A. , Herbillon A. J.
Published: December 2006

ESR has been used to obtain information on the octahedral or interlamellar position of Cu(II) in natural smectites from Burkina Faso (West Africa). On the basis of 060 XRD reflections and chemical data, these smectites were found to be Al-rich and dioctahedral. After both Mehra & Jackson, and De Endredy deferrification treatments, the Cu contents remained high (4500 and 22000 p.p.m., respectively). The Cu(II) ESR spectra of these deferrated smectites were compared to those of two reference smectites for which the structural position of Cu(II) was precisely known. The interlayer Cu(II) signal was obtained on a Cu-saturated Camp Berteau montmorillonite, while the octahedral Cu(II) signal was obtained on a synthetic Cu-rich smectite. For this latter reference sample, EXAFS spectroscopy provided evidence that Cu was in six-fold coordination in the octahedral sheet only, and was not exchangeable. In agreement with the experiments by Clementz, Pinnavaia and Mortland, a shift in the g⊥ ESR signal was observed when the air-dried Cu-saturated Camp Berteau montmorillonite (g⊥ = 2·05) was soaked in water for 48 h (g⊥ = 2·13). A small shift in the opposite sense was observed for the synthetic Cu smectite (g⊥ = 2·05 for the air-dried sample, g⊥ = 2·02 for the water-soaked sample). For the two natural smectites a small shift similar to that for the synthetic Cu-smectite was observed. These results indicate that up to 10% of the Cu atoms substitute for Al-Mg-Fe atoms in the octahedral sheets of the smectites studied.
A two-stage model for the formation of clay minerals from tephra-derived volcanic glass
Authors: Hodder A. P. W. , Green B. E. , Lowe D. J.
Published: December 2006

The kinetics of clay formation in buried paleosols developed from late Quaternary rhyolitic tephra layers near Rotorua, New Zealand, can be described in terms of a combination of parabolic and linear kinetics, reflecting the hydration of glass, and the formation of clay minerals, respectively. Such a model is consistent with the formation of clay minerals showing an Arrhenian temperature dependence and suggests, on the basis of calculated activation energies, that the process of formation of Al-rich allophane (imogolite) is diffusion controlled, whereas the rate of formation of Si-rich allophane is controlled by the chemical processes at the site of reaction.
Long-term weathering of silicates in a sandy soil at Nordmoen, southern Norway
Authors: Teveldal S. , Jørgensen P. , Stuanes A. O.
Published: December 2006

Weathering processes have been studied in a podzol profile developed on sand during a postglacial period of 9400 years. Due to disintegration of rock fragments, the particle-size distribution has changed markedly in the upper part of the profile, and minerals have been transferred from sand fractions to silt and clay fractions. The most important weathering processes are the total breakdown of trioctahedral chlorite and biotite, and the transformation of dioctahedral mica (muscovite-phengite) to a regularly interstratified mineral, and further to Al-vermiculite or smectite. By using quartz as an internal standard, the annual loss due to weathering was found to be 3·2 g/m2. The release of elements due to silicate weathering was calculated from depletion curves, and the average annual release of Na + K + Mg + Ca for the postglacial period was 19 mEq/m2.
Study of the water-bentonite system by vapour adsorption, immersion calorimetry and X-ray techniques: II. Heats of immersion, swelling pressures and thermodynamic properties
Authors: Kahr G. , Kraehenbuehl F. , Stoeckli H. F. , Müller-Vonmoos M.
Published: December 2006

A number of thermodynamic properties were obtained from the determination of adsorption isotherms and enthalpies of immersion for systems with water and Na- and Ca-bentonites. Entropy differences were calculated by combining the enthalpies of immersion and the changes in free energy derived from the adsorption isotherms. The swelling pressures, also calculated from the water adsorption isotherms, are in satisfactory agreement with the experimental data.
Some Comments on the Chemistry and Stability of Interstratified Illite-Smectite and the Role of Ostwald-Type Processes
Authors: Primmer T. J.
Published: December 2006

Much emphasis has been placed recently on the role of Ostwald-type processes (both ripening and the step rule) in the formation of interstratified illite-smectite clay minerals during diagenesis. Closer investigation of the relationships between illite particle thickness (as defined in terms of the fundamental particle theory) and particle chemistry show that simple Ostwald ripening is too simplistic a mechanism to describe observed changes in illite thickness and composition. In addition, available thermodynamic data on clay minerals suggest that the conventional notion of metastability associated with Ostwald's step rule is an inaccurate description of the relationship between illitic clay minerals and their macroscopic 2 : 1 phyllosilicate analogues.
An Unusually Interlayered Clay Mineral from the Eluvial Horizon of a Humus-Iron Podzol
Authors: Bain D. C. , Fraser A. R.
Published: December 2006

The <2 µm fraction from the eluvial horizon of a humus-iron podzol is composed predominantly of a dioctahedral mineral with a basal spacing of 14.7 Å which contracts to 13.7 Å on solvation with glycol, and to 11.4 Å on heating to 300°C. The interlayer region is partially filled with an amorphous organo-Fe-Al complex which is very unstable and is affected by every treatment employed, even homoionic cation saturation. The mineral has a mica-like morphology, contains 3.4% non-exchangeable K2O and is considered to be an interstratified mica-vermiculite formed by the weathering of mica. The contraction of the basal spacing with glycol is probably due to water being removed from the interlayer region of the vermiculite component, leaving only the natural organo-complex in the interlayer; alternatively, the contraction may be more apparent than real, resulting from an interstratification effect. Treatment with H2O2results in partial expansion with glycol.
Comparison of Measured and Calculated Diffusion Coefficients for Iodide in Compacted Clays
Authors: Oscarson D. W.
Published: December 2006

An understanding of the behaviour of contaminants in compacted clays is important in assessing the effectiveness of clay-based barrier materials used in many waste containment strategies. Here the diffusion and sorption behaviour of I−with selected compacted clays is examined (129I is a relatively long-lived radioisotope present in high-level nuclear fuel waste.) Diffusion coefficients,D, and distribution coefficients,Kd, were measured for I−with four clays: bentonite, Lake Agassiz clay (a glacial lake clay composed mainly of smectite, illite, kaolinite, and quartz), interstratified illite-smectite, and kaolinite. For the diffusion experiments the clays were compacted to a dry bulk density, ρ, of ∼1.2 Mg m−3. The mean measuredDvalues,Dm, were as follows: bentonite, 310 µm2s−1; Lake Agassiz clay, 0.62 µm2s−1; illitesmectite, 190µm2s−1; and kaolinite, 74µm2s−1. The measured values were compared with those calculated,Dc, from the following model:D=Doτan/(n+ρKd), whereDois the diffusion coefficient in pure bulk water,τathe apparent tortuosity factor, andnthe solution-filled porosity of the clay. Except for the Lake Agassiz clay, whereDmwas about an order of magnitude lower thanDc, theDmandDcvalues agreed within a factor of about two. The Lake Agassiz clay has a markedly higher organic carbon content than the other three clays, and this could affectτa, which may be overestimated in the model.
The Effect of Thermal Treatment on the Properties of Hydroxy-Al and Hydroxy-Ga Pillared Montmorillonite and Beidellite
Authors: Kloprogge J. T. , Booy E. , Jansen J. B. H. , Geus J. W.
Published: December 2006

The pillaring process of montmorillonite and beidellite with Al and Ga polymers has been studied using XRD, IR,27Al,71Ga, and29Si MAS NMR, TGA, TEM, N2adsorption and chemical analyses. The Al adsorption maximum for montmorillonite is close to 5.5 mEq Al/g clay, whereas the maximum for Ga is higher. Basal spacings of both Ga- and Al-pillared clays vary between 16.7 and 18.8 Å. Freeze-drying of pillared products followed by calcination yielded more regular pillared structures. Pillaring montmorillonite increased the BET surface area from 35 m2/g to 350 m2/g mainly by the creation of micropores <20 Å in diameter. The Al-pillared clays are thermally stable to ∼700°C. Calcination of pillared montmorillonite liberates protons from the pillar, which diffuse into the clay sheet, lowering the thermal stability. In pillared beidellite, mainly silanol groups are formed by breaking Si-O-Al bonds. No reaction is observed between pillars and montmorillonite upon calcination, whereas in pillared beidellite a structural transformation links the pillar to inverted tetrahedra of the tetrahedral sheet. The basal spacing of Ga-pillared montmorillonite collapses to 9.5 Å at 350°C due to the Ga polymer decomposing to Ga3+cations.
Synthesis and Characterization of ‘Epoxyphilic’ Montmorillonites
Authors: Akelah A. , Kelly P. , Qutubuddin S. , Moet A.
Published: December 2006

‘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.
The Competitive Adsorption of Methylene Blue on to Montmorillonite from Binary Solution wih Thioflavin T, Proflavine and Acridine Yellow. Steady-State and Dynamic Studies
Authors: Breen C. , Rock B.
Published: December 2006

Methylene blue (MB) has been used as a probe molecule to examine how the uptake dynamics and the equilibria between this dye and the surface of Na+- and H+- montmorillonite were affected by the presence of a second dye. To prevent spectral interference, the yellow dyes thioflavin T, TFT, proflavine, PFH, and acridine yellow, ACY, were chosen to compete with MB for the exchange sites. The MB was initially adsorbed as trimer (MB+)3and then redistributed via collisions between clay particles until equilibrium was reached. At equilibrium in the clay/MB systems, the protonated species (MBH2+) predominated at low loadings (1–5% CEC), whereas at higher loadings the trimer (MB+)3was the major species. The presence of the second, competing dye slowed the approach to equilibrium, significantly reduced the amount of MBH2+formed and provided evidence for the monomeric MB+, dimeric (MB+)2, and trimeric (MB+)3forms of MB. Moreover, the presence of PFH and ACY, which are structurally similar to MB, resulted in more dimeric character in the aggregated form of MB compared to the aggregate formed in the presence of the structurally dissimilar TFT.
Interlayer Adsorption of Macrocyclic Compounds (Crown-Ethers and Cryptands) in 2:1 Phyllosilicates: II. Structural Features
Authors: Casal B. , Aranda P. , Sanz J. , Ruiz-Hitzky E.
Published: December 2006

Intercalation of macrocyclic compounds (crown-ethers and cryptands) in 2:1 charged phyllosilicates is a topotactic reaction, the lamellar structure of the pristine material being preserved. X-ray diffraction and spectroscopic (IR, NMR) results provide information on the main structural characteristics of the intercalates. Guest species, which form 1 : 1 or 2 : 1 ligand/cation intracrystalline complexes, lie flat or tilting between the host layers as can be deduced from the increase in the basal space of the silicate and the dichroic effect observed on the CH and NH IR vibration bands of the guest species, after intercalation. The chemical shift observed in 23Na NMR spectra of the solids is associated with the different environment of the cation before and after the intercalation process.
Evidence of a Precursor in the Neoformation of Palygorskite — New Data by Analytical Electron Microscopy
Authors: Suarez M. , Martin Pozas J. M. , Robert M. , Elsass F.
Published: December 2006

The rocks of the palygorskite deposit at Bercimuel (Segovia, Spain) have been studied by transmission electron microscopy and microanalysis. These rocks correspond to the zone of convergence of two alluvial fan systems that have filled the small basin of the River Riaza and would originally have been composed of illite and quartz silts. Among the accumulations of palygorskite it is possible to observe surrounded particles of micromicas that have undergone dissolution and opening thereby giving rise to disordered illite-smectite mixed-layer clays. This process continued up to the individualization of structural relics formed of units of 1–5 layers. At the same time, the chemical composition was modified with a loss of K and Al and a relative increase in Si and Mg, progressively evolving towards the composition of palygorskite. The paleogeographic position of the deposits, and the climatic conditions (arid environment), appear to be the dominant factors in the neoformation of palygorskite by alteration of the original sediments. The basic mineralogical process could be referred to as ‘early diagenesis’ in the formation of calcretes.
Identification of pseudoboehmite in mixtures with phyllosilicates
Authors: Violante A. , Huang P. M.
Published: December 2006

The influence of kaolinite and montmorillonite on the identification of pseudoboehmite was studied by X-ray diffraction (XRD), differential thermal analysis (DTA), infrared absorption (IR), and transmission electron microscopy (TEM). In the randomly oriented samples containing different proportions of the clay minerals and pseudoboehmite, pseudoboehmite was not easily detectable by XRD even in a sample containing 40% of pseudoboehmite. Preheating of the samples at 110-300°C improved the detection limit to 30%. In samples obtained by mixing suitable amounts of the suspensions of the clay minerals (<2μm)and pseudoboehmite, the identification of pseudoboehmite was even more difficult. In oriented samples, pseudoboehmite was detectable only when present in amounts >30%, at low full-scale counts per second (1000-400 cps), on preheated samples in the presence of kaolinite, or on the samples that were Mg-saturated and solvated with ethylene glycol in the presence of montmorillonite. Identification of pseudoboehmite in the presence of kaolinite or montmorillonite by DTA, IR or TEM failed, even in samples containing 50% pseudoboehmite. In the presence of both kaolinite and montmorillonite (1:1 w/w), the identification of pseudoboehmite became much more difficult than in the presence of either mineral alone. The presence of pseudoboehmite in soils may, thus, be undetectable by standard clay mineralogical analyses.
Ammonium illite from anchimetamorphic shales associated with anthracite in the Zemplinicum of the western Carpathians
Authors: Šucha V. , Kraus I. , Madejová J.
Published: December 2006

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.
Analysis of permeability controls: a new approach
Authors: Cade C. A. , Evans I. J. , Bryant S. L.
Published: December 2006

By modelling a range of rock-forming processes such as compaction and various styles of cementation, a new understanding of how they affect pore-system geometry, and hence permeability, has been gained. For example, almost identical permeability-porosity trends result from progressive compaction or grain overgrowth cementation in a clean sandstone, and these trends are curvilinear on the traditional log-linear plot. The steepening which defines the curve marks the onset of pore-throat blocking. Other cement styles, such as pore-filling carbonates or grain-rimming clays, show different porosity-permeability trends. This new understanding can be used predictively (predicting permeability from predictions of grain size and diagenetic style), or as a tool for identifying the important permeability controls in a set of field data. This latter application is presented and illustrated using data from a variety of sandstone types. This approach has important advantages over commonly used multivariate statistical analysis approaches. It can quickly provide a good understanding of what are (and are not) the important controls on permeability. It also provides a basis for more focused and meaningful statistical analysis to quantify these controls.
Ammonium fixation during illite-smectite diagenesis in Upper Jurassic shale, North Sea
Authors: Lindgreen H.
Published: December 2006

Claystones of Kimmeridgian-Volgian-Ryazanian age are the main source rock for oil in the Central Trough, North Sea. During oil generation, illite layers form in illite-smectite (I-S) and the illitesmectites become short-range (IS) ordered and eventually long-range (ISII) ordered. The formation of illite layers involves dehydration and fixation of interlayer cations, K+ and NH4+. The content of soluble NH4 and K in core samples and the content of NH4 and K in I-S were determined, the NH4 by an isotope dilution method. In the Central Trough, soluble K+ decreases with depth, whereas soluble NH4+ increases with depth. From ∼3 km, the ratio NH4/K increases with depth, to an average of ∼0.5 at 4.4 km. In I-S, the ratio NH4/K shows a similar increase with depth. The NH4/K ratio increases significantly in I-S during ordering. It is concluded that NH4 fixation in I-S may be of general importance during burial diagenesis of oil source rocks.
Stable isotopes in illite: the case for meteoric water flushing within the Upper Jurassic Fulmar Formation sandstones, UK North Sea
Authors: Wilkinson M. , Fallick A. E. , Keaney G. M. J. , Haszeldine R. S. , McHardy W. J.
Published: December 2006

The extent to which the diagenesis of sedimentary sequences within the UK North Sea is influenced by the passage of meteoric water is subject of current debate. Petrographic (SEM, TEM, thinsection) observation and stable isotope ratios from authigenic illite separates are used to deduce the pore-fluid evolution of the Fulmar Formation within well 29/10-2 from the Central Graben, with emphasis on the past importance of meteoric water flushing.

Petrographic observation shows the illite to have two modes of occurrence (pore-filling and as pseudomorphs after feldspar). These can be equated with two authigenic crystal morphologies (plates and laths) observed by TEM within illite separates prepared for isotopic analysis. The laths are equated with late stage ‘hairy’ pore-filling illite, the plates with illite pseudomorphs after feldspar which are difficult to date petrographically.

The δD (−55 to −87‰ SMOW) and δ18O (12.4–14.6‰ SMOW) analyses can be interpreted in terms of a conventional hydrogen-oxygen cross-plot to indicate illite precipitation from pore-waters of meteoric origin at 50–60°C. However, these predicted precipitation temperatures are irreconcilable with the observed petrographic sequence. The hydrogen isotope compositions may have undergone resetting during burial. Consequently, only the δ18O data may be confidently interpreted in terms of the conditions of illite precipitation. This implies illite growth at temperatures above 80°C from waters with δ18O between −2.5 and +6‰ SMOW, leaving the case for meteoric water flushing of the sandstones unproven.
Smectite to illite conversion and K-Ar ages
Authors: Velde B. , Renac C.
Published: December 2006

Interpretation of K-Ar determinations of the apparent age of crystallization of diagenetic potassic layer silicates should take into account the current ideas concerning the smectite to illite conversion of clay minerals. These minerals are the major K-bearing neogenic phases in sedimentary rocks and, therefore, it is important to keep in mind their origin and the pathway of their evolution. Another important contributor to K and Ar content are detrital minerals which are not considered in detail in this paper. The radiogenic Ar retained by diagenetic illitic clay minerals (illite and illite-smectite interstratified minerals with a low smectite content) will be a function of: (1) the amount Ar lost through the destruction of mixed-layer and small grained illitic material dissolved to produce new, larger, illite-rich crystals; and (2) the amount of Ar produced and retained in the growing, stable illite mineral grains. Hence the K/Ar ratios in diagenetic illites depend on several variables. In samples where the detrital contribution is small, when the illite growth reaction is rapid, i. e. occurring over a short period of time, the accumulated radiogenic Ar can be used to date the geologic event which caused this crystal growth. However, if the process occurs over a significant period of time, as is usually the case in shales, the age deduced by radiogenic Ar content will indicate the changes in mineralogy and grain-sizes of the different participating phases. These changes will be the result of time and temperature variables of the sedimentation and burial of the samples studied. The radiogenic Ar accumulated will reflect a sequence of mineral changes over a period of time.
The thermal behaviour of an Fe-rich illite
Authors: Murad E. , Wagner U.
Published: December 2006

The phase changes that took place upon heating an Fe-rich illite (OECD #5) to 1300°C in an oxidizing atmosphere were studied by a variety of mineralogical techniques. Infrared spectra, showing the stepwise dehydroxylation of the illite, showed good agreement with variations in sample colour and Mössbauer spectra. Dehydroxylation did not lead to noticeable variations in X-ray powder diffraction patterns until the structural breakdown of illite and formation of new phases at about 900°C Mössbauer spectroscopy proved to be very sensitive to all changes induced by heating, showing the disappearance of Fe2+ at 250°C, the gradual dehydroxylation between about 350 and 900°C, and characteristic features of the products formed at higher temperatures, e.g. the formation of hematite as the illite structure breaks down and the subsequent disappearance of hematite due to the incorporation of Fe in glass above 1200°C. The formation of hematite in clusters large enough to order magnetically at room temperature was first observed in the sample heated to 900°C, whereas at 4.2 K, significant proportions of a magnetically ordered phase could already be identified in the sample heated to 650°C.
Local ordering of chromium(III) in trioctahedral hydroxide sheets of stichtite studied by ion exchange chromatography
Authors: Hansen H. C. B. , Bender Koch C.
Published: December 2006

Stichtite is the layered Mg-Cr(III) hydroxide carbonate of the pyroaurite group. The possibility of describing Cr(III) short range order (SRO) in stichtite by use of ion chromatography of the Cr(III)-hydroxo species following acid dissolution of the compound is described. Two synthetic stichtites of similar composition (average Mg5.73Cr(III)2.27(OH)15.93(O)0.07(CO3)1.10·xH2O) prepared in the absence or presence of hydroxy-bridged Cr(III) dimers and a sample from Dundas, Tasmania, Mg6.29Ni(II)0.02Cr(III)0.90Al0.65Fe(III)0.15(OH)15.26(OH2)0.74(CO3)1.23·xH2O have been examined. Ion chromatography showed the highest degree of SRO for the Dundas stichtite. For the synthetic stichtites the sample synthesized from Cr(III) dimers had the highest SRO. No information on cation ordering could be extracted from powder X-ray diffraction data. Visible spectroscopy indicates that for constant Mg:Cr(III) ratio the crystal field splitting increases with increasing SRO. Two different OH-stretching IR absorption bands (3585 and 3472 cm−1) are assigned to OH coordinated to 3Mg and OH coordinated to 2MgCr or Mg2Cr, respectively.
Kinetics of phosphate sorption and desorption by synthetic aluminous goethite before and after thermal transformation to hematite
Authors: Ruan H. D. , Gilkes R. J.
Published: December 2006

Goethite is an important component of many soils and its transformation to hematite by fire may affect phosphate retention. This study deals with the kinetics of phosphate sorption and desorption by synthetic aluminous goethites and their dehydroxylated products. Phosphate sorption and subsequent desorption were measured for periods up to 128 h. Phosphate sorption increased with equilibrium solution concentration, Al substitution and surface area, and decreased with increasing crystal size. The trend in amount of phosphate sorbed was: partially dehydroxylated goethite > hematite > goethite. Sorption and desorption kinetics are well described by the modified Elovich equation. Desorption of a minor proportion of the sorbed P was rapid and this was sometimes followed by minor resorption. The amount of P desorbed directly reflected the amount that was initially sorbed. Acid dissolution of the Fe oxides with sorbed phosphate suggested that most phosphate was present at the crystal surface and not in relatively poorly accessible micropores.
Electro-fluorescence studies of the binding of fluorescent dyes to sepiolite
Authors: Windsor S. A. , Harrison N. J. , Tinker M. H.
Published: December 2006

Aqueous suspensions of sepiolite, tagged with fluorescent dyes, have been studied using electro-fluorescence polarization spectroscopy. The binding modes of some 37 fluorescent dyes and optical brightening agents to the rod-like sepiolite particles have been determined. Many of the dyes are found to bind with a degree of order to the clay particle's major axis. The binding geometries of the cationic dye molecules tested were found to be dependent upon molecular size. This supports the view that these cationic dye molecules are constrained within the channels which are characteristic of the mineral sepiolite. Results for uncharged and anionic dye molecules are also presented; no dependence of binding geometry upon molecular size was found. The anionic molecules are most likely to associate with the exterior cationic magnesium surface. The results indicate that some of the anionic dyes are too large to fit in the channels. Some of the uncharged molecules adopt a number of orientations upon binding which gives rise to an average geometry being observed for these dyes.
Fine-grained laminated Quaternary sediments in the Ebro Valley (Spain): characteristics and formation
Authors: Garcia-Gonzalez M. T. , Wierzchos J. , Vizcayno C. , Rodriguez R.
Published: December 2006

Fine-grained sediments are a major parent material in Ebro Valley soils. During the 1960s, the area was transformed by irrigation and soils underwent serious degradation processes. The sediments have a fine texture, high CaCO3contents and high salinity-sodicity levels, and contain illite as the most important phyllosilicate in the fine fractions. Two groups of finely laminated organization have been recognized in terms of layer thickness and grain-size distribution. Based on texture, the microstructure of the silty and clayey layers is different, irrespective of their mode of formation; porosity characteristics also differ between layers, leading exclusively to a capillary evaporation flow that results in salinization of the plough horizons. The sediments are formed by two different mechanisms, each layer resulting from uninterrupted sedimentation of a suspension or from deposition of suspended particles by water discharge.
Clay minerals as records of temperature conditions and duration of thermal anomalies in the Paris Basin, France: discussion
Authors: Spötl C. , Worden R. H. , Walgenwitz F.
Published: December 2006

A highly illitic phase containing <5–10% interstratified smectite was described by Mossmann et al. (1992) and, more recently, by Clauer et al. (1995) from Upper Triassic sandstones of the Paris Basin (France). This phase is present in all size-fractions of all samples and was interpreted as authigenic. The K/Ar model ages of this illite range from 189–200 Ma and, combined with oxygen isotope data, were cited as evidence of high-temperature (220–250°C hydrothermal precipitation from highly 18O-enriched fluids at burial depths of only 500 m.

We suggest that this type of illite is more likely to be diagenetically altered detrital illitic material and unlike authigenic illite-smectite which is also present in many of their samples. This reassessment of their petrographic observations leads to a much more realistic diagenetic interpretation consistent with previous studies of the basin and avoids the need to invoke basin-wide hydrothermal activity during shallow burial.
Clay minerals as records of temperature conditions and duration of thermal anomalies in the Paris Basin, France: a reply to the discussion by Spötl et al.
Authors: Clauer N. , O'Neil J. R. , Furlan S. , Mossmann J. R.
Published: December 2006

Spötl et al. (1996) have re-examined studies published by us on clay materials of sandstones in the Paris Basin. They refute the XRD characterization, K-Ar dating and formation temperature of one of the interstratified illite-smectite phases identified and have provided an alternative explanation of the published results. However, the authors ignored some basic data provided in the publications under discussion, and they have not been able to explain readily why some of the data were discarded. Furthermore, part of their disagreement is unsubstantiated. We maintain that, on the basis of coherency and consistency of all the data obtained, as well as on independent published results, the most satisfactory interpretation for the thermal evolution of the Paris Basin is the one that we suggested in our publications.
Stability of sepiolite in neutral and alkaline media at room temperature
Authors: Martinez-Ramirez S. , Puertas F. , Blanco-Varela M. T.
Published: December 2006

The chemical and structural stability of a Spanish sepiolite from Vallecas, Spain, was studied in 0.04 n NaOH (pH = 12.6), a saturated solution of Ca(OH)2 (pH = 12.6) and deionized/distilled water (pH = 7). The chemical stability was evaluated by determining the concentrations of Mg, Si and Ca in the solid residues during the kinetic test. The structural stability was studied by determining the changes in specific surface area and ‘crystallite’ size. The specific surface was determined by the BET method and the ‘crystallite’ size by the profile of the X-ray diffraction line. The main conclusion was that sepiolite is a material with high chemical stability in neutral and alkaline media, with no significant structural changes. However, in alkaline media, greater dissolution of silica was observed than in neutral media, the silica being derived from the most external tetrahedra attached to the OH− groups.
Preparation and infrared spectroscopic characterization of reduced-charge montmorillonite with various Li contents
Authors: Madejová J. , Bujdák J. , Gates W. P. , Komadel P.
Published: December 2006

A series of reduced-charge montmorillonites (RCMs) was prepared from Li-montmorillonite from Jelšový Potok (Slovakia) by heating at various temperatures (105–210°C for 24 h. The amount of fixed Li, 0.09–0.67 per O20(OH)4, increased with increasing temperature, confirming preparation of a set of samples of variable layer charge from the same parent Li-montmorillonite by varying only the preparation temperature. Infrared spectroscopy revealed that Li was trapped in the hexagonal cavities of the tetrahedral sheet at all temperatures. Partial deprotonation of the samples, reflected in the decrease of the intensities of the OH-bending bands, was observed after treatments above 120°C. Analysis of the OH-stretching region showed Li in the previously vacant octahedra in the samples heated above 150°C. Weak inflections near 660 and 720 cm−1 confirmed development of local trioctahedral character of octahedral cations coordinated with OH groups in the sample heated at 210°C. Gradual decrease of the layer charge due to Li fixation led to a shift of the Si-O stretching band to higher frequencies and to the appearance of new, pyrophyllite-like bands at 1120 and 419 cm−1.
The formation of ice between hydrotalcite particles measured by thermoporometry
Authors: Titulaer M. K. , Talsma H. , Jansen J. B. H. , Geus J. W.
Published: December 2006

Thermoporometry (TPM) was applied to hydrotalcite precipitates prepared with carbonate, bicarboxylic acids and chloride. It was used to measure the formation of an ice body between the hydrotalcite particles. Before TPM could be applied, the dried hydrotalcite precipitate had to be soaked for two weeks in water. The mean value of a factor F measured by TPM, which described the shape of the ice body in hydrotalcite, was 1.7. This value was between those of a purely cylindrical (F = 2) and a purely spherical ice body (F = 1), indicating the formation of ice lenses. From the radius of the ice body, Rn, ice volume, Vn and shape factor F, the corresponding specific surface area of the hydrotalcite particles could be assessed. The TPM indicated that the distance between the separate hydrotalcite crystals in water, which is equal to 2(Rn+0.9) nm, was a function of the type of anion incorporated at the interlayer, such as chloride and bicarboxylic acid. The pore volume and surface area of the hydrotalcite particles measured by TPM were compared with those determined by the traditional nitrogen sorption technique on dried hydrotalcite. It appeared that sorption of N2 yielded much lower values than TPM. This difference was interpreted as being due to slow penetration of N2 through the dried hydrotalcite samples to the interparticle voids.
Surface fractal dimensions of synthetic clay-hydrous iron oxide associations from nitrogen adsorption isotherms and mercury porosimetry
Authors: Cells R. , Cornejo J. , Hermosin M. C.
Published: December 2006

Model associations of layer silicates (kaolinite and montmorillonite) and iron oxyhydroxides were obtained by precipitating hydrous iron oxide in clay suspensions at different loading. The porosity of these clay-hydrous iron oxide associations was studied in the macro- and mesopore range by mercury intrusion porosimetry (MIP) and in the micropore region by nitrogen adsorption isotherms, being the fractal geometry applied to the approaches used in porosity studies. Results of nitrogen adsorption isotherms showed that surface area and microporosity of kaolinite and montmorillonite increased upon Fe precipitation, especially for montmorillonite. This process is accompanied by an increase in the surface fractal dimension Ds(N2) by the presence of hydrous iron oxide coating the clay particles. Results of MIP also showed a decrease in the pore volume by Fe precipitation on montmorillonite due to a decrease in the number of large pores and a development of new medium-size pores. An increase of the fractal dimension Ds(Hg) was also observed.
Geochemistry and mineralogy as indicators of parental affinity for Cenozoic bentonites: a case study from S. Croce di Magliano (southern Apennines, Italy)
Authors: Laviano R. , Mongelli G.
Published: December 2006

The major and trace element contents and mineralogical composition of Cenozoic bentonites from the southern Apennines (Italy) have been determined, for the whole-rocks and the <2 µm size-fractions, in order to constrain parental affinities. The main mineralogical and chemical differences have been recognized in eleven samples allowing them to be grouped into two distinct subsets. The differences are based on smectite abundance, occurrence or lack of detrital clay phases, different contents of Ti, Fe, Mn, K, P, Rb, Sc, V, Cr and Ni and differences in the Eu/Eu* and Ti/Al elemental ratios. These ratios indicate an affinity for felsic volcanics for the subset showing high smectite contents. The low smectite subset shows, instead, an affinity for Cretaceous-Oligocene southern Apennine shales. A similar result is obtained using the La-Th-Sc and Th-Sc-Zr/10 diagrams. We suggest that during the deposition of the southern Apennine shales, episodic volcanic events took place. These were associated with the suture stage of the Tethyan ocean that promoted accumulation of felsic ash in the related basin and the diagenetic alteration of these materials produced bentonitic layers interbedded with shales.
Effects of ground granulated blast furnace slag (GGBS) on the strength and swelling properties of lime-stabilized kaolinite in the presence of sulphates
Authors: Wild S. , Kinuthia J. M. , Robinson R. B. , Humphreys I.
Published: December 2006

The use of ground granulated blast furnace slag (ggbs) is well established in many cement applications where it provides enhanced durability, including high resistance to chloride penetration, resistance to sulphate attack and protection against alkali silica reaction (ASR). The use of ggbs in soil stabilization is, however, still a novel process in the UK although it has been used in South Africa. This paper reports on efforts to extend the use of ggbs to highway and other foundation layers by determining the beneficial effect which it has on the reduction of expansion due to the presence of sulphates. The paper describes the results of laboratory tests on lime-stabilized kaolinite containing different levels of added sulphate to which different amounts of ggbs have been added. The tests determine the strength development of compacted cylinders, moist cured in a humid environment at 30°C, and the linear expansion of these moist cured cylinders on soaking in water. The results illustrate that small additions of ggbs to sulphate containing clays which are stabilized with lime reduce substantially their expansion when exposed to water and have no significant deleterious effect on strength development.
Aluminium influence on iron oxides: XVIII. The effect of Al substitution and crystal size on magnetic hyperfine fields of natural goethites
Authors: Friedl J. , Schwertmann U.
Published: December 2006

Two sets of natural Al-substituted goethites from contrasting surface environments (24 tropical and subtropical soils vs. ten lake iron ores from Finland) were characterized by Mössbauer spectra obtained at room temperature and 4.2 K. A negative correlation between Bhf and Al substitution (R2 = 0.751) was found by combining the data of all the samples, which was slightly improved (R2 = 0.779) by taking the mean coherence length perpendicular to 111 (MCL111) into account. The effect of Al on lowering Bhf was, however, stronger for the tropical soil goethites than for those of the lake ores. This is parallelled by a corresponding difference in the unit-cell decrease per unit Al substitution. These differences are believed to result from the crystallization conditions in the two different environments.
Properties of synthetic goethites with Co for Fe substitution
Authors: Gasser U. G. , Jeanroy E. , Mustin C. , Barres O. , Nüesch R. , Berthelin J. , Herbillon A. J.
Published: December 2006

Isomorphic substitution in goethites is common in nature and the properties of goethites generally change as a function of the degree of substitution (e.g. Al-goethites). In synthetic goethites, substitution by other elements such as Co is also known. Recent literature indicates that the influence of Al and Co on the unit-cell dimensions of goethite is similar. In contrast to Al-goethites, however, little is known about other properties of Co-goethites and in this study some properties of synthetic Co-goethites were investigated by XRD, IR, TEM, TGA and reductive dissolution techniques. Eight goethite samples (S1 to S8) with varying Co concentrations were synthesized from mixed alkaline solutions of Fe(III) nitrate and Co(II) nitrate, aged at 63°C and ambient pressure. The goethites contained up to 9.5 mol.% Co. Their redness increased with Co concentration, e.g. 0.5 Y 6.0/6.4 for S1 and 6.4 YR 3.3/3.2 for S8. Surface area ranged from 46 to 88 m2/g. Unit-cell parameters a, b, c and v all showed a negative linear dependency on the Co concentration of the goethites. Transmission and diffuse reflectance IR spectrometry showed the presence of strong bands which were interpreted as v-OH, δ-OH and γ-OH vibrations. The δ-OH and γ-OH band positions showed a positive linear dependency on the Co concentration of the samples. Dehydroxylation occurred between 280 and 315°C and dehydroxylation peak positions tended to decrease with increasing Co concentrations. As with Al-goethites, Co-goethite reductive dissolution rates decreased parabolically with increasing substitution. X-ray diffraction and IR analyses, TGA and congruent reductive dissolution suggest the existence of single phases, i.e. Co-goethites of varying degrees of isomorphic substitution.