bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal reactions of leadhillite Pb4SO4(CO3)2(OH)2
Authors: Milodowski A. E. , Morgan D. J.
Published: December 2006

Reactions undergone by leadhillite from the type locality on heating to 1000°C have been followed by DTA, TG, DSC, evolved gas analysis, continuous-heating XRD and IR, and hot-stage microscopy. Intermediate decomposition products were identified by X-ray powder photography. At 80°C, biaxial leadhillite inverts to a uniaxial phase with properties similar to those of susannite, a naturally occurring polymorph of leadhillite, but this higher-temperature modification only partially reverts to the original structure on cooling (up to 24 hours at room temperature is required for complete reversion). Between 250 and 600°C the mineral undergoes two decomposition reactions: PbO.PbCO3 and PbO.PbSO4 form during the first reaction (PbCO3 may form in the initial stages) and 4PbO.PbSO4 during the second. α-2PbO.PbSO4 appears at 650°C due to solid-state reaction between the other lead oxysulphate products. Melting occurs above 850°C. The reaction products are discussed in relation to the phase diagrams for the systems PbO-CO2 and PbO-PbSO4.
Characterization and reducibility of Itakpe and Agbaja (Nigerian) iron ores
Authors: Adedeji F. A. , Sale F. R.
Published: December 2006

Two iron ore samples from Nigeria have been examined using TG, DTA, EGA, XRD, and optical and electron microscopy. Itakpe iron ore is hematite-rich, this mineral being intergrown with magnetite, and silica is the major impurity. Agbaja ore is an acidic oölite ore consisting of goethite and magnetite, with alumina, silica and phosphorus as major impurities. Itakpe is typical of a rich ore formed by magmatic segregation whilst Agbaja is a lean ore of sedimentary origin. Isothermal mass-change measurements in hydrogen and carbon monoxide in the range 800–1100°C show Agbaja to be less reducible than Itakpe; in particular, Agbaja is very irreducible at 1100°C because of sintering of the ore. Characterization and reducibility experiments were also carried out on Corby (Northamptonshire, UK) iron ore for comparison.
Measurement of high-alumina cement-calcium carbonate reactions using DTA
Authors: Midgley H. G.
Published: December 2006

Hydrating high-alumina cement will react with calcium carbonate to form the complex mineral calcium carboaluminate hydrate, 3CaO.Al2O3.CaCO3.12H2O. This mineral is reported to be capable of providing strength in concrete and so may provide an alternative to the minerals normally found in the hydration of high-alumina cement, which may under certain conditions convert to other minerals with a loss in strength. Some doubt has been cast on the stability of calcium carboaluminate hydrate and it has been found that in hydrated high-alumina cement, calcium carboaluminate hydrate decomposes at temperatures in excess of 60°C. Cube compressive strength tests on high-alumina cement and high-alumina cement-calcium carbonate pastes have shown that the latter have a lower strength than pastes made with high-alumina cement alone. When cured at 50°C the high-alumina cement-calcium carbonate pastes show a loss in strength with curing time. Cements made with the high-alumina cement-calcium carbonate mixture always have a lower strength than those made with high-alumina cement alone and so no advantage is gained from their use.
Ordered illite-smectite and kaolinite-smectite: pedogenic minerals in a Lower Carboniferous paleosol sequence, South Wales?
Authors: Robinson D. , Wright V. P.
Published: December 2006

Mixed-layer clay minerals of illite-smectite, having smectite contents ∼25% and IS ordering, kaolinite-smectite, and a three-component variety with kaolinite-smectite-chlorite-like material are described from a Carboniferous paleosol in South Wales. The clays, which are restricted to particular horizons, are unusual occurrences in a pedogenic sediment and pose particular problems as to their genesis. Positive geological evidence, principally in the form of mineralogical and organic thermal maturation data, demonstrates that the rocks of the region cannot have reached diagenetic temperatures > 100°C. This would appear to suggest a pedogenic rather than a diagenetic origin for these clays. In these sediments the only plausible mechanism of illitization to produce the illite-smectite would be by repeated wetting and drying cycles causing irreversible K fixation. Such cycles would be entirely realistic for a vertisol-like paleosol formed on overbank deposits in a floodplain environment subject to strong seasonal moisture contrasts. If this interpretation is correct, this illite-smectite represents the most illitic yet recorded from a non-burial or non-hydrothermal environment.
A contribution to the study of the catalytic action of clays on the polymerization of styrene: I. Characterization of polystyrenes
Authors: Njopwouo D. , Roques G. , Wandji R.
Published: December 2006

Three clay samples (a kaolinite, a halloysite and an inseparable mixture of kaolinite-palygorskite-illite-montmorillonite) were, after a mild pretreatment, successfully tested as catalysts in the polymerization of styrene. The catalytic activity of the clay (measured by the conversion rate), the MW and the colour of the polystyrene obtained depended not only on the chemical composition and the structure of the clay catalyst but also on its concentration in the medium. The polystyrenes obtained on the clay catalyst were composed of two groups of macromolecules, one with low MW and the other with high MW.
Structure et proprietes d'hydratation des nontronites
Authors: Suquet H. , Malard C. , Pezerat H.
Published: December 2006

Les nontronites ne présentent pas les propriétés caractéristiques des phyllosilicates 2:1 magnésiens ou alumineux à substitutions tétraédriques: domaines d'hydratation homogène, isotherme de désorption d'eau avec paliers, organisation structurale ordonnée ou semi-ordonnée. Or les analyses structurales montrent que ce sont des beidellites ferriffères et l'étude de l'effet Hofmann–Klemen confirme le taux très faible de lacunes et de substitutions octaédriques. Diverses hypothèses justifiant ces propriétés sont présentées et discutées.
The acidity of trivalent cation-exchanged montmorillonite. Temperature-Programmed desorption and infrared studies of pyridine and n-butylamine
Authors: Breen C. , Deane A. T. , Flynn J. J.
Published: December 2006

Temperature-programmed desorption (TPD) and IR spectroscopy were used to characterize the number and strength of acid sites in Al3+-, Cr3+- and Fe3+-exchanged montmorillonite. The bases pyridine and n-butylamine occupied three different sites in the interlamellar space: (i) physisorbed base, (ii) base bound to Lewis acid sites, and (iii) protonated base. TPD profiles for pyridine were characterized by maxima at 40°, 150° and 340°C, whilst those for n-butylamine occurred at 30°, 200° and 410°C. The Al3+- and Cr3+-exchanged forms were stable up to pretreatment temperatures of 300°C, but the Fe3+-form required > 3 day exposure to base vapour to re-establish the high-temperature desorption peak. Variable-temperature IR studies showed that the number of Brönsted-bound pyridine molecules increased with increased outgassing temperature.
The adsorption of 1,4-dioxan, tetrahydrofuran and tetrahydropyran from binary solution with methanol on Al3+ and Cr3+-exchanged montmorillonite
Authors: Breen C. , Deane A.
Published: December 2006

Surface excess isotherms were determined for the adsorption of 1,4-dioxan (DIOX), tetrahydropyran (THP) and tetrahydrofuran (THF) from binary solution with methanol (MeOH) on Al3+- and Cr3+-exchanged, montmorillonite containing different amounts of pre-adsorbed water. The isotherm type is dominated by the binary mixture whereas the amplitude, which follows the sequence DIOX > THP > THF, is further influenced by the exchange cation, Al3+ > Cr3+, and the water content of the clay. The sorption of DIOX and THP from MeOH exhibit a type IV isotherm in the Schay-Nagy classification on both cation-exchanged forms, whilst that of THF from MeOH is of type I and THF is the preferred adsorbate. The azeotropic point for the type IV isotherms is close to a 1:1 mole ratio for the samples dried at 120°C but when the samples are rehydrated at 12% r.h. following thermal pretreatment at 120°C the azeotropic point shifts in favour of the cyclic ethers DIOX and THP, making them the preferred component over a substantial portion of the composition range.
Synthesis and crystallogenesis of ferric smectite by evolution of Si-Fe coprecipitates in oxidizing conditions
Authors: Decarreau A. , Bonnin D. , Badaut-Trauth D. , Couty R. , Kaiser P.
Published: December 2006

Silico-ferric coprecipitates, with chemical formula, were aged in suspension at 75°, 100° and 150°C and the structural evolution of solids with time studied by XRD, TEM, and IR, Mössbauer and EXAFS spectroscopy. The initial Si-Fe coprecipitate was found to be amorphous but showed local order similar to that of a smectite layer. At 75°C only a weak structural evolution of the silico-ferric product towards a smectite-like structure was observed. Experiments performed at 100° and 150°C led to synthesis of a ferric smectite with structural formula. During syntheses a highly soluble silico-ferric complex appeared; the Si/Fe atomic ratio of this complex was 3, and the apparent concentration of Fe3+in solution reached 27 mm/l. These syntheses prove that the crystallization of a dioctahedral smectite, containing only Fe3+atoms in the octahedral sheet, is possible under strictly oxidizing conditions. However, crystal growth of a ferric smectite under these conditions is slow and only syntheses carried out at sufficiently high temperatures give convincing results.
Influence of the chemical composition and textural characteristics of palygorskite on the acid leaching of octahedral cations
Authors: Corma A. , Mifsud A. , Sanz E.
Published: December 2006

Leaching of two palygorskites with different octahedral aluminium contents has been carried out in HCl at 20°–70°C. The acid concentration was varied in the range 0·05–6 mol. 1−1, using 4–500 g.g−1 liquid to solid ratios. Acid leaching of up to 60% of the octahedral cations did not provoke structural changes or amorphization of the samples. On the bases of the selectivity of extraction of Mg2+, Fe3+ and Al3+, it appeared that most of the octahedral edge positions are occupied by Mg2+, some by Fe3+, and practically none by Al3+. Differences in acid-leaching behaviour between the two palygorskites was better related to accessible surface than chemical composition.
Electron spin resonance studies of halloysites
Authors: Chaikum N. , Carr R. M.
Published: December 2006

Absorption lines in the g ∼ 4 region of ESR spectra of three New Zealand halloysites were found to originate from similar paramagnetic centres as in kaolinites. Resonances in the g ∼ 4 region were not common to all the halloysites, although the signal at g = 2·0 for the Matauri Bay halloysite is probably due to a trapped positive hole or trapped ion. A 6-line resonance produced by Te Puke halloysite and removable by Na-saturation is attributed to exchangeable Mn on the clay surface. Low-temperature lines exhibited by all samples are due to V4+ or VO2+ replacing Al3+ in the octahedral sheet.
Caracteristiques structurales d'une smectite dioctaedrique en fonction de l'ordre-desordre dans la distribution des charges electriques: I. Etudes des reflexions 00l
Authors: Ben Hadj-Amara A. , Besson G. , Tchoubar C.
Published: December 2006

Resume

Hofmann & Klemen ont observé qu'en chauffant modérément (200-220°C) une smectite dioctaèdrique à substitutions octaàdriques saturée par du lithium, celle-ci perdait sa capacité d'échange cationique et son pouvoir de solvatation. Les auteurs ont attribué cet effet à la migration des cations Li vers la couche octaèdrique. Nous avons, en utilisant essentiellement la diffraction X aux grands angles et la microscopie électronique, caractérisé de manière quantitative la structure d'une smectite à déficit de charge mixte (c'est-à.-dire ayant 30% de substitutions dans les couches téraèdriques et 70% dans les couches octaèdriques) saturée par du nickel, avant et après chauffage. Nous avons ainsi pu montrer en éudiant les réflexions 00l qu'après un chauffage à 400°C, les cations interfoliaires migrent vers la cavité octaèdrique vacante pour compenser la totalité des charges négatives dues aux substitutions Al → Mg et qu'il existe une distribution inhomogène de la charge entre les couches octaèdriques et tétraèdriques au sein d'un même cristal. Certains feuillets ont des substitutions uniquement dans la couche octaèdrique, d'autres uniquement dans la couche tétraèdrique, et toutes les possibilités peuvent exister entre ces deux pôles extrèmes.
Clay mineral sources of the Grenada Basin, Southeastern Caribbean
Authors: Gandais V.
Published: December 2006

This study of the Quaternary clay sedimentation in the Grenada Basin (Southeastern Caribbean) is based on six cores raised from depths of 1800 to 3000 m. Mineralogical analysis of <2µm and <0·3µm fractions revealed the presence of a four-component association — smectites, illite, kaolinite and chlorite — in which smectites were always dominant. These minerals were derived from two sources: the Lesser Antilles Arc, which contributed only smectites and kaolinite, and the South American continent, where smectites, kaolinite, chlorite and illite coexist. Geochemical data indicate that Ba and Cr are specific indicators of the South American minerals, whereas Cu characterizes the Antillean clays. The South American contribution, now prevailing, was less important during the Sangamon. The Antillean contribution was episodically predominant during the Wisconsin.
Magnetite in soils: I. The synthesis of single-domain and superparamagnetic magnetite
Authors: Taylor R. M. , Maher B. A. , Self P. G.
Published: December 2006

A series of experiments has been carried out to investigate the possible formation of magnetite, Fe3O4, under ambient soil-forming conditions. Rapid and easy synthesis of magnetite was achieved through controlled oxidation of Fe2+solutions at room temperatures and near neutral pH values. The synthetic products were found to range in size between 0·01–0·07µm (mean diameter) and hence span the theoretical superparamagnetic-single-domain grain-size boundary.
Magnetic properties and site occupancy of iron in nontronite
Authors: Lear P. R. , Stucki J. W.
Published: December 2006

The magnetic susceptibilities of seven different nontronites in their natural oxidation states were measured between 5 and 100 K. Results revealed that the magnetic exchange interaction in all samples was antiferromagnetic, except no clear minimum occurred at the Néel temperature. Possible explanations for this phenomenon which are discussed include magnetic dilution due to isomorphous substitution, and antiferromagnetic frustration due to either non-centrosymmetric distribution of octahedral Fe3+or tetrahedral Fe3+substitution. A computer simulation model was developed to demonstrate the effects of these variables on long-range magnetic ordering. Magnetic dilution and tetrahedral Fe3+content could explain the anomalous antiferromagnetic behaviour in some, but not all, samples. The non-centrosymmetric model is the only one which explains the behaviour of all samples. In this model, at least 13% of the octahedral Fe3+would occupytrans-dihydroxide sites, with the balance incissites. Magnetic frustration occurs because two Fe3+neighbours of a third Fe3+ion are also neighbours to each other, making the simultaneous satisfaction of all antiferromagnetic exchange interactions impossible.
EPR of VO2+ ions in Al-pillared montmorillonite
Authors: Braddell O. , Barklie R. C. , Doff D. H.
Published: December 2006

A pillared smectite clay has been formed by treating Na-montmorillonite with a hydroxy-aluminium solution with an OH/Al ratio of two. Heating the pillared clay for four h at 500°C reduces the interlayer spacing, measured at ambient humidity, from ∼ 9·4 to 8·0 Å. Hydrated VO2+ (and Mg2+) ions have been introduced into the region between the pillars by immersing the pillared clay in VOSO4-MgCl2 solutions and EPR measurements show that in general both immobile and mobile VO2+ ions are present. The immobile ion is probably VO2+(OH)x(H2O)5·x where x = 2–4, and is adsorbed on the pillars with a concentration that saturates at about 1 per 8 Al13 pillars in the unfired clay, and 1 per 4·3 pillars in the fired clay. The mobile species is VO2+(H2O)5 and for both fired and unfired clay in the wet state at room temperature it has a rotational correlation time of (9 ± 1) × 10−11s rad−1.
Weathering of biotite into dioctahedral clay minerals
Authors: Fordham A. W.
Published: December 2006

Changes which occur during the natural weathering of biotite in granite gneiss and associated soils are measured by microanalysis and illustrated by SEM. Biotite weathers through a series of interstratified minerals to vermiculite and/or smectite phases which decompose rapidly to kaolinite. Both vermiculite and smectite phases appear to be dioctahedral, on the basis of chemical compositions derived from microprobe data. Weathering products are first apparent on the edges of laminae, where interstratified minerals are formed at right angles to both the edge face and the cleavage. Weathering soon develops along cleavage planes, initially most strongly near the edges of flakes, but then permeating extensively into the body of flakes and subdivided segments. The orientation of interstratified minerals and kaolinite within cleavages is parallel to the cleavage.
Crystallochemical classifications of phyllosilicates based on the unified system of projection of chemical composition: I. The mica group
Authors: Wiewióra A.
Published: December 2006

A unified system of vector representation of chemical composition is proposed for the phyllosilicates based on projection of the composition, as given by crystallochemical formula, onto a field with orthogonal axes chosen for octahedral divalent cations, R2+, and Si (X, Y, respectively), and oblique axes for octahedral trivalent cations, R3+, and vacancies, □, (V, Z, respectively). Point coordinates for each set of axes were used to define the direction and length of the unit vectors for phyllosilicates belonging to different groups. Parallel to these fundamental directions the composition isolines were drawn in the projection fields. Applied to micas, this system enables control of the chemical composition by the general crystallochemical formula covering all varieties of Li-free dioctahedral and trioctahedral micas:

where z (number of vacancies) = (y-x+ m)/2; m (layer charge) =1; u+y+z = 3. There is a similar formula for vacancy-free lithian micas:

where w = m — x+y;m=1; u+y+w = 3, and for Li-free brittle micas:

where z = (y — x+m)/2; m = 2; u+y+z = 3. Projection fields were used to classify micas.
Crystallochemical classifications of phyllosilicates based on the unified system of projection of chemical composition: III. The serpentine-kaolin group
Authors: Wiewióra A.
Published: December 2006

A unified system of projection of chemical composition, prepared initially for micas and chlorites, has been applied to minerals of the serpentine-kaolinite group. It has been shown that the chemical composition in the projection field is controlled by the formula, the unit of which is: (Si(2-x)Alx)O5(OH)4, where u+y+z=3, z=y-x. Using projection fields for different chemical systems it has been shown that among the most important end-members are kaolinite minerals, true serpentines, berthierine, brindleyite, amesite, cronstedtite, greenalite, nepouite and their analogues having different substitutions in the octahedral sheets.
Hydrothermal (200°C) synthesis and crystal chemistry of iron-rich kaolinites
Authors: Petit S. , Decarreau A.
Published: December 2006

In order to study Al-Fe substitution, Fe-kaolinites were synthesized at 200°C from glasses (Si/(Al + Fe) = 1) with varying Fe content. XRD and IR spectroscopy showed that kaolinites with increasing Fe contents could be synthesized, and Mössbauer spectroscopy indicated that the iron is strictly ferric. Chemical analyses (STEM) of kaolinite particles determined up to almost 7% Fe2O3, which probably does not represent a structural limit. The effect of Fe3+ content is evident on growth kinetics and particle size of kaolinites, both decreasing with % Fe2O3. However, it is not possible to establish a general correlation between Fe content and percentage of structural defects. Acccording to IR spectroscopy, some synthesized Fe-rich kaolinites can have relatively good crystallinity.
Dissolution kinetics of sepiolite from Eskisehir (Turkey) in hydrochloric and nitric acids
Authors: Cetisli H. , Gedikbey T.
Published: December 2006

Dissolution kinetics of sepiolite from Eskisehir (Turkey) have been investigated at various temperatures and particle sizes using dilute hydrochloric and nitric acids. Dissolution reaction rate constants were calculated and apparent activation energies were dependent on acid concentration. For both acids, apparent activation energy values reached a minimum of ∼11 kcal/mol at an acid concentration of 0·75 M. For the second-order reaction which is independent of the acid concentration, the activation energy was 14·5 kcal/mol for both acids. The reaction rate constants were proportional to the acid concentrations, and inversely proportional to the square-root of the initial particle radii of the sepiolite.
Etude de la repartition de l'eau dans des argiles saturees Mg2+ aux fortes teneurs en eau
Authors: Touret O. , Pons C. H. , Tessier D. , Tardy Y.
Published: December 2006

Powdered 2:1 Mg-clay samples were rehydrated up to the maximum hydration. Both scanning and transmission electron microscopy were used to characterize their structural organization i.e. particle arrangement, texture and crystal structure. Low-angle X-ray scattering experiments were carried out to quantify the microstructure of the system. The results showed that sample water contents reached at saturation are not directly related to changes in layer distance. The hydration mechanism is rather correlated to particle size and particle aggregate size. It is also shown that the a, b plane extension of the layers influences particle size and shape. Finally, it appears that for a better understanding of clay swelling mechanisms, at high water contents, it is necessary to take into account all organization levels and that the contribution of interlayer space to the total water content, for Mg-smectites, is small.
An expert system for the structural characterization of kaolinites
Authors: Plançon A. , Zacharie C.
Published: December 2006

Until recently, the determination of the defect structures (previously referred to incorrectly as “crystallinity”) of kaolinites has been obtained in one of two ways: (1) measurement of the Hinckley index, or (2) by comparing calculated X-ray diffraction patterns based on a model of the defect structure (including types of defects and abundances) with experimental diffraction profiles. The Hinckley method is simple and easy to perform but contains no real information about the defect structure. Calculated XRD patterns are based on real defects but these calculations are time consuming and require some skill in application. Another approach is proposed: an expert system which will accurately describe the defect structure of kaolinites based on a few measurements taken from a normal powder diffraction profile. This system has been verified for nine kaolinite samples for which the defect structure was previously determined by comparison of calculated and observed diffraction profiles. The expert system reproduced the correct defect structure for each of the samples.
Electron paramagnetic resonance study of non-exchangeable vanadium(IV) in rectorites
Authors: Goodman B. A. , Nadeau P. H.
Published: December 2006

EPR spectroscopy was used to provide evidence for the existence of vanadium(IV) in two samples of rectorite. Possible sites for the vanadium are the tetrahedral and octahedral sites in the 2:1 layers and the non-exchangeable interlayer sites in the paragonite part of the structure. Consideration is given to each of these possibilities but the experimental evidence is insufficient to identify conclusively the location of the vanadium. Since substantial amounts of vanadium(IV) were present in the only well-defined rectorite samples obtainable, it is possible that the formation of rectorite is facilitated by the presence of vanadium.
A Mössbauer study of green rust precipitates: I. Preparations from sulphate solutions
Authors: Cuttler A. H. , Man V. , Cranshaw T. E. , Longworth G.
Published: December 2006

The preparation of green rusts from sulphate solutions and representative Mössbauer spectra are described. As the samples oxidized readily, attention focused on the Mössbauer parameters at liquid nitrogen and helium temperatures. The spectra recorded at 77 K could be fitted satisfactorily with one ferrous iron quadrupole doublet with a separation of 2·93 mms−1 and one ferric iron quadrupole doublet with a separation of 0·45 mms−1. In some spectra a ferric iron magnetic hyperfine of strength 49·2 T was also apparent. At 4·2 K, the ferrous iron exhibited a hyperfine splitting with a field of 12·4 T whilst the ferric iron exhibited a hyperfine splitting with a field of strength 50·4 T. The ratio of ferrous to ferric ions was 2·25 ± 0·25 at 77 K and at 4·2 K, and ∼1·6 with a large variation at room temperature. The liquid helium spectra did not always give a good chi-squared fit, the main reason being attributed to relaxation. The line-width of the ferrous iron site at 77 K is slightly larger than that for iron metal and could be explained by a variation in the number of near Fe3+ neighbours at different Fe2+ sites, consistent with the assumption that the ferrous iron site is in the hydroxide sheet. The effect of different numbers of Fe2+ and Fe3+ neighbours probably contributed to the increase in line-widths at 4·2 K compared with those at 77 K. The ferrous iron doublet is marginally different to those of chloride and hydroxy-carbonate green rusts and the aluminium analogues.
Les complexes montmorillonite-Cu(III)-benzène: une contribution
Authors: Walter D. , Saehr D. , Wey R.
Published: December 2006

Des montmorillonites cuivriques ont été exposées à des vapeurs de benzène, au cours de cycles de déshydratation, adsorption, désorption de l'excès et réhydratation. La fixation du benzène et sa transformation dans les espaces interfoliaires ont été suivies au moyen d'analyses thermogravimétriques, radiocristallographiques et spectrophotométriques infrarouges. Celles-ci ont permis de mettre en évidence deux réactions, correspondant l'une à l'adsorption d'une molécule de benzène par ion Cu2+, l'autre à trois molécules de benzène. Ce dernier se polymérise dans les espaces interfoliaires avec formation tout d'abord de poly (p-phénylène) puis d'un composé qui pourrait s'apparenter à du graphite.
Berthierine from the non-marine Wealden (Early Cretaceous) sediments of south-east England
Authors: Taylor K. G.
Published: December 2006

A thin (15–20 cm) Fe-rich intraformational conglomerate in the fresh- to brackish-water Early Cretaceous succession of south-east England contains pisoids and pseudo-ooids of a green clay mineral which has been identified as berthierine. The pisoids (up to 0·5 cm in size) are concentrically laminated, have complex structure, and are frequently nucleated around a sandstone fragment. They show evidence of weathering due to a change in their environment after formation. The ooids have well to moderately well developed concentric lamination, are very often multi-nucleated and do not always completely cover the nucleus. They suggest formation as a result of mineral precipitation as opposed to agitation and accretion. The climate and environment during the Wealden were suited to the formation of Fe-rich soils and it is likely that the pisoids and ooids were originally composed of iron oxyhydroxide and kaolinite, having formed in soil in the Weald Basin. They were then eroded and deposited in the base of a large scour structure as part of the conglomerate. On burial, and the attainment of low Eh conditions, berthierine formed by diagenetic transformation of the pre-existing minerals.
Impact of clay particle orientation on quantitative clay diffractometry
Authors: Zevin L. , Viaene W.
Published: December 2006

Preferred orientation of clay particles in various clay mounts was measured with an X-ray texture diffractometer. Pole distributions are approximately symmetrical about the normal to the sample. Particle orientation is characterized by standard deviations ranging from 7° for thin sedimented layers, to 20° and more for dry-pressed samples, the latter showing less dependence on particle size. The orientation of the reflecting particles may span a considerable angular range affecting the intensities of diffraction peaks observed on contemporary powder diffractometers, even those with moderate axial divergence. A theory based on the diffractometer geometry was developed to calculate the effect of particle orientation. Results are presented as modified Lorentz factors for orientations deduced from experimental observations. In qualitative X-ray diffractometry of clays, preference must be given to preparation techniques which ensure a high degree of preferred orientation and therefore strong enhancement of basal reflections. In quantitative X-ray diffractometry, the main factor is the reproducibility of particle orientation, and suction and dry pressing are promising methods of sample preparation.
The I-S contact in 10 Å-17 Å interstratified clay minerals
Authors: Tettenhorst R. T. , Corbató C. E. , Haller R. I.
Published: December 2006

Calculated X-ray diffraction profiles of 10 Å-17 Å interstratified clay minerals, which make allowance for fundamental illite particles, confirm many of the inferences made in a previous analysis by Corbató & Tettenhorst (1987). However, some of these profiles do not appear to match well with patterns obtained from real interstratified clay minerals. The lack of agreement is apparently a consequence of the assumption that the interlayer spacing formed at the contact of I and S (illite and smectite) silicate layers is exclusively 17 Å. The results suggest that this interlayer spacing may be either 10 Å or 17 Å.
Sorption of water vapour by M-montmorillonite (M = Na, Li, La)
Authors: Trillo J. M. , Poyato J. , Tobías M. M. , Castro M. A.
Published: December 2006

The effect of heating on the water sorption capacity of a La-saturated montmorillonite, La-Mt, has been investigated. Sodium and Li as exchangeable ions have also been included for comparative purposes. XPS of La-Mt shows no migration of La(III) from interlamellar positions to octahedral sites on heating at 300°C. The water adsorbed as a multilayer on the external surface of the montmorillonite has been subtracted from the total sorbed water. Although the c-spacing of La-Mt corresponds to a two-layer hydrate, in the relative humidity range from 30 to 70%, the interlamellar water amounts to only 70% of the value for a complete monolayer. Heating at 300°C for 24 h has no influence on the uptake of molecular water between the structural layers of the La-Mt. The average numbers of water molecules per exchangeable ion sorbed into the interlamellar spacing up to 50% r.h. are: 5(Na-Mt), 3(Li-Mt) and 13(La-Mt).
Clay mineral distribution and provenance in Mesozoic and Tertiary mudrocks of the Moray Firth and northern North Sea
Authors: Pearson M. J.
Published: December 2006

Clay mineral abundances in Mesozoic and Tertiary argillaceous strata from 15 exploration wells in the Inner and Outer Moray Firth, Viking Graben and East Shetland Basins of the northern North Sea have been determined in <0·2 µm fractions of cuttings samples. The clay assemblages of more deeply-buried samples cannot be unambiguously related to sedimentary input because of the diagenetic overprint which may account for much of the chlorite and related interstratified minerals. Other sediments, discussed on a regional basis and related to the geological history of the basins, are interpreted in terms of clay mineral provenance and control by climate, tectonic and volcanic activity. The distribution of illite-smectite can often be related to volcanic activity both in the Forties area during the M. Jurassic, and on the NE Atlantic continental margin during the U. Cretaceous-Early Tertiary which affected the North Sea more widely and left a prominent record in the Viking Graben and East Shetland Basin. Kaolinite associated with lignite-bearing sediments in the Outer Moray Firth Basin was probably derived by alteration of volcanic material in lagoonal or deltaic environments. Some U. Jurassic and L. Cretaceous sediments of the Inner Moray Basin are rich in illite-smectite, the origin of which is not clear.
Expert System for Structural Characterization of Phyllosilicates: II. Application to Mixed-Layer Minerals
Authors: Drits V. A. , Plançon A.
Published: December 2006

The expert system described in the first part of this paper has been applied to the identification of mixed-layer phyllosilicates (mica-smectite, mica-vermiculite, chlorite-smectite, chlorite-vermiculite, chlorite-swelling chlorite, chlorite-mica, chlorite-talc, kaolinite-smectite, talc-smectite), and to the determination of their structural parameters (Reichweite, R, and proportions of constituting layers, Wi). The expert system has been run utilizing the data extracted from (1) experimental XRD patterns for which structural parameters had been evaluated by comparison with calculated patterns, or (2) patterns calculated using pre-selected values of the structural parameters. In all cases examined, the expert system provided correct conclusions concerning the identification of a mixed-layer phyllosilicate and the value of the Reichweite, while the abundances of the component layers were evaluated with a margin of error usually <5%.
Saponite, Corrensite and Chlorite-Saponite Mixed-Layers in the Sancerre-Couy Deep Drill-Hole (France)
Authors: Beaufort D. , Meunier A.
Published: December 2006

The clay deposits in fractures of the metamorphic basement under the Paris Basin sedimentary formations at Sancerre-Couy (France) are composed of trioctahedral species which are exceptionally well crystallized. Three samples were chosen in order to study the chemical composition of 100% expandable saponite, 50% expandable corrensite and 10% expandable chlorite-saponite mixed-layer mineral C90–S10 Two sets of microchemical analyses were performed in order to determine the variations of the composition on large and small numbers of particles. X-ray diffraction (XRD) and Mössbauer spectrometry were performed on purified samples.

The mathematical decomposition of Si, Al and Mg histograms established from microanalyses of a large number of crystals of saponite, corrensite and C90–S10 evidences bimodal populations. The total Fe content of the three species is unimodal whatever the chemical composition of the surrounding rock and the Fe2+/Fe3+ ratio. The structural formulae established from a large number of microanalyses of a few particles show that there are no parental relationships between saponite, corrensite and C90–S10. The expandable layer of corrensite is characterized by a high charge. It is proposed that the tetrahedral sheets adjacent to the brucitic sheet and the exchangeable interlayer in a 2 : 1 unit are identical in corrensite.
The Formation of Green Rust and Its Transformation to Lepidocrocite
Authors: Schwertmann U. , Fechter H.
Published: December 2006

The formation of FeII,III hydoxy salts (green rusts) from FeII sulphate and chloride solutions and their transformation to lepidocrocite, γ-FeOOH, was studied at ambient temperature, constant pH of ∼7.0 and under controlled air flow. The formation of green rust and its subsequent transformation to lepidocrocite could be distinguished by the reaction rate and solution chemistry. The SO42− and Cl− concentrations in solution attain a minimum at the break between the two reaction steps and are completely restored to their initial values after complete transformation to lepidocrocite. While the green rust is being formed, its FeII/FeIII ratio shows a minor decrease and its FeIII/anion ratio a minor increase. These ratios, however, deviate from the ideal pyroaurite-type structure (M2+/M3+ = 3; M3+/A− = 1; M: metal; A−: anion) and possibilities to accommodate this deviation are discussed. A period during which no protons were produced (i.e. no base consumed) was found to separate the two reactions in the chloride, but not in the sulphate system. During this period a partial solid state oxidation of the green rust took place, leading to its destabilization and eventual decomposition.
Diagenetic Development of Clay and Related Minerals in Deep Water Sandstones (S. Spain): Evidence of Lithological Control
Authors: Ruiz Cruz M. D.
Published: December 2006

The turbiditic facies of the Aquitanian-Oligocene of the Algeciras and Bolonia Units consist of lutitic-marly beds alternating with varied sandstones. Early diagenetic processes and the development of secondary porosity in sandstones were controlled largely by sedimentary facies. Mineral dissolution processes were important in rocks with high primary porosity (quartzose sandstones) and led to the development of allophane and kaolinite/dickite in later diagenetic stages. In rocks with high contents of biotitic matrix, chlorites and iron oxides were produced, together with the development of secondary porosity. In feldspathic sandstones, the early diagenetic processes produced chlorite, illite, illite-smectite mixed-layers and smaller amounts of kaolinite. In calcareous sandstones, the presence of an early cement prevented, to a certain extent, the dissolution of unstable fragments and restricted the development of clay minerals. The movement of fluids was not important during this early diagenetic stage in controlling the variety or abundance of mineral cements; the controlling factors were the different chemical conditions developed in the pore-solution of the various sandstone types. In spite of similar sandstone burial conditions, the different sandstone lithologies continued to determine the diagenetic processes, especially the degrees of compaction and dissolution. Certain burial processes are common to all levels: the development of reducing conditions is indicated by the development of Fe and Mn carbonates, Fe-dolomites and Fe-chlorites. A later alkaline diagenetic phase was responsible for the development of calcite, feldspar and illite. The circulation of fluids in these stages remained limited, although there was probably some movement from the lutitic-level fluids to the overlying sandstones.
Spectroscopic Study of the Adsorption of Rhodamine 6G on Laponite B for Low Loadings
Authors: Tapia Estévez M. J. , López Arbeloa F. , López Arbeloa T. , López Arbeloa I. , Schoonheydt R. A.
Published: December 2006

The adsorption of Rhodamine 6G in aqueous suspension on Laponite B was investigated by electronic absorption and emission spectroscopies. Fluorescence spectra suggest that the monomer is adsorbed at two different surfaces, the external and the internal. A monomer is intercalated in the interlamellar space at low loading of dye (<3% CEC), whereas the monomeric state of the dye seems to be at the solid-aqueous interface in suspensions with high loading (>12% CEC). The metachromatic effect observed in the absorption spectra, for the loading interval between 1% and 15% CEC of Laponite B, is attributed to the dimerization of the dye, which seems, from X-ray diffraction measurements, to be formed at the clay interlayer. The formation constant and the absorption spectrum of the aggregate were obtained and the dimer was structurally characterized by applying the Exciton Theory. The observed fluorescence quenching for loadings lower than 15% CEC is attributed to energy transfer from monomer to the dimer, which obeys the Perrin model.
Physicochemical and Catalytic Properties of a Modified Natural Clinoptilolite
Authors: Arcoya A. , González J. A. , Travieso N. , Seoane X. L.
Published: December 2006

Samples of natural clinoptilolite modified by treatment with NH4Cl or HCl solutions, followed by thermal treatments, have been characterized, and their catalytic activity evaluated, in o-xylene isomerization and ethanol dehydration reactions. The substitution of the compensating cations by NH4+ does not produce structural changes in the original material, but it opens the channels and increases its acidity and thermal stability. The treatment with HCl increases both the acidity and the effective diameter of the channels and pores but it produces an important loss of zeolite phase. Calcination of the acidic forms above 973 K leads to the breakdown of the zeolite structure. Catalytic activity of the samples is related to the surface acidity. For the original and NH4Cl-treated samples, however, the conversion of o-xylene is limited by the access of the reactant inside the channels of the zeolite. A comparative study with modified sepiolite in dehydration of ethanol has also been performed.
The Progression from Optical Light Microscopy to Transmission Electron Microscopy in the Study of Soils
Authors: Van Oort F. , Jongmans A. G. , Jaunet A. M.
Published: December 2006

The use of electron microscopy to study clay microfabrics in thin-sections is discussed. A technique is described to isolate undisturbed microparts of pedofeatures from thin-sections, which are subsequently used for TEM analysis. Re-embedding with a polyester resin of undisturbed, in situ, neoformed clay microfabrics, obtained by microdrilling and preparation of ultrathin sections by microtoming with a diamond knife are emphasized; these steps enable micromorphology, clay mineralogy, microchemical and HRTEM analysis to be performed on one unique microsample of clay fabrics, with conserved micro-organization. Two examples on clay neoformation are presented to demonstrate that this technique can successfully be applied to unravel the impact of mineral alteration and clay neoformation in undisturbed soil samples on a micro- and a nanometer scale.
Aluminium coordination and structural disorder in halloysite and kaolinite by 27Al NMR spectroscopy
Authors: Newman R.H. , Childs C.W. , Churchman G.J.
Published: December 2006

It has been suggested that interlayer water in halloysite is due to the presence of hydrated cations that balance the negative layer charge produced by Al for Si substitution. To find evidence of 4-coordinate Al (Al(IV)), we investigated six halloysites and two kaolinites using ‘high-field’ and ‘medium-field’ solid-state 27Al MAS NMR spectroscopy. We found Al(IV) in both kaolinite and five halloysite samples, but the contents are all <1% and provide no basis for distinguishing between kaolinite and halloysite. Therefore, the presence of interlayer water in halloysite cannot be attributed to Al for Si substitution. There are, however, signals, tentatively assigned to A1(V), present in the kaolinite spectra but not in the halloysite spectra. The shapes of the low-frequency ‘tails’ of Al(VI) signals in medium-field NMR vary from sample to sample. We interpret this variation in terms of a ‘crystallinity index’. Disorder in kaolinite appears to be primarily the result of Al-vacancy displacements in the octahedral sheet. The NMR crystallinity indices correlate with those from IRS and DTA but not with those from XRD.
A reassessment of the 29Si MAS-NMR spectra of sepiolite and aluminated sepiolite
Authors: D'Espinose de la Caillerie J.-B. , Fripiat J. J.
Published: December 2006

A 29Si MAS-NMR one-pulse and ﹛1H﹜ CP comparative study of sepiolite, folded sepiolite, aluminated sepiolite, and palygorskite was conducted. The three main resonances of sepiolite at -92.0 ± 0.1, —94.3 + 0.1, and — 97.8 ± 0.1 p.p.m. were assigned with respect to the position of the Si atoms within the three pairs of symmetrical sites in the basal plane. The line at —97.8 p.p.m. was attributed to the central sites by comparison with the resonances and chemical environments of Si in talc and palygorskite. The line at —94.3 p.p.m. was attributed to the edge sites, because it is strongly reinforced by cross-polarization. Alumination of sepiolite led to a broadening of the peaks and new downfield resonances in line with what can be observed in other phyllosilicates and zeolites.
Infrared study of octahedral site populations in smectites
Authors: Madejová J. , Komadel P. , Číčel B.
Published: December 2006

The hydroxyl stretching region of two montmorillonites (SWy-1, Crook County, Wyoming, USA, and JP, Jelšový Potok, Slovakia) and a ferruginous smectite (SWa-1, Grant County, Washington, USA) have been analysed using decomposition and curve-fitting. The positions and integrated intensities of component bands were correlated with the nearest cationic environment of the OH groups, and the populations of the octahedral sheet were calculated. The differences between the octahedral coefficients obtained and those from chemical analyses were 0.07 or less. This method provides reasonable contents of octahedral cations for the smectites with various iron contents, containing no other admixtures absorbing in the 3700-3500 cm–1 region. The cation distribution was found to be not completely disordered. Though some preferential pairing has been observed, no general rule could be established.
Stability constants for silicate adsorbed to ferrihydrite
Authors: Hansen H. C. B. , Wetche T. P. , Raulund-Rasmussen K. , Borggaard O. K.
Published: December 2006

Intrinsic surface acidity constants (Kalintr, Ka2intr) and surface complexation constant for adsorption of orthosilicate onto synthetic ferrihydrite (Ksi for the complex ≡FeOSi(OH)3) have been determined from acid/base titrations in 0.001-0.1 M NaClO4 electrolytes and silicate adsorption experiments in 0.01 M NaNOi electrolyte (pH 3-6). The surface equilibrium constants were calculated according to the two-layer model by Dzombak ' Morel (1990). Near equilibrium between protons/hydroxyls in solution and the ferrihydrite surface was obtained within minutes while equilibration with silicate required days-weeks, both reactions probably being diffusion controlled. Applying the values for specific surface area and site densities for ferrihydrite used by Dzombak ' Morel (1990) (600 m2 g–1, 3.4 μmole m–2) the constants pKalintr = 6.93 ± 0.12, pKa2intr = 8.72 ± 0.17 and log Ksi = 3.62 were calculated by using the FITEQL optimization routine. Use of the specific surface area actually measured (269 m2 g-1) gave a poorer fit of the experimental data. Due to the slow adsorption of silicate and hence long shaking times, changes in the surface characteristics of the ferrihydrite seem to take place, probably a decrease in the concentration of surface sites. Adsorption isotherms calculated using the derived equilibrium constants showed that approximately twice the amount of silicate was adsorbed at pH 5 compared with pH 3.

Infrared spectroscopy of silica adsorbed to ferrihydrite showed Si-O stretching absorption maxima in the range 940-960 cm-1. The shift of the absorption maximum to higher wavenumbers with increasing amount of silicate adsorbed is probably due to an increase in the frequency of Si-O-Si bonds between orthosilicate adsorbed at adjacent sites. Small amounts of goethite were identified in the adsorption products.