bluuebunny/crossref_metadata_2025 huggingface dataset:
The application of electron spin resonance spectroscopy to studies of clay minerals: II. Interlamellar complexes—structure, dynamics and reactions
Authors: Hall Peter L.
Published: December 2006

A review is given of the application of ESR spectroscopy to the study of hydrated transition metal ions and nitroxide spin probes in the interlamellar region of smectites and vermiculites. These investigations have not only provided information regarding the structure and mobility of the intracrystalline water-cation layers but have also demonstrated the reactivity and catalytic properties of certain transition metal exchange forms of smectites. Several novel coordination complexes and redox reactions between the exchange ions and a variety of simple organic molecules have been characterized.
Influence des proprietes des charges kaoliniques sur les performances des caoutchoucs naturels charges
Authors: Yvon J. , Cases J. M. , Lietard O. , Garin P. , Lhote F.
Published: December 2006

Après avoir défini la notion de charge minérale, on étudie la nature et le nombre des défauts cristallins d'argiles kaoliniques. On montre l'influence des défauts d'empilement (interstratification de feuillets potassiques) et des défauts dans le plan (conséquence des substitutions de l'aluminium) sur les propriétés mécaniques des caoutchoucs chargés. Puis on étudie l'influence de la pureté minéralogique et de certains paramètres superficiels sur les performances des produits chargés. Enfin, on propose des méthodes de traitement qui permettent d'accroître les propriétés renforçatrices de la charge. On présente l'évolution comparée de 64 paramètres descriptifs de la charge et du produit fini en définissant des guides de prospection et de traitement qui permettent l'utilisation optimale des réserves charentaises dans le domaine des caoutchoucs naturels.
Formation and properties of Fe(II)Fe(III) hydroxy-carbonate and its possible significance in soil formation
Authors: Taylor R. M.
Published: December 2006

Small amounts of Fe(III) induce precipitation of Fe(II) from carbonate solutions around neutral pH values. The reaction involves the formation of Fe(II)Fe(III) hydroxycarbonate, a green, layer-structured compound of the pyroaurite group of minerals. Variations in the concentration of Fe(II) in the solution phase, and in the form and amounts of the total Fe(III) in the system, may cause other phases such as magnetite and siderite to form also. Freeze-dried Fe(II)Fe(III) hydroxy-carbonate undergoes topotactic alteration to a magnetic phase, presumably maghemite, when stored under vacuum. The compound is readily oxidized in air in either the moist or dry state, rapidly becoming yellow or yellow-brown in colour. Oxidation leads to the formation of either goethite, lepidocrocite, ferrihydrite or mixtures of these phases, depending on the mode of oxidation and the impurities present. The similarity between the rapid colour changes and the oxidation products of the blue-green precipitates in gleyed soil horizons and this Fe(II)Fe(III) hydroxy-carbonate leads to the speculation that this and related compounds may be the meta-stable precipitates in such soils, rather than a previously postulated hydro-magnetite phase. Eh and pH conditions for the formation of Fe(II)Fe(III) hydroxy-carbonate are given, and are in the range encountered in the soil environment.
Characterization of clays by organic compounds
Authors: Lagaly G.
Published: December 2006

Many problems—from soil research to ceramics—require a reliable characterization of the clay minerals involved. This can be done using four clay-organic reactions: (i) staining tests and dye adsorption; (ii) glycerol and glycol adsorption; (iii) intercalation; (iv) alkylammonium ion exchange. Dye adsorption (staining tests) and glycerol adsorption allow a preliminary identification of the clay mineral groups. Intercalation reactions indicate minute differences between kaolins which cannot be detected by XRD and DTA. Alkylammonium ion exchange provides the best method for characterizing smectites and is sensitive to changes in the layer charge.
Utilisation du rayonnement synchrotron en diffusion aux petits angles pour l'étude du gonflement des smectites: I. Etude du systeme eau-montmorillonite-Na en fonction de la temperature
Authors: Pons C. H. , Rousseaux F. , Tchoubar D.
Published: December 2006

Resume

Nous proposons l'étude du mècanisme de gonflement d'une smectite, basée sur l'exploitation des diagrammes de diffusion aux petits angles obtenus avec la source de rayons X synchrotron de Lure (Orsay). Cette technique a permis d'étudier le gonflement, en fonction de la température, d'une montmorillonite Na, en suspension dans l'eau et concentrée à 20%.

L'analyse des diagrammes est éffectuée par une méhode basée sur la comparaison des courbes expérimentales à des courbes théoriques. Les modèles de structure permettant le calcul des diagrammes théoriques fait appel à la notion de particule (définie comme un empilement de feuillets parallèles) et de structure interne de la particule (définie par un ensemble de translationsdiaffectées des probabilitéspiqui déterminent la position mutuelle des feuillets).

Les résultats montrent qu'à basse température, les particules de très grande taille sont constituées par la superposition de sous empilements, comportant 4 à 5 feuillets, hydratés d'une manière homogène et se désorientant mutuellement pour former la structure du gel. On explique ainsi que la structure du gel formé est correlée avec celle du solide initial et que le phénomène de gonflement est quasi réversible.
Formation of gibbsite in soils and saprolites of temperate-humid zones
Authors: Macías Vazquez F.
Published: December 2006

Analysis of the distribution of gibbsite in soils and saprolites of Galicia, NW Spain, leads to the conclusion that this mineral is mostly formed by inorganic mechanisms in open, well-drained and desaturated systems in the initial stages of weathering of various aluminosilicates, especially plagioclases. No evidence has been found to support the hypothesis that it is a feature inherited from hotter climates, as it has not been identified to date either in ancient sediments or in the most evolved and weathered soils. The role of organic matter and the possibility ofa biogeochemical origin is also discussed: it is considered that this mechanism is only important during podsolic soil development.
Variation du parametrebet de la distance basale d001dans une serie de saponites a charge croissante: I. Etats hydrates
Authors: Suquet H. , Malard C. , Copin E. , Pezerat H.
Published: December 2006

Neuf saponites synthétiques ont été utilisées pour étudier l'influence des substitutions Si-Al sur le paramètrebet la distance basale d001des phyllosilicates 2/1 trioctaèdriques. Dans les saponites hydratées à deux couches, le paramètre best le résultat des interactions entre couches octaèdrique et tétraèdriques. Dans les saponites hydratées à une couche, il dépend non seulement des paramètres des couches octaèdrique et tétraèdriques mais encore de la nature de la couche interfoliaire. L'effet du cation interfoliaire varie avec sa taille et sa localisation dans l'espace interfoliaire.
Origen de niveles continentales silicificados con alunita en el Preluteciense de Salamanca España
Authors: Saavedra J. , Sanchez Camazano M.
Published: December 2006

Los 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

A 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

Resume

Huit 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

Four 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

Porewater 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

Scanning 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

The 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

The 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

The 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

Different 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

A 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.
The texture of an english fuller's earth
Authors: Robertson R. H. S. , Tessier D. , White J. L.
Published: December 2006

It is generally agreed that the English mid-Jurassic and Lower Cretaceous fuller's earths were derived from volcanic ash. In the Lower Cretaceous fuller's earth of Woburn, Kerr (1932) recognized partially decomposed relics of shards in a matrix of montmorillonite, and Grim (1933, 1935) described montmorillonite pseudomorphs after glass fragments in the Bath fuller's earth of Bathonian age. Jeans et al. (1977) published twenty-two SEM pictures of pyroclasts, including sanidine, sphene, trachytic pumice, and a basaltic glass fragment. Photomicrographs of the Lower Cretaceous fuller's earth show shard relicts ranging in length from 0·8-1·26 mm (median ∼1·12 mm) and in thickness from 5-15µm (Jeans et al., 1977, fig. 14a). However, much remains obscure about the shape, size and mode of packing of the argillized vitric particles which make up the bulk of fuller's earths. This note describes the texture of an English fuller's earth which was freeze-fractured (Tessier, 1978), prior to examination with a scanning electron microscope.
Estudio del orden-desordern en una nontronita potasica anhidra por difraccion de rayos x
Authors: de la Calle C.
Published: December 2006

La 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

Under 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

During 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 recognition of volcanic clays and the significance of heavy minerals
Authors: Spears D. A.
Published: December 2006

The explosive ejection of material from a volcanic vent produces pyroclastics. These are stratigraphically important because of their isochronous nature, lateral extent and potential for absolute age determinations. The pyroclastics also provide information on the nature of the volcanic activity, which is possibly the only record because of non-preservation in other areas. The recognition of pyroclastics is therefore important, but often difficult,because the high-temperature igneous material is susceptible to alteration in the diagenetic environment. In Quaternary sediments the composition of glass shards is an important aspect of tephrochronology (Westgate & Briggs, 1980) but in older sediments glass shards are usually altered to clay minerals. Exceptionally, shards are preserved unaltered, as in the case of early carbonate and silica cementation (Francis et al., 1968; Jeans et al., 1977). According to Ross (1928), features that are diagnostic for the recognition of a volcanic clay (bentonite is the term used by Ross) are, in order of apparent reliability: (i) presence of glass relict structure; (ii) presence of minerals and crystal forms characteristic of volcanic rocks, including biotite, feldspar, pyroxenes and hornblende; (iii) absence of minerals that do not have a volcanic origin, including microcline, garnet, muscovite, kyanite and andalusite; (iv) waxy lustre; (v) reaction to water; (vi) optical properties; (vii) chemical properties.
The quantitative phase analysis of clay minerals by X-ray diffraction: modern aspects of industrial routine control
Authors: Minichelli D.
Published: December 2006

The 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

In 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

Transmission 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

Although 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.
Structure and swelling of fibrous and granular saponitic clay from Orrock Quarry, Fife, Scotland
Authors: Cowking A. , Wilson M. J. , Tait J. M. , Robertson R. H. S.
Published: December 2006

Veins of intimately associated fibrous and granular saponitic clay occur in a basalt quarry at Orrock, Fife, Scotland. Preliminary X-ray diffraction studies suggested that both fibrous and granular forms consisted of pure saponite but chemical and thermal studies showed the presence of subsidiary amounts of interstratified chlorite. The fibrous clay, which is strongly oriented around the a axis but with a uniform distribution of the b and c poles, consists mainly of highly-crystalline laths with minor amounts of turbostratically-ordered particles. The granular clay consists of turbostratically-ordered particles only. The swelling behaviour of both types of clay in water and in ethylene glycol is similar to that of pure saponite. With glycerol, only the granular clay swells completely but the fibrous clay behaves similarly if first subjected to grinding or chemical pre-treatment. These observations are accounted for on the basis that the fibrous clay has better order than the granular form, thus enabling the interlamellar constituents to participate more fully in layer-to-layer bonding.
Relation entre le parametre b des smectites et leur contenu en fer et magnesium. Application a l'etude des sediments
Authors: Desprairies A.
Published: December 2006

Resume

Le paramètrebdes smectites, à charge faible et empilement désordonné, est déterminé dans les diagrammes de diffraction X à partir des maxima d'intensité de la bande (06,33); ce paramètre montre une très bonne corrélation avec la teneur en fer et magnésium des feuillets. Les équations de régression proposées sont applicables à tous les échantillons renfermantune ou plusieursvariétés minéralogiques du groupe. La méthode semble particulièrement bien adaptée aux études des transformations chimiques des sédiments, au cours, par exemple, de leur diagénèse.
Proprietes de reflexion diffuse de pates de kaolinite en fonction de leur teneur en eau
Authors: Prost R. , King C. , D'hellencourt T. Lefebvre
Published: December 2006

Resume

Le spectre de réflexion diffuse de pâtes de kaolinite obtenues pour des teneurs en eau croissantes a été étudié en séparant la part due au phénomène d'absorption de celle due à d'autres phénomènes comme la diffusion. On montre que l'intensité des bandes d'absorption varie linéairement avec la teneur en eau jusqu'à ce que le point d'entrée d'air dans le système soit atteint. Au-delà du point d'entrée d'air, quand le système est saturé en eau, l'intensité des bandes d'absorption semble tendre vers une limite. On montre de même que l'intensité réfléchie-diffusée en dehors des bandes d'absorption tend elle aussi vers une limite quand le système est saturé en eau. Il en résulte: (i) que la détermination des teneurs en eau à partir des données de réflexion diffuse est possible grâce à l'existence de courbes d'étalonnage linéaires dans le domaine d'hydratation pour lequel le système n'est pas saturé en eau, (ii) que l'analyse quantitative des données de réflexion diffuse est plus facile lorsque le milieu est saturé en eau. Les résultats obtenus montrent en outre que la relation générale proposée par P. F. Low: J = J0
eα/θ;
où où J est une propriété de l'eau associée avec l'argile, J
0 une même propriété pour l'eau liquide, θ; la teneur en eau et α un coefficient, ne s'applique que sur un domaine limité de teneurs en eau.
Genesis of bentonites from Cabo de Gata, Almeria, Spain: a stable isotope study
Authors: Leone G. , Reyes E. , Cortecci G. , Pochini A. , Linares J.
Published: December 2006

Oxygen (18O/16O) and hydrogen (2H/1H) isotopic ratios were measured on 22 smectite separates from bentonite deposits of the Sierra de Gata and Serrata de Nijar, Almeria, Spain. In addition, 18O/16O and 2H/1H ratios were determined on some waters from springs and wells, and 18O/16O ratios were measured on quartz, plagioclase and biotite samples separated from the bentonites. The smectites displayed two distinct isotopic compositional groups which excluded an origin either by submarine alteration or weathering under normal surface conditions of the associated volcanic rocks. Bentonization processes caused by low-temperature fluids of meteoric origin could account for the stable isotopic contents. Argillization temperatures are estimated at ∼40°C and ∼70°C for the Serrata de Nijar and the Sierra de Gata deposits, respectively.
The nature and origin of authigenic smectites in some recent marine sediments
Authors: Cole T. G. , Shaw H. F.
Published: December 2006

Three principal modes of formation are apparent for authigenic smectites in Recent marine sediments: alteration of volcanic rocks and glass, low-temperature combination of biogenic silica and Fe-oxyhydroxides, and direct precipitation from hydrothermal fluids. The latter two mechanisms are discussed with reference to new evidence from studies of sediments from the Bauer Deep of the equatorial eastern Pacific and the Atlantis II Deep in the Red Sea. In the Atlantis II Deep sediments, three sub-environments of smectite formation from hydrothermal fluids are recognized. In two of them nontronites are formed, whilst in the third an Fe-poor smectite, intermediate in composition between beidellite and montmorillonite, occurs.
Sorption and transformation of phenols on clay surfaces: effect of exchangeable cations
Authors: Isaacson P. J. , Sawhney B. L.
Published: December 2006

The sorption and transformation of phenol, 2-methylphenol, 3-methylphenol, 2,6-dimethylphenol, 3,5-dimethylphenol, and 2,4,6-trimethylphenol, by homoionic Na-, H-, Ca-, Cu-, Al-, and Fe(III)-montmorillonite from both vapour and aqueous phases were examined by IR spectroscopy. All the phenols were sorbed by the clays but were modified to different degrees depending on the exchangeable cations and on the amount and type of alkyl substitution of the phenols. Sorption of 2,6-dimethylphenol from aqueous solution was irreversible, and the extent of sorption followed the order Fe- > Al- > Cu- > Ca-clay. Both transition and non-transition metal cations were effective in transforming the phenol sorbates and heating the clay/phenol complexes further enhanced transformation. The results are discussed in terms of the nature of the transformation products and the likely role of radical reactions in their formation.
Evolution des biotites en fonction des conditions d'oxydo-reduction du milieu
Authors: Vicente-Hernandez J. , Vicente M. A. , Robert M. , Goodman B A.
Published: December 2006

Resume

Des études expérimentales sont réalisées afin de préciser les relations entre la vermiculitisation des biotites (ouverture par NaCl N) et les phénomènes d'oxydation (par l'eau ou par H2O2). Les évolutions sont suivies par diffraction des rayons X et en spectroscopie d'absorption infra-rouge; l'oxydation du fer est appréciée sur l'échantillon par spectroscopie Mössbauer. Les résultats montrent que si une certaine oxydation accompagne normalement la vermiculitisation, une oxydation intense provoque une expulsion de fer et la formation de vermiculite hydroxy ferrique.
The influence of aluminium substitution and crystallinity on the Mössbauer spectra of goethite
Authors: Murad E. , Schwertmann U.
Published: December 2006

Both aluminium substitution and poor crystallinity reduce the magnetic hyperfine field of goethite. Mössbauer spectra taken at 4·2 K show that the effect of poor crystallinity is similar to that of Al substitution, i.e. it reduces the saturation hyperfine field. A multiple correlation was found to exist between the magnetic hyperfine field at 4·2 K as a dependent variable vs Al substitution and crystallinity as independent variables. If a hyperfine field is to be interpreted with respect to either Al substitution or crystallinity, it is therefore necessary to have knowledge of the other variable.
The characterization of clay-organic systems
Authors: Tennakoon D. T. B. , Schlögl R. , Rayment T. , Klinowski J. , Jones W. , Thomas J. M.
Published: December 2006

The importance of a number of techniques (including1H and13C NMR, XRD and IR) in exploring the important catalytic properties of synthetic and natural clays is described. A clear distinction is observed between proven catalytically-active clays (e.g. Al-exchanged) and those which are generally less effective (e.g. Na-exchanged).13C NMR spectroscopy is used to identify directly products formed within the interlayer regions, and temperature-controlled powder XRD serves as a useful tool for identifying whether or not intercalation occurs under variously defined conditions. High-pressure XRD is used to verify the formation of different products during reaction.
Smectite-polymer interactions in aqueous systems
Authors: Burchill S. , Hall P. L. , Harrison R. , Hayes M. H. B. , Langford J. I. , Livingston W. R. , Smedley R. J. , Ross D. K. , Tuck J. J.
Published: December 2006

Neutron scattering studies have indicated that the non-coordinated water at smectite surfaces has a similar mobility to that of bulk water, but that the water coordinated to the cations is immobile on the time scale of the neutron measurements. Thus hydrophylic polymers can readily displace the non-coordinated water and bind to the silicate surface, and to the exchangeable cations through a water-bridge mechanism. Poly(ethylene oxide) molecules with molecular weights up to 4000 appear to be bound to Na-montmorillonite in flattened conformations at the clay surface. Poly(vinyl alcohol) is extensively bound by Na-montmorillonite and by Na-Laponite (a synthetic hectorite-like clay); as binding progresses fewer molecule segments can contact the surface and so at the higher levels of adsorption extensive loops of polymer extend away from the silicate surface. Some polyanions provide good protection for smectites against flocculation with salt. The abilities of such polymers to protect the clays is dependent both on the extents of the charges and on the solution conformations which these polymers can assume.
Synthetic imogolite: properties, synthesis and possible applications
Authors: Farmer V. C. , Adams M. J. , Fraser A. R. , Palmieri F.
Published: December 2006

The unique properties of imogolite are closely related to its structure, which is a tube of 23–27 Å outer diameter and ∼10 Å inner diameter, with an AIOH outer surface and SiOH inner surface. Acid dispersions contain the long, positively-charged tubes as isolated units or small bundles, which form bulky gels in alkali, and flocculate with negatively-charged colloids, polyvalent anions, and long-chain anionic detergents. Sorption properties are associated with the 10 Å intra-tube pores and with inter-tube channels of variable dimensions. Surface acidity is less than that of layer-silicate clays. The chemical and mechanical stability, biological activity, film- and fibre-forming characteristics, and conditions of synthesis are reviewed, on the basis of both new and published findings. Areas of potential application are indicated.
Kaolinites ferriferes et oxy-hydroxydes de fer et d'alumine dans les bauxites des Canonnettes (S.E. de la France)
Authors: Cantinolle P. , Didier P. , Meunier J. D. , Parron C. , Guendon J. L. , Bocquier G. , Nahon D.
Published: December 2006

Resume

L'analyse par diffraction des rayons X, résonance paramagnétique électronique et par spectrométrie infra-rouge des constituants minéraux du profil des Canonnettes (Sud-Est de la France) permet de montrer que les kaolinites sont ferrifères. De plus, au fur et à mesure du développement et de l'accumulation des oxy-hydroxydes de fer et d'alumine dans le profil, on note l'enrichissement progressif des kaolinites en fer en même temps qu'augmente leur désordre et que les taux de substitution en moles % d'AlOOH des goethites alumineuses devient plus important. Finalement, les kaolinites disparaissent remplacées par les oxy-hydroxydes de fer et d'aluminium, là ou leur accumulation est maximum.
Ferrous-iron-bearing vermiculite-smectite series formed during alteration of chlorite to kaolinite, Otago Schist, New Zealand
Authors: Craw D.
Published: December 2006

Interlayered (<20 µm scale) vermiculite-smectite minerals were found in drill-cores from altered Otago schist basement up to 2 m from the contact with the overlying sediment. Mineral compositions defined a series from Fe2+-rich trioctahedral vermiculite to Fe2+-bearing dioctahedral smectite; in these, tetrahedral substitution of Al for Si was unusually high (up to 3·3/8 in the formula unit). The minerals formed as intermediates during the alteration of chlorite to kaolinite under non-oxidizing, possibly acid conditions. The source of the altering solutions may have been overlying lignite seams.
Comportement des ions aluminiques et de la silice en solution: Etude de la formation de la kaolinite
Authors: Espiau P. , Pedro G.
Published: December 2006

Resume

L'intérêt porté à la synthèse de la kaolinite a été suscité par des préoccupations d'ordre pédologique, qui nous ont amenés à comparer les expériences réalisées en laboratoire aux situations naturelles considérées comme propices à la formation de la phyllite 1/1. Il apparaît essentiel, pour le succès des synthèses, de privilégier la formation d'ions hydroxylés monomères de Al, pouvant réagir avec l'acide orthosilicique. La neutralisation lente et partielle de solutions très diluées semble garantir ces conditions. Deux séries d'essais ont été entrepris. Les résultats expérimentaux tendent à démontrer la possibilité d'obtenir une précipitation de kaolinite à partir des ions en solution et par simple neutralisation. Le mécanisme proposé par Siffert (1962), mettant en jeu la formation d'éléments T-O, semble le plus probable. Ces éléments prendraient naissance par réaction de l'acide orthosilicique et de l'ion Al(OH)2+. Le rapprochement entre l'importance du rôle joué ici par ce monomère hydroxylé et la place qu'il occupe dans le schéma de dissolution établi par Sarazin (1979) peut permettre de comprendre que les néoformations de kaolinite correspondent à des sols relativement bien drainés.