bluuebunny/crossref_metadata_2025_split huggingface dataset:
Origen de niveles continentales silicificados con alunita en el Preluteciense de Salamanca España
Authors: Saavedra J. , Sanchez Camazano M. 
Published: December 2006

ResumenLos rasgos característicos geológicos (relieve bajo o medio, clima árido-semiárido, contrastado) y mineralógicos (asociación ópalo-alunita-caolinita) de niveles continentales Prelutecienses apoyan una hipótesis genética no hidrotermal. La evaporación de aguas portadoras de sílice disuelta, procedente de una meteorización del basamento, durante una estación seca, en depresiones, conduce a una precipitación de ópalo. Por otra parte, la desecación de áreas cubiertas por vegetaciones implica una descomposición bacteriana anaeróbica de materia orgánica y génesis de sulfuros; posteriormente, la aireación oxida a estos sulfuros y se generan aguas sulfatadas ácidas. Estas se mezclan con las que contienen silice, precipitando entonces conjuntamente ópalo, alunita y, si el Al3+ está en exceso, tambien caolinita.
Activation of a sepiolite with dilute solutions of HNO3 and subsequent heat treatments: II. Determination of surface acid centres
Authors: Bonilla J. L. , Lopez-González J. de D. , Ramírez-Sáenz A. , Rodríguez-Reinoso F. , Valenzuela-Calahorro C. 
Published: December 2006

AbstractA sepiolite from Toledo, Spain, was activated with dilute solutions of HNO3 (0·25, 0·50 and 0·75 m) followed by heat treatment at 110, 200, 300, 400 and 500°C for 10 h. The retention of n-butylamine in cyclohexane solution was used to follow the variation of surface acid centres of the sepiolite as a function of the acid and heat treatments, these reaching a maximum for the product treated with 0·75 m HNO3 and heated at 300°C. Acid treatments within the range 0·50–0·75 m and subsequent heat treatment at 200–300°C for 10 h yielded products with the highest surface activity.
Variation du parametre b et de la distance basale d001 dans une Serie de saponites a charge croissante: II. Etats ‘zero couche’
Authors: Suquet H. , Malard C. , Copin E. , Pezerat H. 
Published: December 2006

ResumeHuit saponites de synthèse à charge croissante ont été étudiées à l'état ‘zéro couche’ (vide, P2O5) avec différents cations interfoliaires.On observe—avec le cation K—une croissance linéaire du paramètre b en fonction du taux de substitution Si-Al, mais cette croissance est bien plus faible que celle observée avec les mêmes minéraux hydratés à ‘deux couches’.On observe par ailleurs pour les cations K, Ba, Rb et Cs des relations linéaires entre les valeurs du paramètre b et de d001 d'une part et le rayon du cation d'autre part. Les cations plus petits (Na et Li) conduisent à des solutions structurales différentes. Avec le sodium la structure 1 M n'est plus conservée, les feuillets sont décalés les uns par rapport aux autres. Avec le lithium, le type d'empilement 1M est conservé mais c'est l'entité Li+-H2O qui est piégée dans les cavités ditrigonales placées face à face.L'ensemble de ces résultats permet de montrer que les interactions entre touche interfoliaire et feuillets sont beaucoup plus fortes dans l'état ‘zéro couche’ que dans les états hydratés à une ou deux couches d'eau. Ces interactions sont fonction du rayon des cations interfolaires et peuvent entraîner une rotation des tétraèdres, ce qui conduit à discuter de la validité des équations donnant l'angle de rotation α en fonction de la composition des phyllosilicates.
Mössbauer study of glauconites from Poland
Authors: Kotlicki A. , Szczyrba J. , Wiewióra A. 
Published: December 2006

AbstractFour bands occur in the Mössbauer spectra of pelletal glauconites ranging in age from Cambrian to Oligocene. Components due to Fe3+ in the cis M(2) positions are visible in all the spectra but their shapes depend on the expanding layer content. In the spectrum of the Oligocene glauconite a very well-developed shoulder due to Fe2+ in the trans M(1) positions is observed. In the younger glauconites (15–20% expanding layers) the conventional assignments of the spectra indicate that Fe2+ occupies the trans M(1) positions, the cis M(2) positions being vacant. Conversely, in the Palaeozoic samples (~5% expanding layers) the cis occupancy significantly prevails over trans occupancy.
Geological modelling of clay diagenesis in sandstones
Authors: Hurst Andrew , Irwin Hilary 
Published: December 2006

AbstractPorewater composition is the main control on diagenetic reactions in sandstones. Porewater has two possible contrasting primary sources: (i) fresh meteoric water, which is dilute and acidic, (ii) sea-water, which is alkaline and more concentrated than meteoric water. During burial, unstable minerals equilibrate with these porewaters, thus increasing the concentrations of dissolved species. A simple manometer model is used to describe the diagenesis of interconnected (fluvial or deltaic) sandstones. This model illustrates the following geological relationships: (a) a hydraulic head causes meteoric waters to penetrate deep into sedimentary basins, typically generating authigenic kaolinite; (b) decrease of the hydraulic head (by lowering the land level or by raising sea level) causes concentrated brines to rise within the basin, typically forming illitic cements; (c) enclosed sandstones (marine facies) are isolated from meteoric water flux and only receive fluxes when fault-induced or when uplifted. Kaolinite morphology and distribution are identified as being flux- or diffusion-controlled.
Electron microscope and X-ray diffraction studies of filamentous illitic clay from sandstones of the Magnus Field
Authors: McHardy W. J. , Wilson M. J. , Tait M. 
Published: December 2006

AbstractScanning electron microscopy revealed that the organization of the interstitial micaceous mineral in the title sandstones depended on the manner of drying of the specimen. After air- and freeze-drying, the lath-like mineral tended to occur as mats densely packed against the pore walls, whereas after critical-point drying an open tangled web of very long, thin ribbons virtually filling the pore space was observed (this arrangement is the one most likely to occurin situ). The ends of these filamentous ribbons often appear to be bedded in authigenic quartz overgrowths on sand grains, thus anchoring them firmly in the pores. From transmission electron microscope observations, the individual laths were frequently only 2–3 nm thick and, from electron diffraction patterns, elongated along the a-axis: the stacking modification is 1M. X-ray diffraction patterns are those that would be expected from a fully-ordered interstratified mica-smectite containing ∼20% smectite layers. It is difficult to reconcile this with the thickness as observed under the transmission electron microscope, but a possible explanation is that the ‘smectite’ interlayers in reality represent spaces between individual crystals which formed when they sedimented into an oriented aggregate.
Clay mineral stratigraphy in the Permo-Triassic red bed sequences of BNOC 72/10-1A, Western Approaches, and the south Devon Coast
Authors: Fisher M. J. , Jeans C. V. 
Published: December 2006

AbstractThe Permo-Triassic red bed sequence penetrated in BNOC Well 72/10-1A, located in the Western Approaches, is divided into eight clay mineral zones. The zones are defined by variations in the clay assemblage in which iron- and magnesium-rich chlorite, corrensite and mica occur. This zonal sequence is matched mineralogically and stratigraphically with the pattern of clay mineral variation recorded from the Permo-Triassic sediments of the south Devon coast, some 500 km distant.
Volcanic clays in the Cretaceous of southern England and Northern Ireland
Authors: Jeans C. V. , Merriman R. J. , Mitchell J. G. , Bland D. J. 
Published: December 2006

AbstractThe mineralogy, petrology and trace element geochemistry of volcanogenic glauconites and smectite-rich clays are described and related to clay assemblages in Lower and Upper Cretaceous sediments of southern England and Northern Ireland. Volcanogenic glauconite grains represent argillized lava particles of predominantly mafic composition and may have been derived from submarine basaltic magmatism; they occur in all the sediments examined (Aptian-Senonian), and are particularly abundant in the Cenomanian-Campanian Hibernian Greensand of Antrim. The smectite-rich clays in southern England have developed by the argillization of predominantly acid or alkaline ash during early diagenesis. Three types of volcanogenic deposit are recognized. Primary bentonites are thin ash-falls deposited in quiet, brackish and marine waters (Speeton Clay, Ryazanian; Weald Clay, Barremian). Secondary bentonites are local accumulations of ash transported into the Cretaceous seas by rivers draining ash-blanketed, local land areas (London Platform, Portsdown Axis). These deposits are well-developed in the Sandgate Beds, Folkestone Beds and their contiguous deposits, and the lower part of the Gault (Upper Aptian-Middle Albian). The ash originated from penecontemporaneous, subaerial vulcanism located in the southern part of the North Sea. The most conspicuous phase of activity occurred during late Aptian times and has been dated by 40Ar/39Ar isotope analysis at 112 m.y. Bentonitic clays and marls are widespread accumulations of argillized ash that occur as a fine-grained fringing facies to glauconitic quartz sand facies. They make up the upper part of the Atherfleld Clay (Aptian) and the upper part of the Gault (Upper Albian), and they are associated respectively with the Hythe Beds (Aptian) and the Upper Greensand (Upper Albian). They may also occur in the lower part of the Lower Chalk (Cenomanian). The distribution pattern of these smectite-rich clays in southern England is related to the changing palaeogeography of the area in Cretaceous times, and the general coincidence of extensive glaueonite deposits and smectite-rich clays in the Middle and Upper Cretaceous of western Europe and along the eastern seaboard of North America is briefly discussed.
Supergene alteration of metamorphic chlorite in an amphibolite from Massif Central, France
Authors: Proust D. 
Published: December 2006

AbstractThe mineralogical and chemical changes of sheridanite were followed in different alteration horizons as weathering of its host amphibolite increased. Microscopic and microprobe analyses of phases produced in or around the chlorite allowed a classification of the different alteration stages relative to their position in the profile. In the unweathered rock, prehnite and a sericite—kaolinite assemblage appear to have formed at grain boundaries between chlorites and plagioclases. These represent low-pressure (PH2O < 2.5 ± 1 Kb) and low-temperature (320–360°C) metamorphic phases. In the saprock, where initial rock structure is still preserved, chlorites weather to a more or less regular mixed-layer chlorite-vermiculite. In the saprolite, large-grain (20 µm) vermiculite forms in the clayey zones (plasma) when rock structure is destroyed. The chemical composition of these newly-formed minerals is influenced by the original chlorites and mixed-layer minerals.
Particle-size distribution, cation exchange capacity and charge density of deferrated montmorillonites
Authors: Stul M. S. , Van Leemput L. 
Published: December 2006

AbstractDifferent montmorillonites (Otay, Chambers, Marnia, Camp Berteau, Moosburg, Greek White, Wyoming bentonite were deferrated with a dithionite/citrate solution; iron sulphide by-products were eliminated with an HCl washing and citrates with an H2O2 oxidation. The smaller CEC after deferration could not be assigned to either (i) the occurrence of a positive correlation between CEC and particle sizes smaller than 0.2 µm or (ii) to the mean charge density of these sub-fractions. All sub-fractions had a heterogeneous interlayer cation density distribution.
An investigation of the nature and reducibility of Ni-hydroxy-montmorillonites using various methods including temperature-programmed reduction (TPR)
Authors: Ghesquiere C. , Lemaitre J. , Herbillon A. J. 
Published: December 2006

AbstractA number of Ni-hydroxy-montmorillonite complexes were prepared by titrating NiCl2solutions with NaOH in the presence of charge-reduced and normal montmorillonite suspensions. These complexes were characterized by chemical analysis, CEC, XRD, IR and temperature-programmed reduction (TPR). TheR(charge-reduced) Ni-hydroxy complexes proved to be merely mechanical mixtures of Ni(OH)2and clay. The reducibility of Ni contained in these samples was not affected by preliminary heat treatments. The nature of theN(normal) Ni-hydroxy montmorillonites depended principally on the amount of Ni actually incorporated into the precipitates. Neither the OH/Ni ratio selected for the preparation or the quantity of Ni initially added completely determined the type of complex formed. TPR patterns of theNsamples generally showed three reduction bands whose respective intensities varied with the quality and the amount of Ni present. One of these reduction bands, occurring at high temperature, measured the extent of incorporation of Ni into the silicate framework during the TPR run. The intensity of this high-temperature band with respect to lower temperature ones was increased by thermal pretreatments. The results emphasize that when TPR patterns of natural Ni-bearing clays are being interpreted it is important to recognize that thermal transformations may occur in the samples caused by the heat supplied during the TPR run itself.
Authigenic silicate minerals in phosphorites of the Negev, Southern Israel
Authors: Nathan Y. , Soudry D. 
Published: December 2006

Phosphorites occur throughout the Negev, southern Israel, within the upper part of the Mishash Formation of Late Campanian age. These phosphorites are part of the Upper Cretaceous-Eocene Tethys phosphatic province. Two units can be differentiated in the Mishash Formation: a lower chert unit and an upper phosphatic unit (Nathan et al., 1979). In the upper unit, rich, economic phosphorite beds with more than 25% P2O5 alternate with chert beds and so-called ‘sterile intercalations’ which contain about 15% P2O5.Clinoptilohte (Mumpton, 1960), a zeolite of the heulandite-clinoptilolite family, was identified from XRD patterns of air-dried and heated samples of the clay fraction from the insoluble residue (1-20% of the rock) of selected phosphatic samples from the Hor Hahar field, Negev, southern Israel. Clinoptilohte occurred mainly in the ‘sterile intercalations’. Inasmuch as clinoptilohte has not been identified in older formations in the Negev, it was presumed to be authigenic in the Mishash Formation.
Estudio del orden-desordern en una nontronita potasica anhidra por difraccion de rayos x
Authors: de la Calle C. 
Published: December 2006

ResumenLa determinación del orden o desorden en la dirección perpendicular a las láminas en una nontronita anhidra ha sido efectuada a partir de las reflexiones 001 y 003 y de una parte de la difusión a pequeños ángulos. Mediante la comparación de diagramas experimentales y curvas calculadas a partir de modelos, se pretende poner en evidencia si el sistema es ordenado o desordenado y en el segundo caso la manera de establecer un modelo que traduzca el desorden del sistema. Se llega a la conclusión de que la nontronita potásica anhidra es un sistema desordenado en la dirección perpendicular a las láminas en el que aparecen espaciados correspondientes a varias distancias discretas afectadas por proporciones determinadas.
Clay particle sizing by electrically-induced birefringence
Authors: Oakley D. M. , Jennings B. R. 
Published: December 2006

AbstractUnder the influence of a pulsed field, dilute clay sols become birefringent as the particles undergo orientational order. The rate of decay of the birefringence on removal of the field is characteristic of the particle geometry. Measurement of the decay rates under two specific experimental conditions provides sufficient information from which the particle-size distribution can be evaluated in terms of a two-parameter function. Experimental data are reported and analysed in terms of a log-normal distribution of particle sizes for attapulgite (rods), kaolinite (discs) and halloysite (ellipsoids) sols and compared with success to electron microscopic data. The ability of the method to determine size distributions in terms of the major dimensions of the clay particles, rather than those of the often used equivalent sphere, is highlighted.
Formation and distribution of Mg, Fe, Mn-smectites in the first stages of the lateritic weathering of forsterite and tephroite
Authors: Nahon D. , Colin F. , Tardy Y. 
Published: December 2006

AbstractDuring weathering of forsterite and tephroite under the humid, tropical conditions of the Ivory Coast, intermediate Mg,Fe3+− or Mn2+-smectites appear prior to widespread development of iron or manganese oxyhydroxides. In forsterite, the smectite varies from an Mg-trioctahedral variety near the centres of altered crystals to an Mg,Fe3+,Al-di/trioctahedral variety near the edges. The Al-content of this latter smectite is supplied by dissolution of adjacent minerals, notably enstatite. An Mn2+-trioctahedral smectite forms in cracks in tephroite crystals.
Selective extraction of amorphous iron oxides by EDTA from selected silicates and mixtures of amorphous and crystallline iron oxides
Authors: Borggaard O.K. 
Published: December 2006

Amorphous iron oxides in soil are often extracted by an ammonium oxalate solution (Schwertmann, 1964). This treatment may, however, also dissolve crystalline iron oxides and iron silicates (McKeague & Day, 1966; Baril & Bitton, 1969; McKeague et al., 1971; Arshad et al., 1972; Pawluk, 1972; Schwertmann, 1973; Taylor & Schwertmann, 1974; Borggaard, 1976).It has been shown that EDTA can selectively extract amorphous iron oxides from soils (Borggaard, 1979, 1981) and a synthetic mixture of amorphous iron oxide, goethite, and hematite (Borggaard, 1976). As pointed out previously (Borggaard, 1979), the EDTA method should also be tested on selected minerals to decide if it can serve as a reference method against which other less time-consuming methods may be tested.
Stabilization of colour and structure in the pyroaurite-type compounds Fe(II)Fe(III)Al(III)-hydroxycarbonates
Authors: Taylor R. M. 
Published: December 2006

Green-blue Fe(II)Fe(III)-and Fe(II)Al(III)-hydroxycarbonates with a pyroaurite structure were prepared by Taylor & McKenzie (1980) and Taylor (1980). They were thought to be related to the unstable mineral phases which occur naturally in the dark green-blue mottles of wet, anaerobic horizons of gleyed soils. These synthetic compounds are unstable to oxidation, suffering structural and colour changes, with the ultimate products depending on the environmental conditions. This instability makes it difficult to identify them and study their characteristics by X-ray diffraction and other methods.The technique described in this note has been found to stabilize the synthetic green-blue compounds satisfactorily. It involves handling and storage of the compounds in a CO2 atmosphere, such as might occur under natural anaerobic conditions in a soil below the ground-water level. The same principles can be applied to collect field samples and maintain them in a stable state.
The quantitative phase analysis of clay minerals by X-ray diffraction: modern aspects of industrial routine control
Authors: Minichelli D. 
Published: December 2006

AbstractThe method described uses external standard mixtures, both natural and artificial. Variations in degree of structural order between standard and analyte mineral are taken into account. ‘Amorphous’ materials in standard mixtures are simulated by alkali-boron-silicon glasses. Variations in response of the X-ray equipment with time are assessed by running a standard multiphase mixture. Strict control is exercised on particle orientation, and thermal treatments are used to separate overlapping reflections in the low-2θ region.
On the nature of fibrous illite as observed by electron microscopy
Authors: Huggett J. M. 
Published: December 2006

AbstractIn a study of sandstones from the Coal Measures (Westphalian A and B) of the East Midlands, UK, fibrous illites exhibiting random core and lath structures were observed during SEM examination of material dried in air, but not during TEM examination of ultrathin sections made from the same material. Previous studies have reported random core and lath structures during TEM examination of extracted clay material and it is suggested that they are an artefact of the specimen preparation technique.
The point of zero charge of natural and synthetic ferrihydrites and its relation to adsorbed silicate
Authors: Schwertmann U. , Fechter H. 
Published: December 2006

The point of zero charge (pzc) of synthetic Fe-oxides is well documented and usually ranges between pH 7 and 9 (Parks, 1965; Schwertmann & Taylor, 1977). In contrast, the pzc of natural Fe-oxides has only rarely been determined. Using electrophoretic mobility, Van Schuylenborgh & Arens (1950) found that a natural goethite had a much lower pzc (∼3) than synthetic goethites. They attributed this to better crystallinity of the natural goethite caused by slower crystallization. Soils dominated by Fe- (or Al-) oxides rarely have pzc values as high as those of pure oxides. This is usually attributed to the presence of negatively charged impurities such as clay silicates and organic matter (Parfitt, 1981).Ferrihydrite, a natural, poorly-crystalline Fe-oxide mineral of bulk composition 5Fe2O3.9H2O, occurs in hydromorphic soils (Schwertmann et al., 1982) and is the main component in ochrous precipitates formed when Fe-bearing fresh waters come in contact with air (Schwertmann & Fischer, 1973; Carlson & Schwertmann, 1981). Under these conditions the ferrihydrite is reasonably free of other charge-active minerals. The aim of this study was to find out if the pzc of these natural ferrihydrites differed from those of synthetic samples.
Structural aspects of the hisingerite-neotocite series
Authors: Eggleton R. A. , Pennington J. H. , Freeman R. S. , Threadgold I. M. 
Published: December 2006

AbstractTransmission electron microscopy, X-ray radial distribution function analysis, chemical analysis, X-ray absorption edge spectroscopy, and Mössbauer spectroscopy combine to confirm an amorphous or gel structure for minerals of the hisingerite-neotocite series: (Fe,Mn)0.8SiO3.1.2H2O. A framework of (Fe,Mn)O6 octahedra and [SiO4] tetrahedra form hollow spheres, 50–100 Å in diameter, cross-bonded into a physically isotropic solid with as much as 10% interconnected pore space. The outer 10–20 Å of the spheres has a rudimentary structure, possibly marking the onset of segregation into Si-rich and (Fe,Mn)-rich layers. The Broken Hill mineral ‘sturtite’ is an intermediate member of the hisingerite-neotocite series.
Laboratory separation of clays by hydrocycloning
Authors: Bain J. A. , Morgan D. J. 
Published: December 2006

AbstractAlthough seldom appreciated, the hydrocyclone offers several advantages over the more commonly used sedimentation/decantation method for clay separation. Large amounts of relatively concentrated clay suspensions may be separated in a matter of minutes. In addition, no dispersing agents are required and the shear conditions encountered by the suspension during passage through the hydrocyclone lead to particle disaggregation both in the silt and sub-micron size range. Formulae relating design factors of the hydrocyclone to separation performance exist but are of limited value as they are unable to predict the maximum particle size of the clay product or percentage recovery of any particular size of particle. Such data, determined from practical trials, are given for kaolinite, smectite and mixed-assemblage clay suspensions. Design limitations prevent the effective separation of clay products with ‘cut-off’ sizes finer than 5 µm.