bluuebunny/crossref_metadata_2025_split huggingface dataset:
A study of organo-hectorite clay crystallization
Authors: Carrado K. A. , Thiyagarajan P. , Song K. 
Published: December 2006

AbstractA method has been developed to synthesize organo-hectorite clays directly from a Mg-silicate gel containing organic or organometallic molecules that are expected to be incorporated within the interlayer space. Complete crystallization occurs upon aqueous reflux for 48 h. The progress of clay layer formation was monitored by X-ray powder diffraction (XRD), differential thermal gravimetry (DTG), and infrared (IR) spectroscopy. Evidence of clay XRD peaks occurs after just 4 h of hydrothermal treatment, and Mg(OH)2 is no longer observable after 14 h. Observable changes in DTG and IR occur at about this time as well. Warren line-shape analysis of the 110 reflection indicates that when growth is complete the clay lamellae are on average ∼50% and 25% of the size of natural hectorites and montmorillonites, respectively. The N2 BET surface areas for all materials are also compared. Small angle neutron scattering shows that addition of tetraethyl ammonium (TEA) ions does not alter the structural integrity over that of the purely inorganic form of Li-hectorite, but that use of a cationic polymer does significantly alter the microstructure. The effect of temperature is critical, for at room temperature only the layered Mg hydroxide mineral brucite crystallizes unless very long time scales are used. The crystallizations carried out at room temperature show that clay will form after about 3 months, but that the presence of organics (at least TEA) acts to hinder this process greatly. The role of the organic molecules on silicate clay layer formation is compared with the role of organics in zeolite synthesis.
The structure of the kaolinite minerals — a FT-Raman study
Authors: Frost R. L. 
Published: December 2006

AbstractThe Fourier transform Raman spectra of the kaolinite minerals have been measured in the 50–3800 cm−1 region using near infrared spectroscopy. Kaolinites are characterized by remarkably intense bands in the 120–145 cm−1 region. These bands, attributed to the O-Si-O and O-Al-O symmetric bending modes, are both polymorph and orientation dependent. The 200–1200 cm−1 spectral range is a finger-print region for clay minerals and each kaolinite clay has its own characteristic spectrum. The structure of clays is fundamentally determined by the position of hydroxyl groups. Fourier-transform Raman spectroscopy readily enables the hydroxyl stretching region to be examined allowing identification of the component bands. The advantages of FT-Raman spectroscopy are shown to enhance the study of the kaolinite structure.
Surface microtopography of rectorite (allevardite) from Allevard, France
Authors: Kitagawa R. 
Published: December 2006

AbstractBy means of transmission electron microscopy (TEM) and the gold decoration technique, the surface microtopography of rectorite (allevardite) crystals collected from Allevard, France was investigated. On the crystal surfaces, gold decoration successfully revealed growth steps of ∼20 Å in height. Only closed polygonal steps 20 Å high occur on the 001 surface of a thick platy crystal, although spiral growth patterns were not observed. Thick platy particles were easily split into thinner plates 20 Å thick in distilled water by means of ultrasonic vibration. No step patterns were observed on the surfaces of these thin plates which correspond to the cleavage plane. The growth of this rectorite, therefore, seems to be controlled by a layer nucleation mechanism.
Interaction of montmorillonite with binuclear hydroxo-bridged iron complexes and their peroxo adducts
Authors: Weiss A. , Dick S. 
Published: December 2006

AbstractThe interaction of the cationic hydroxo-bridged binuclear iron(III) complexes of the sevendentate ligands HPTP and HPTB with montmorillonite was studied. Both complexes can be introduced reversibly into the interlayer region of the smectite. The catalase active HPTP-complex preserves its activity in the smectite interlayers. The unstable peroxide adducts of both complexes can be introduced into montmorillonite interlayers from water/H2O2 at 273 K and can be stored there for months at 243 K. Adduct/montmorillonite compounds can also be prepared by direct reaction of H2O2 with the complexes already bound to montmorillonite. From IR spectra of the adduct/montmorillonite compounds it can be concluded that the adduct of the HPTP complex contains nitrate whereas the adduct of the HPTB complex does not. These results can help to decide whether structures of the adducts proposed in the literature are possible or not and may therefore open a new field of application of clay minerals in studies on unstable intermediates.
K-Ar dating of illite fundamental particles separated from illite-smectite
Authors: Clauer N. , Środoń J. , Francu J. , Šucha V. 
Published: December 2006

AbstractFundamental particles of illite-smectite from bentonites were separated into classes by high-speed centrifugation after infinite osmotic swelling of mixed-layer crystals, achieved by Na-exchange and dispersion in distilled water. In samples free of detrital contamination, the thinnest fundamental particles yield older K-Ar ages than the thicker fundamental particles. This implies that they do not preferentially lose radiogenic 40Ar due to size, and that the illitization process is a crystal growth mechanism (not nucleation plus growth). As a result, any K-Ar age of fundamental illite particles from bentonites is an integral over longer or shorter periods of time, depending on the thermal history of the rocks. In thick bentonite beds, the measured age difference between the beginning of the illitization process at the contact with the host rocks and the end in the centre of the bed records extremely slow K diffusion in these well compacted rocks. These data explain why measured K-Ar ages of illite-smectite from bentonites are younger than the corresponding age of shale illitization, inferred from the burial history of the basin. The finest technically separable size-fractions of associated shales (<0.02 μm) yield K-Ar dates* greater than the stratigraphic age. This observation points to incomplete recrystallization of detrital illite during burial diagenesis.
A vein occurrence of co-existing talc, saponite, and corrensite, Builth Wells, Wales
Authors: Garvie L. A. J. , Metcalfe R. 
Published: December 2006

AbstractUnique phyllosilicate assemblages occur in quartz-calcite veins cutting altered andesite at Builth Wells, UK. These veins show: (1) a central talc-dominated assemblage, grading into a saponite/corrensite/chlorite-dominated assemblage near their walls; (2) talc replacing calcite and quartz; and (3) closely associated blocky and fibrous saponite. Fibrous saponite occurs in narrow (<1 cm) fractures that extend for up to 1 m from major (⩽ 50 cm wide) talc-bearing veins. A thin halo (<5 mm) of wall-rock alteration, containing blocky saponite and minor corrensite, borders the fibrous saponite. These minerals may have originated when cooling, low-pH, quartz-saturated, Mg-rich fluid invaded pre-existing quartz/calcite veins. Quartz is replaced by talc where calcite dissolution caused the pH to increase. Wallrock alteration liberated Fe and Al to the fluid causing blocky saponite and corrensite to form. Fibrous saponite formed where lithostatic pressures were directed across hydraulic fractures.
Clay transformations following a leaching experiment on an acid brown soil
Authors: Turpault M.-P. , Ponette Q. , Belkacem S. , Nys C. 
Published: December 2006

AbstractThe chemical and mineralogical properties of the A1 and B horizons of an acid brown soil (typic Dystrochrept) were compared before and after a 20 month column leaching experiment. At the end of the leaching period, the organic carbon content of the A1 horizon had decreased by ∼20% compared with the original horizon. In the leached A1 horizon, the vermiculite layers of both the vermiculite and interstratified minerals were transformed into high-charge expanding layers, with the charge mainly located in the octahedral sheet. The inhibition of expansion properties by pretreatment with dithionite-citrate-bicarbonate (DCB) was explained by an increase in total layer charge induced by Fe reduction. In the B horizon, leaching resulted in a loss of sesquioxide materials, especially in the interlayers of vermiculites. In both horizons, the amounts of Al extracted by Na citrate and the amounts of Fe extracted by DCB decreased. Analysis of solution composition showed that Al mobilization was closely associated with NO3− leaching.
Interaction of aminotriazole with montmorillonite and Mg-vermiculite at pH 4
Authors: Morillo E. , Perez-Rodriguez J. L. , Rodriguez-Rubio P. , Maqueda C. 
Published: December 2006

AbstractThe interaction of aminotriazole (AMT) at pH 4 on Wyoming montmorillonite (mainly with Na ions) and Mg-vermiculite has been studied by X-ray diffraction and infrared spectroscopy. The AMT is adsorbed on montmorillonite in the cationic form by cation exchange. The amount of pesticide adsorbed was 71 mEq/100 g, which comprises ∼91% of the CEC of this sample (78.2 mEq/100 g). Saturation was reached in 24 h, giving rise to a complex with basal spacing 12.5 Å. Vermiculite adsorbs 167 mEq/100 g, almost 20% greater than the CEC (141 mEq/100 g), and the basal spacing was stabilized at 13.68 Å after five weeks of treatment with AMT. A part of the AMT is adsorbed in cationic form, displacing a great part of the exchangeable Mg2+ cations. The rest is adsorbed in molecular form by coordination to the Mg2+ cations which remain in the interlamellar space, removing a great amount of water, and remaining in the interlamellar space of vermiculite after washing with water, probably because of a steric hindrance from the AMT cations adsorbed.
Study of the humic-like compounds formed from L-tyrosine on homoionic clays
Authors: Bosetto M. , Arfaioli P. , Pantani O. L. , Ristori G. G. 
Published: December 2006

AbstractThe ability to produce humic-like polymeric compounds, with L-tyrosine as the starting material, was evaluated using different mineral systems, e.g. on Ca-, A1- and Cu(II)-saturated montmorillonite, nontronite and kaolinite, and on quartz. Clay minerals proved to be effective in the formation of these compounds, but not quartz, except in the presence of Cu(II). The newly formed compounds were fractionated by alkaline extraction. With clay systems, the amounts of substances produced appear to be related more to the interlayer cation than to the clay type. Copper cations appear to be more effective when not associated with the clay structure.
Clay- and zeolite-bearing Triassic sediments at Kaka Point, New Zealand: evidence of microbially influenced mineral formation from earliest diagenesis into the lowest grade of metamorphism
Authors: Jeans C. V. , Fallick A. E. , Fisher M. J. , Merriman R. J. , Corfield R. M. , Manighetti B. 
Published: December 2006

AbstractThe distribution, mineralogy, petrology and bulk and stable isotope chemistry of altered volcanic ash beds in the marine sediments of Mid-Triassic age (Etalian) at Kaka Point, New Zealand, are described and related to lithofacies and the geological processes controlling their development.Three varieties of altered ash occur in the Kaka Point sediments — porcellanite, claystone (bentonite) and albite-rich. Porcellanites are quartz-rich and may contain analcime and heulandite: they are restricted mainly to the on-shore facies. Claystones are rich in smectitic clay minerals and occur in both the on-shore and off-shore facies. They often contain diagenetic nodules of analcime, quartz, apatite and carbonates. The authigenic carbonates of the on-shore facies are variable in composition (sideritic, rhodochrositic, calcitic), whereas in the off-shore facies they consist only of calcite. The albite-rich lithology is very rare and is known only from the off-shore facies.The development of the porcellanite and albite-rich lithologies was restricted to slowly deposited, relatively coarse-grained ash sediments in which extensive interchange took place between the sediment's pore-waters and ambient seawater, resulting in enhanced microbial activity and high pH throughout the pore-waters of the suboxic zone beneath the water-sediment interface. The high pH increased the rate of volcanic ash hydrolysis and provided the conditions necessary for the precipitation of zeolite, feldspar and quartz. The development of smectitic claystones was associated with more rapid deposition and limited interchange between the pore-waters of the parent ash and ambient seawater. The pore-water alkalinity was generally lower and enhanced microbial activity and high pHs were restricted to patches of sediment at which quartz, analcime, apatite and carbonates formed diagenetic nodules. Modelling of the stable isotopes of the smectitic clays (δ18O, δD) and diagenetic carbonates (δ18O, δ13C) suggest that: (1) ash argillization in the on-shore facies took place in brackish water (∼25% meteoric water) at an average temperature of ∼50°C and in the off-shore facies in marine pore-waters (∼10% meteoric waters) at ∼40°C and (2) diagenetic carbonate precipitation in the near-shore facies took place at ∼30°C and in the off-shore facies at 60–80°C.The pattern of ash alteration in the marine Triassic sediments at Kaka Point is considered to represent an early stage in the development of the zeolite pattern associated with the classic area of zeolite facies metamorphism in the Taringatura and Hokonui Hills.
Palaeoweathering in slates from the Iberian Hercynian Massif (Spain): investigation by TEM of clay mineral signatures
Authors: Vicente M. A. , Elsass F. , Molina E. , Robert M. 
Published: December 2006

AbstractPalaeoweathering profiles are widely represented in the Iberian meseta. Transmission electron microscopy (TEM) and analytical electron microscopy (AEM) were used to describe the mechanisms governing the processes involved in the formation of one of these weathering profiles developed over slates of the Iberian Hercynian Massif. Three well-differentiated weathering stages were distinguished, based upon well-defined mineralogical signatures characteristic of primary or secondary minerals. The lower stage is characterized by fresh green slates composed of Fe-chlorite, micas, quartz and feldspars. The soft slates represent an intermediate weathering stage. A confined environment has permitted the development of smectite from the different primary phyllosilicates, both by neoformation of montmorillonite and transformation into beidellite. In the upper part of the profile, the red slates are the most weathered. A tropical or subtropical climate has resulted in the formation of kaolinite and abundant iron oxides over several metres. The present study demonstrates that the three identified weathering stages were formed under the same climatic conditions. Such ‘toposequences’ are developed at the present time in tropical areas (Bocquier, 1971).
Green ferric clay in non-marine sandstones of the Rewan Group, southern Bowen Basin, Eastern Australia
Authors: Baker J. C. 
Published: December 2006

AbstractAccessory green ferric clay occurs in fluvial litharenites of the Early Triassic Rewan Group. Although resembling glauconitic minerals in thin-section, electron microprobe analyses indicate that the green ferric clay is mainly ferric illite. The ferric illite may have formed in a small hypersaline lake or well drained, flood-plain soil, and its presence in the Rewan Group cannot be used to support a notion that the unit is partly marine influenced. Identification of the ferric illite by electron microprobe analysis shows that some green ferric clays, particularly those that resemble glauconitic minerals optically, may require precise quantitative elemental analysis before they can be used as a basis for environmental interpretation. Green ferric clay in the Rewan Group also includes detrital celadonite that most likely originated in a volcanic arc setting.
Clay minerals in recent sediments of the continental shelf and the Bay of Cádiz (SW Spain)
Authors: Gutierrez-Mas J. M. , Lopez-Galindo A. , Lopez-Aguayo F. 
Published: December 2006

AbstractThe distribution of clay minerals in recent sediments on the continental shelf and in the Bay of Cádiz has been analysed as part of a wider study of sedimentary exchange between the continent and the continental margin. The clay minerals included in the muddy sediments consist mainly of illite, kaolinite, smectite, randomly mixed-layered illite-smectite, chlorite, vermiculite and randomly mixed-layered illite-chlorite. Distribution of the minerals indicates that inheritance from the adjacent continental areas is the most important process involved.The relations between the clay minerals were established by Q-mode and R-mode factor analysis. The main clay mineral associations are: (1) illite-kaolinite, (2) smectite-random mixed-layered illitesmectite, and (3) kaolinite-random mixed-layered illite-smectite-vermiculite. The main sources of sediment supply to the continental shelf are the Guadalquivir and Guadiana rivers. Sediment from these rivers and from the rivers flowing into the Bay of Cádiz (mainly the Guadalete) is transported to the part of the shelf outside the bay by ebb-tide currents. The path of this outflow to the continental shelf, where the sediment is partially deposited, is influenced by the morphology of the coast and by hydrodynamic processes.
Contribution of multivariate geochemical analysis and mineralogical study in the characterization of sediments: the Miocene-Pliocene boundary in the Sorbas Basin (SE Spain)
Authors: Sanchez Bellon A. , Mosser Ch. , Moral Cardona J. P. , Roquin C. , Sebastian Pardo E. 
Published: December 2006

AbstractA mineralogical study and multivariant geochemical analysis have been carried out to determine the sedimentation processes and the influence of surrounding rocks on sediments. Analyses were made on the clay fraction of sediments and on bulk samples of rocks from nearby reliefs in the Sorbas Basin (SE Spain). Source rocks were identified by statistical analysis of trace elements and by comparison of the crystallographic parameters of phyllosilicates in sediments and supposed sources. Palaeoenvironmental conditions are recorded by specific elements in the clay minerals. The study of the B and Mg content and of the different types of smectites and palygorskite found in distinct areas has permitted a description of these conditions for this Basin. In this way, different types of deposition environment, showing varying degrees of confinement and influence from marine or continental water, have been distinguished.
Vanadium-doped titania-pillared montmorillonite clay as a catalyst for selective catalytic reduction of NO by ammonia
Authors: Bahranowski K. , Janas J. , Machej T. , Serwicka E. M. , Vartikian L. A. 
Published: December 2006

AbstractA series of V-doped titania-pillared clay catalysts, characterized by ICP-AES chemical analysis, X-ray diffraction, BET surface area measurement, and ESR spectroscopy, have been tested in the selective catalytic reduction of NO by NH3. An ESR analysis shows that V dopant is anchored to the titania pillars. Vanadyl species with differing degrees of in-plane V-O π-covalent bonding are produced depending on the method of sample preparation. Polymeric V species appear as the V content is increased. Catalytic performance of these systems depends on the method of preparation and on the V content. The best catalyst, converting 90-100% NO in the temperature range 523-623 K, is obtained by exchange of pillared montmorillonite with vanadyl ions, at an extent of exchange below the level where significant amounts of polymeric V species appear. The co-pillared catalyst, containing vanadyl centres characterized by a higher degree of in-plane ncovalent bonding (according to ESR), is less selective than the exchanged samples.
An extended X-ray absorption fine structure (XAFS) study of the calcium site in a model basaltic glass, Ca3Mg4Al2Si7O24
Authors: Hardwick A. , Whittaker E. J. W. , Diakun G. P. 
Published: December 2006

AbstractShort-range order in the oxygen co-ordination shell of the Ca ion in a glass of composition Ca3Mg4Al2Si7O24is investigated by analysis of the extended X-ray absorption fine structure. The estimate of disorder in the short-range oxygen co-ordination is no greater than that for crystalline samples of diopside and bytownite. An estimate of the oxygen environment of calcium in the particular glass is included.
Calcium-poor pyroxenes: phase relations in the system CaO MgO-Al2O3-SiO2
Authors: Biggar G. M. 
Published: December 2006

AbstractUsing previously published data and a few new data the compositions of protopyroxene, orthopyroxene, and pigeonite, coexisting with liquid in the system CaO-MgO-SiO2, are reviewed and shown to depend subtly on the number and nature of the coexisting phases such as forsterite, silica, other pyroxene, and liquid. Broadly, protopyroxene contains 0 to 1.0 wt. % CaO, orthopyroxene 1.4 to 2.2%, and pigeonite 3.0 to 6.5%, but pigeonite coexisting with olivine contains up to 1.5 wt. % more CaO than pigeonite coexisting with SiO2 at the same temperature.In the system CaO-MgO-Al2O3-SiO2 some new analyses and all previously published microprobe analyses of pyroxenes fall into three compositional groups, which are hereafter used to name the pyroxene irrespective of whatever description the original authors gave to their products. For these groups, the compositional subtleties depend on the number and nature of coexisting phases and these are illustrated using sketches of the solid solution polyhedron for each phase, to illustrate, in particular, the decomposition of pigeonite as temperature drops, at 1276°C when forsterite, diopside and liquid coexist, but at other temperatures when other phases coexist. The assemblage orthopyroxene, anorthite, diopside, forsterite is established as the solidus at 1244°C by X-ray diffraction and by new microprobe analyses, and not protopyroxene with anorthite, diopside, and forsterite as was previously accepted. Liquidus surfaces for forsterite and protopyroxene, forsterite and orthopyroxene, and forsterite and pigeonite, are drawn, with temperature data, and several crystallization paths demonstrate the double resorption boundaries, forsterite-protopyroxene-orthopyroxene-liquid and forsterite-orthopyroxene-pigeonite-liquid, and demonstrate crystallization of four pyroxenes, resorption of three of them, and reprecipitation of a second generation of one of them.No new data are presented for the solidus of the system CaO-MgO-SiO2, but a reinterpretation of the existing data suggests that the solvi of these alumina-free pyroxenes do not show an increase in CaO as temperature decreases. This is contrary to previous interpretations which have mingled data for alumina-bearing and alumina-free pyroxenes. The reinterpretation also favours the reaction protoenstatite + pigeonite ⇌ orthopyroxene at 1375°C and a revision of the previously accepted P-T (Schreinemaker's) net for the pyroxenes is proposed which does not accept orthopyroxene ⇌ protopyroxene + diopside at 1100°C at one bar, which previously has always been accepted by extrapolation from the experimental data at 1 kbar.