bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cadre géologique et minéralogie des argiles des Charentes, France
Authors: Dubreuilh J. , Marchadour P. , Thiry M. 
Published: December 2006

ResumeDes kaolinites sont exploitées dans les sédiments du Tertiaire inférieur des Charentes, constitués d'argiles, de lignites, de sables noirs à gros bois et pyrite et de sables roux. Deux niveaux de kaolinite sont exploités: (i) des kaolinites ordonnées accompagnées de muscovite, (ii) des kaolinites désordonnées toujours accompagnées d'anatase. Ces deux niveaux correspondent à deux épisodes sédimentaires successifs, datés du Sparnacien et du Cuisien par la palynologie. Le premier épisode est vraisemblablement issu de la reprise d'altérations éablies sur le socle cristallin du Massif Central, alors que le second reprendrait des matériaux issus de l'altération des roches sédimentaires des bordures du bassin. Des kaolinites très bien ordonnées et de la gibbsite résultent de transformations géochimiques au sein des dépôts. Elles sont liées aux milieux acides des dépôts ligniteux et à l'oxydation des pyrites qui amènent la mobilisation de l'aluminium.
An iron-free volkonskoite
Authors: Khoury H. N. , Mackenzie R. C. , Russell J. D. , Tait J. M. 
Published: December 2006

AbstractA green smectitic mineral from Jordan with 16% Cr2O3 (almost 22% on an ignited basis) has been shown by chemical, X-ray, electronoptical, electron microprobe, infrared and thermoanalytical evidence to be an iron-free volkonskoite of composition:1·06 M+(Si7·39Al0·61)(Cr2·20Mg2·52)O20(OH)4.The octahedral occupancy of 4·7, with only Mg2+ and Cr3+ in octahedral positions (in a ratio of 1·14), suggests that the mineral is intermediate between di- and trioctahedral—an inference supported by the uniformity of composition of individual particles (as revealed by the microprobe) and IR evidence, which indicates that it is predominantly dioctahedral but with certain trioctahedral characteristics. A volkonskoite sample from the type area in the USSR, examined for comparison, contained 23·5% Cr2O3 (about 29% on an ignited basis), but proved on electron microprobe examination to be a mixture of at least three species, one of which was aluminium-rich. IR and thermoanalytical characteristics are discussed in relation to the existence of tri-dioctahedral species.
Interpretation of the optical absorption spectrum of
Ni-substituted lizardites
Authors: Julg A. , Julg O. 
Published: December 2006

The spectrum of Ni-substituted lizardite, (Mg,Ni)3Si2O5(OH)4, has been discussed by many authors, who have successively given contradictory interpretations concerning the symmetry of the Ni-sites. Lakshman & Reddy (1973) affirmed that in garnierites Ni is in a tetrahedral site. Faye (1974) rejected this conclusion and showed that Ni2+ occupies an octahedral site. However, the Ni … O distance of 2·01 Å which he deduced from the intensity of the crystal field is unacceptable. Recently, using a completely different approach to the interpretation of the spectrum, Cervelle & Maquet (1982) claimed that Ni2+ occupies a six-coordinated site of C3v symmetry, and concluded that the mean Ni … O distance is 2·06 Å.The aim of this note is to show that it is possible to interpret the spectrum of Ni-lizardite as arising from a predominantly octahedral field with a weak C2v component which provokes a small increase in width of the absorption bands.
Distinction of tetrahedrally and octahedrally coordinated Al in phyllosilicates by NMR spectroscopy
Authors: Sanz J. , Serratosa J. M. 
Published: December 2006

In recent years, the availability of high-field superconducting magnets complemented with mechanical spinning of the samples (magic-angle spinning technique) has resulted in a considerable improvement in resolution of NMR spectra and has widened the use of this technique in the structural analysis of solid samples. In particular, NMR spectroscopy can distinguish the different chemical environments of tetrahedrally coordinated silicon and also determine short-range order in the distribution of Si and Al in micas (Sanz et al., 1983) and zeolites (Fyfe et al., 1983; Klinowski et al., 1982).For aluminium (I = 5/2), the existence of strong quadrupolar interactions means that, in general, only the m½↔m−½ transition is observed. However, the signal is broadened by second-order quadrupolar effects, dipolar interactions and chemical shift anisotropies.
Interactions of halloysites with amides: mineralogical factors affecting complex formation
Authors: Churchman G. J. , Theng B. K. G. 
Published: December 2006

AbstractComplex formation between halloysites, from soil and geological sources, and a series of amides has been investigated. All the amides used can be intercalated to give single-layer complexes with basal spacings between 10·4 Å (for formamide) and 12·4 Å (for N,N-dimethylacetamide). When the interlayer space of halloysite has already been expanded by water, as is the case with fully hydrated samples, the rate and extent of intercalation depend more on the properties of the organic species than on the mineralogy of the clay. With partially and completely dehydrated halloysite, however, complex formation is influenced by the particle size, crystallinity, and iron content of the mineral. A large particle size, a high degree of crystallinity, and a low iron content are all conducive to complex formation. The iron content of halloysite also appears to affect particle shape. Low structural iron contents are associated with long tubular particles, intermediate contents with short and/or wide tubes, and high contents with spheroidal and other non-tubular forms. Halloysites containing high amounts of extractable (non-structural) iron generally show a low intercalating ability.
Mixed-layer illite-smectite in low-temperature diagenesis: data from the Miocene of the Carpathian Foredeep
Authors: Środoń J. 
Published: December 2006

AbstractBulk mineralogy, clay fraction mineralogy and layer ratio in interstratified illite-smectite were studied in three Upper Miocene profiles, up to 200 m deep and representing very low sedimentation rates (∼80 mm/103 yr) with environments of sedimentation ranging from hypersaline (gypsum deposits) to brackish. No correlation was found between mineralogy and depth, or between mineralogy and chemical environment of deposition, despite the use of precise identification techniques. It is concluded that smectites and interstratified illite-smectites are stable in marine sediments until the elevated temperatures of deep diagenesis are reached.
Etude du biopyribole formé par chauffage des vermiculites magnésiennes
Authors: Suquet H. , Mallard C. , Quarton M. , Dubernat J. , Pezerat H. 
Published: December 2006

RésuméLes vermiculites magnésiennes chauffées durant plus de 24 h à une température de 700°C dans l'air, donnent une phase non gonflante qui est un biopyribole. Les diagrammes de diffraction X obtenus avec un monocristal montrent que ce matériau est constitué de deux phases: une enstatite en épitaxie sur le plan (010) d'un phyllosilicate. Le phyllosilicate a un empilement des feuillets semi-ordonné. Les rangées du plan (h0l) éant entièrement discrètes, la projection x0z a été étudiée par une analyse de Fourier classique à deux dimensions. Les autres rangéés du réseau réciproque sont plus ou moins diffuses dans la direction c*. Le désordre est creéé par une distribution aléatoire de trois translations entre les feuillets adjacents. Les relations structurales existant entre le phyllosilicate et l'enstatite expliquent l'absence de propriétés de gonflement de la phase phyllosilicate du biopyribole.
An IR cell for vacuum and high temperature
Authors: Lugli W. 
Published: December 2006

Much interest has been shown in IR cells capable of maintaining one or more samples at constant temperature, constant water vapour or gas pressure, or under vacuum conditions (Farmer, 1974). This note describes a cell capable of maintaining a vacuum between 10-3 torr and 10-4 tort from room temperature to 1000°C whilst the spectrum is being recorded; such cells have been constructed previously but for less severe conditions.The cell and associated vacuum system are shown schematically in Fig. 1. The vacuum in the cell body is produced by an Edwards rotary pump and a normal mercury diffusion pump. To obtain a vacuum of 10-3 to 10-4 torr, a liquid nitrogen trap and foreline trap are used. The trap is filled with activated alumina. The O-ring seals in the cell are made of Viton. The constant vacuum control is obtained with Pirani and Penning gauges.
Obtention de la fonction de modulation experimentale pour les gels de smectites contenant du fer
Authors: Rhaiem H. Ben , Pons C.H. 
Published: December 2006

Lors de l'étude du gonflement des smectites par analyse de la diffusion des rayons X aux petits angles, Ponset al.(1981) et Ben Rhaiem (1983) ont obtenu des diagrammes de diffusion caractérisés dans le domaine étudié par des modulations plus ou moins prononcées de la courbe d'intensité.L'analyse quantitative des courbes de diffusion, et en particulier de ces modulations, permet alors de remonter à une description de la structure du gel ou de la pâte et aux relations existant entre texture et structure (Ponset al., 1981; Ponset al., 1982). La méthode générale d'interprétation proposée par Ponset al.(1981) repose sur une comparaison entre intensité expérimentale et intensité théorique calculée à partir de modèles.
Controls on mineral authigenesis in Coal Measures sandstones of the East Midlands, UK
Authors: Hugget J. M. 
Published: December 2006

AbstractAuthigenic clay mineral formation in fluvial sandstones and one brackish sandstone from the lower and middle Coal Measures of the East Midlands has been studied using XRD, optical microscopy and a variety of electron optical techniques. The sandstones are quartz-rich with minor feldspar and mica. The clay minerals present are kaolinite, chlorite and illite; they form 10–15% by volume of most of the sandstones. Both detrital and authigenic illite and chlorite are present but the kaolinite is entirely authigenic. Kaolinite and illite authi-genesis has been important in all the sandstones but authigenic chlorite is only abundant in the phyllosilicate-rich Silkstone sandstone. The controlling factors in the diagenesis of the sandstones were primary composition, environment of deposition, bed thickness, pore-fluid migration and composition, pressure and temperature. These interacting factors have been of varying importance in time and space in the diagenesis of the sandstones. Authigenic clay morphology appears to have been controlled by time and environment of formation, pore-fluid chemistry and, possibly, parent minerals.
The nature, origin and distribution of authigenic clay minerals from Middle Jurassic Ravenscar and Brent Group sandstones
Authors: Kantorowicz J. 
Published: December 2006

AbstractMiddle Jurassic sandstones contain a variety of authigenic clay materials. The origin and distribution of these are related to the influence of several factors, principally depositional pore-fluid chemistry, sandbody geometry and the migration of aggressive fluids. Pore-lining illite, pore-lining chlorite and pore-filling vermiform kaolinite in the Ravenscar Group mutually exclude each other because of depositional pore-water chemistry; seawater in the case of the illite, anoxic freshwater in the case of chlorite and oxygenated freshwater in the case of the kaolinite. Blocky pore-filling dickite occurs ubiquitously within the large connected sandbodies. Its origin may be related to the migration of aggressive fluids and its distribution to depositional sandbody geometry. Mixed-layer chlorite-vermiculite also occurs, and is believed to have formed from chlorite during Recent weathering. Similar patterns occur in Ninian Field Brent Group sandstones, although the situation is more complicated (in these sandstones the kandite subgroup minerals are undifferentiated in this paper). Here too, pore-lining illite occurs in marine sandstones and pore-filling vermiform kandites in non-marine sandstones. However, vermiform kandites also occur in the marine sandstones, perhaps due to freshwater-table development following progradation. The more blocky kandites occur in large connected sandbodies. Finally, a second phase of illitization occurs, postdating blocky kandites, perhaps caused by alkaline formation waters. The occurrence of chlorite in the Broom Formation is anomalous and its possible origin is discussed.
Diagnetic history and reservoir quality of a Brent Sand sequence
Authors: Blackbourn G. A. 
Published: December 2006

AbstractThe Etive Formation of the Middle Jurassic Brent Group in part of the Northern North Sea comprises dominantly clean, fine- to medium-grained sands, deposited as part of a barrier-bar complex. The overlying Ness Formation was deposited on supra- or intertidal fiats, and comprises silty channel sands with silts, muds and thin coals. The sands of both Formations are mainly quartz-rich, with up to 12% by volume of feldspar, and variable proportions of clayey matrix. Early carbonate cementation preceded a phase of quartz overgrowth, which continued during burial. Later dissolution of unstable grains, dominantly feldspars, was followed by precipitation of pore-filling kaolinite and minor late-stage mineral phases. Better permeability of the Ness sands (up to 500 mD) relative to the Etive (mostly <10 mD) is mainly due to the effects of diagenesis on different lithofacies. Silty sands escaped intense quartz cementation and were thus more affected by acid groundwaters which improved permeability.
Patterns of diagenesis in the Sherwood Sandstone Group (Triassic), United Kingdom
Authors: Burley S. D. 
Published: December 2006

AbstractThe Triassic Sherwood Sandstone Group comprises a complex of continental red beds deposited by a major fluvial system flowing dominantly down a northerly inclined palaeoslope. Sedimentation took place in several distinct, tectonically active basins with varying maximum burial depths, ranging from shallow (<1 km) to deep (>3 km). Despite proximal to distal variations in stream type, a distinct suite of early diagenetic events can be recognized throughout all the depositional basins, which is related to the depositional environment. These events are best preserved in those basins with shallow burial histories, and show many similarities to the processes recorded from modern red beds of the Sonoran Desert, Baja California, although a more advanced grade of diagenesis has been reached in the Sherwood Sandstone. On the margins of the Irish Sea Basin in Cumbria, where burial was shallow, these early diagenetic textures are well preserved. The detrital grains underwent changes aimed at reaching equilibrium with the near-surface chemical environment. Unstable silicates were dissolved or replaced and the released ions were capable of precipitating authigenic phases, typically mixed-layer illite-smectite, K-feldspar, non-ferroan carbonates and hematite. Lateral variations in the early diagnetic assemblages reflect chemical and spatiotemporal changes ofinterbasin depositional and diagenetic environments. Deeply buried equivalents in the Irish Sea reached a maximum burial depth in excess of 3 km towards the end of the Mesozoic. Superimposed on the early diagenetic fabric are a series of depth-related changes. In the absence of early cements, compaction reduced porosity to low levels. Mixed-layer illite-smectites were converted to highly crystalline illites with low Fe and Mg contents. Early framework-preserving non-ferroan carbonates were extensively dissolved, generating widespread secondary porosity. Late pore-filling carbonate cements comprise ferroan dolomites and ankerites with compositions up to Ca(Ca0·02Mg0·43Fe0·53Mn0·02). Following late Mesozoic burial, inversion of the Triassic basins resulted in the re-exposure of basin margin sequences and shallow burial basins. Modern groundwaters are typically very dilute, with essentially neutral pH, and are capable of dissolving carbonate, sulphate and halite cements. In the Wessex Basin, however, the Triassic sandstones of the South Devon aquifer have been extensively modified by the percolation of post-inversion acidic groundwaters. These low-pH waters have resulted in thein situbreakdown of feldspar to produce abundant authigenic kandite, widespread dissolution of carbonate cements and removal of early-formed iron oxide cements. In contrast, the concealed, deeply buried eastern margin of the Wessex Basin exhibits a diagenetic evolution resultant of deep burial and has no development of authigenic kandite.
Interpretation of wireline log and core data from a mid-Jurassic sand/shale sequence
Authors: Peveraro R. C. A. , Russell K. J. 
Published: December 2006

AbstractInterpretation of downhole wireline logs is generally a major source of information used to build up a picture of the quality and distribution of reservoir rocks. Logging tools respond to a number of variables and comparison of a suite of different logs is usually required to isolate and identify the response due to a single factor, e.g. porosity or clay content. A new tool, the litho-density tool (LDT), has been used along with conventional logging tools in a mid-Jurassic sand/shale sequence. The LDT simultaneously measures Pe (effective photoelectric cross-section) and ρa (apparent bulk density). Pe is a function of atomic number which in turn reflects lithology or mineral composition. By using cross-plots derived from the LDT and other logs, patterns of mineral abundance are indicated.
The influence of aluminium on iron oxides: X. properties of Al-substituted goethites
Authors: Schulze D. G. , Schwertmann U. 
Published: December 2006

AbstractFifty-seven goethites, synthesized by a variety of procedures and with Al substitutions of 0–33 mole%, were characterized by XRD, IR, DTA, TEM and chemical techniques. Most of the properties measured showed significant intercorrelations. Mole% Al substitution (measured chemically) did not explain all the relationships among variables, but the inclusion of Δa, defined as the observedadimension minus theadimension predicted by the Vegard rule, explained much of the variation not explained by Al substitution. OH stretching frequency, in particular, was better correlated with Δathan the Al substitution or other properties. The properties of the goethites could best be explained by a combination of Al substitution and structural defects, with Δabeing a measure of the defects. In general, the effect of structural defects was opposite to that of Al substitution. Increase in Al substitution led to a decrease in all three unit-cell dimensions and OH stretching frequency and to an increase in the distance between the two OH bending vibrations (δOH-γOH) and the temperature of dehydroxylation. Increase in structural defects, on the other hand, caused theadimension, Δa, and OH stretching frequency to increase andδOH-γOH and the average temperature of dehydroxylation to decrease. Crystal size tended to decrease with increases in both Al substitution and structural defects. Surface area was significantly correlated with the reciprocal of the mean crystal thickness in theadirection. Comparison of XRD and TEM data showed that many samples consisted of crystals with several coherently scattering domains. The nature of the defects, i.e. whether they occur primarily in the interdomain areas or whether they are also distributed throughout the coherently diffracting domains, could not be determined.
Mode d'empilement des feuillets dans la vermiculite sodique hydratee a une couche (phase a 11·85 Å)
Authors: de la Calle C. , Plançon A. , Pons C. H. , Dubernat J. , Suquet H. , Pezerat H. 
Published: December 2006

ResumeComme la plupart des vermiculites, l'hydrate à une couche de la vermiculite-Na (d001= 11·85 Å) présente une structure semi-ordonnée, avec des défauts d'empilement (glissements selon l'axeb). Le plan (h0l)* du réseau réciproque est entièrement discret, tandis que les rangées n'appartenant pas à ce plan sont plus ou moins diffuses dans la directionc*. La projectionx0zest obtenue par une classique analyse de Fourier bidimensionelle. Dans les plans (0kl)* et (1kl)*, certaines rangées semblent presque discrètes: ceci permet d'essayer de déterminer la translationselon l'axe 0yentre deux feuillets adjacents. Le calcul des intensités des diffusions le long des rangées des plans (0kl)* et (1kl)* conduit à ne retenir qu'un seul modèle. Le désordre résulte d'une distribution aléatoire de trois translations parallèles à l'axe Oy: l'une est nulle et les deux autres sont de +0·307bet −0·307b. Le principal intérêt de ce travail est de présenter une nouvelle méthode d'approche pour l'étude des structures semi-ordonnées.
Hydrothermal clay mineral formation in a biotite-granite in northern Switzerland
Authors: Peters Tj. , Hofmann B. 
Published: December 2006

AbstractClay minerals of several hydrothermally altered zones in a 1200-m biotite-granite core from a drillhole in northern Switzerland were studied microscopically, by XRD and by electron microprobe. The minerals principally affected by the hydrothermal alteration were plagioclase (An5-An20) and, to a lesser extent, biotite. Illite, regularly interstratified illite-smectite and dioctahedral chlorite-smectite, dioctahedral chlorite, trioctahedral chlorite and kaolinite were detected in the alteration products. Commonly, two or more clay minerals occurred together in pseudomorphs after plagioclase. The mineral chemistry of the clay minerals showed a predominance of the substitution KAl for Si and, to a lesser extent, MgSi for Al. Fluid-inclusion data and the absence of pure smectite and epidote indicated temperatures of ∼200°C for the fluid that caused this alteration.
L'‘halloysite’ blanche riche en fer de vate (vanuatu)—hypothese d'un edifice interstratifie halloysite-hisingerit
Authors: Quantin P. , Herbillon A. J. , Janot C. , Siefferman G. 
Published: December 2006

ResumeL'argile blanche en provenance du sol ferrallitique dérivé de matériaux pyroclastiques de Vaté (Vanuatu) possède un rapport moléculaire SiO2/(Al2O3+ Fe2O3) proche de 2, est riche en fer (∼7% Fe2O3) et se présente sous forme de fines lamelles irrégulières et parfois froissées. Sous l'effet de tout traitement de déshydratation, l'espacement basal de cette argile passe progressivement de 10 Å vers 7 Å. Toutes ces caractéristiques permettraient son identification comme halloysite (10 Å) ferrifère hydratée. Cependant, les spectres de diffraction des rayons X de cette argile déshydratée puis déshydroxylée ne correspondent pas à ceux que l'on obtient pour une halloysite ‘normale’. Ils révèlent plutôt la présence d'un édifice interstratifié 1:1/2:1 où le minéral 2:1, présent à raison de 20% environ, est dioctaédrique. En outre, la CEC de ce matériau (∼44 mEq/100 g à pH 4) est anormalement élevée pour un minéral 1:1. Par spectroscopie Mössbauer, on établit que la quasi-totalité du fer présent dans cet échantillon doit être localisée en position octaédrique au sein d'un phyllosilicate. Comme ce fer est ferrique, son inclusion dans la couche octaédrique d'un minéral 1:1 ne pourrait justifier l'importante charge négative permanente que porte cette argile. En réalité, toutes les propriétés reconnues pour ce matériau justifient son identification comme minéral interstratififé de 80% environ d'halloysite et de 20% de smectite ferrifère. Certaines particularités des spectres d'infrarouge, notamment l'absence des bandes à 3560 et 820 cm−1caractéristiques des vibrations d'élongation et de déformation des hydroxyles de la nontronite, suggèrent que la smectite ferrifère inclue dans l'édifice interstratifié pourrait être une hisingérite dioctaédrique.