bluuebunny/crossref_metadata_2025_split huggingface dataset:
Abundance of halloysite neoformation in soils developed from crystalline rocks. Contribution of transmission electron microscopy
Authors: Romero R. , Robert M. , Elsass F. , Garcia C. 
Published: November 2006

AbstractThe soils developed from crystalline and metamorphic rocks in Galicia (NW Spain), are characterized by high concentrations of 1 : 1 phyllosilicates and gels. Thermal analyses, X-ray diffraction after formamide treatment, and IR spectroscopy in the OH vibration range have been performed on the clay fractions, but do not discriminate clearly between the different associated mineralogical phases. HRTEM studies linked with microdiffraction and microanalyses have led to the identification of several types of gel which transform into goethite, gibbsite, clay precursors, and/ or halloysite according to their composition (Fe, Al or Si-Al). Halloysite-like minerals are the main constituents and they have a great variety of morphologies: lamellar, spheroidal, tubular, platy or poikilitic. In general, halloysite and gel formation on crystalline rocks is related to the bioclimatic conditions, involving high hydrolysis in the presence of organic matter. This halloysite seems to be a metastable mineral which would evolve into kaolinite with increasing weathering time.
Adsorption of methylene blue on sepiolite gels: spectroscopic and rheological studies
Authors: Aznar A. J. , Casal B. , Ruiz-Hitzky E. , Lopez-Arbeloa I. , Lopez-Arbeloa F. , Santaren J. , Alvarez A. 
Published: November 2006

AbstractThe adsorption isotherm of methylene blue (MB) on sepiolite gels is of the Langmuir type, indicating a great affinity of the MB towards the sepiolite; the adsorption is quantitative up to adsorption of MB of 0·1 mmol/g sepiolite. The differences observed in the absorption spectrum in the region 500–650 nm for different MB loadings are interpreted in terms of aggregation of MB molecules on the sepiolite surface with the formation of MB dimers, trimers and higher aggregates. The progressive coverage of the sepiolite surface by MB produces a sharp decrease in the viscosity of the gels, and the suspension becomes peptized for an MB loading of 0·21 mmol/g which corresponds to the adsorption of MB dimers. These results indicate that MB avoids particle-to-particle interactions. The viscosity decrease is parallel to the perturbation of the Si-OH groups on the sepiolite surface as observed by IR spectroscopy, suggesting that these silanol groups can also play an important role in the rheological behaviour of aqueous sepiolite dispersions.
The conversion of montmorillonite to interstratified halloysite-smectite by weathering in the Omi acid clay deposit, Japan
Authors: Watanabe T. , Sawada Y. , Russell J. D. , McHardy W. J. , Wilson M. J. 
Published: November 2006

AbstractThe weathering of montmorillonite in the acid clay deposit at Itoigawa, Japan has been investigated by X-ray diffraction (XRD), infrared spectroscopy (IR) and scanning electron microscopy (SEM). In the lower, least weathered part of the deposit, weathering has occurred by the formation of minor amounts of halloysite with concomitant precipitation of a silica phase identified as opal C-T. A relatively rapid transition occurs to the most weathered, upper part of the deposit where the mineralogy is dominated by interstratified halloysite-smectite. Computer simulations of XRD profiles indicate that the interstratified arrangement is random with a probable composition of 70% halloysite and 30% smectite, a composition supported by the 75–85% and 15–25% of the phases, respectively, calculated from the IR spectra.
Weathering of biotite to vermiculite in Quaternary lahars from Monti Ernici, Central Italy
Authors: Pozzuoli A. , Vila E. , Franco E. , Ruiz-Amil A. , De La Calle C. 
Published: November 2006

AbstractThe weathering of biotite in Quaternary lahars from Monti Ernici (Central Italy) via interstratification stages has been studied by X-ray diffraction of both the interstratified minerals and the initial (biotite) and final (vermiculite) end-members. The structure of the biotite and vermiculite is described by means of monodimensional Fourier series. The interstratified phases have been studied using the INTER program which permits an analysis of two interstratified components by Fourier transform methods. It is shown that in the alteration range for biotite to vermiculite even small samples have different spatial concentrations of biotite, vermiculite and an intermediate biotite-vermiculite-type phase. Hydrobiotite and a rare biotite-hydrobiotite with a tendency to regularity have also been documented. Chemically, the process involves considerable oxidation of Fe2+ and the removal of most of the elements, corresponding to a 34% loss in matter. The sequence of the element losses is: K+ > Fe2+ > F− > Mn2+ > Si4+ > Mg2+ > Al3+ > Ti4+. There are also some gains in the order: H+ > Ca2+ > Fe3+ > Na+.
Volcanoclastic minerals of some Czechoslovakian tonsteins and their alteration
Authors: Weiss Z. , Baronnet A. , Chmielova M. 
Published: November 2006

AbstractIn the Czechoslovak part of the Upper Silesian Coal Basin (Ostrava-Karvina Coal Basin), only part of the Upper Carboniferous (Namurian A, B, C and Westphalian A) is well developed, and tonsteins, which are clayey rocks or claystones, occur as thin, clayey interlayers in the coal seams. Two types of primary volcanic mineral assemblages were identified in four tonstein samples from different coal seams; the first type is characterized by the presence of biotite and sanidine, and the second by the presence of biotite, bytownite and Ca-amphibole. All tonsteins studied contained kaolinite minerals, volcanic quartz grains, crystals of zircon and apatite. Separated biotite flakes with an admixture of kaolinite layers were identified as 1M polytype. The flakes without kaolinite minerals were identified as epitactic overgrowth of 1M and complex polytypes, and twinned crystals of 2M1 polytype. Kaolinization of biotite flakes was observed in all tonstein samples studied. Kaolinite single layers (7 Å) as well as two-layer polytype of kaolinite minerals (14 Å) sandwiched between biotite layers (10 Å) were identified by HRTEM imaging.
Allophane in weathered zones of barite ore deposits (Vide de Alba and San Blas, Zamora, Spain): mineralogy and genesis
Authors: Perez del Villar L. , Moro M. C. , Cembranos M. L. 
Published: November 2006

AbstractThe allophane studied occurs in the weathered zones of the barite-sulphide-bearing dolomitic levels, interbedded in the barite ore deposits of Vide de Alba and San Bias (Province of Zamora). These ore deposits are interstratified in the Silurian-Devonian sulphide bearing volcano sedimentary materials of the Alcañices Synform. The allophanic samples have been studied by polarizing microscopy, SEM, XRD, DTA, TG, IRS, EMA and chemical analyses, the last after dissolving the samples by acid (HF + HNO3 + 3HCl + H3BO3) and alkaline digestion (0·5 m NaOH). It is suggested that allophane originates from the reaction of acid solutions released during the weathering of sulphides with acid volcanoclastic rocks. Silica-alumina gels were deposited in holes formed during earlier dissolution of the dolomite associated with the barite ores. Later processes of desilication partially transform allophane to gibbsite.
Aluminium activity in soil solution and mineral stability in soils from Galicia (NW Spain)
Authors: Calvo R. , Alvarez E. 
Published: November 2006

AbstractSolutions obtained from soils in the Galicia Region of NW Spain had considerably lower activities of Al3+ when obtained by a speciation procedure (fractionation with an ionic column and application of specific software) than when obtained from concentrations of reactive Al (colorimetry with pyrocatechol violet) by a calculation that only considers simple hydroxylated species. Using the speciation method, many of the solutions obtained from surface horizons are unsaturated for most minerals, especially in granitic areas.
Illite-smectite from the North Sea investigated by scanning tunnelling microscopy
Authors: Lindgreen H. , Garnaes J. , Besenbacher F. , Laegsgaard E. , Stensgaard I. 
Published: November 2006

AbstractTwo samples of illite-smectite (I-S) isolated from Upper Jurassic clays in well 2/7-3 (3365 m) and well 2/11-1 (4548 m) have been investigated by scanning tunnelling microscopy (STM), and the particle shape and dimensions have been correlated to results from transmission electron microscopy (TEM) on shadowed specimens and results from atomic-force microscopy (AFM). By STM, lath-like and equant particles were observed in both samples, some of the particles having sharp edges. In the I-S from well 2/11-1, spiral-shaped particles were also seen. For both samples, the most frequent particle diameter was 100–200 Å. Particle-thickness distributions from STM and TEM were similar for the I-S from well 2/7-3, being dominated by 10 Å thick particles. For I-S from 2/11-1, the STM particle-thickness distribution has a predominance of 20 Å thick particles, but the TEM particle-thickness distribution is broad, with about equal amounts of 20, 30, 40, 50 and 60 Å thick particles. The AFM particle-thickness distribution for this I-S resembles the TEM thickness distribution. It is concluded that mainly thin (10 and 20 Å) particles are seen by STM. Failure of AFM to show sharp particle edges (seen in STM and TEM) might be attributed to the AFM tip movement or tip shape. In STM, I-S particles from well 2/7-3 have peaks along edges, whereas I-S particles from well 2/11-1 have rims. These rims are also seen in AFM and are therefore real geometrical features, probably a result of two-dimensional growth, whereas the spirals in the I-S from well 2/11-1 demonstrate three-dimensional growth. The minimum thickness of most particles is 10 Å.
Electron spin resonance study of donor-acceptor sites in Zr-montmorillonite
Authors: Zanchetta J. V. , Matrod-Bashi A. , Figueras F. 
Published: November 2006

AbstractThe charge transfer process that occurs in two samples of Wyoming montmorillonite of different grain size pillared with Zr by interaction with perylene (Pe) and tetracyanoethylene (TCNE) has been studied. These smectites are strongly affected by the exchange of Zr and appear to be strong electron acceptors and weak donors. The ESR results show that their ability to form charge transfer radicals is related to the details of preparation, which most probably control the accessibility of Pe and TCNE to the internal surface.
Use of bentonite for isolation of radioactive waste products
Authors: Pusch R. 
Published: November 2006

AbstractSodium smectite clay, commercially available in the form of bentonite powder, serves as a very effective water flow barrier and cation exchanger. At bulk densities between 1·9 and 2·2 g/cm3 after water uptake to reach complete saturation, the hydraulic conductivity is of the order of 10−14 to 10−13 m/s. The swelling potential produces a tight contact with confining structures, which makes bentonite ideal as overpack of rock-deposited radioactive canisters and for borehole and shaft sealing. At bulk densities between 1·1 and 1·3 g/cm3, the hydraulic conductivity of smectite gels is still sufficiently low to make them useful as effective grouts for sealing rock fractures. The longevity in a granite environment is very significant and the ultimate transformation residue—hydrous mica (“illite”)—preserves some of the excellent sealing properties of smectites.
Possible confusion between so-called ferrihydrites and hisingerites
Authors: Farmer V. C. 
Published: November 2006

AbstractThe term ferrihydrite, originally defined as a poorly ordered hydrous ferric oxide exhibiting five or more distinctive X-ray diffraction maxima, has come to be extended to include species that exhibit only 4, 3 or 2 of these maxima. It is pointed out here that hisingerites may exhibit a similar 2-line diffraction pattern. The laboratory synthesis of hisingerites show that they can form under soil conditions. Acid oxalate buffer of pH 3, a reagent considered a fairly specific solvent for ferrihydrite, extracts the iron content of these synthetic hisingerites quantitatively.
The effect of dry heating on the chemistry, surface area, and oxalate solubility of synthetic 2-line and 6-line ferrihydrites
Authors: Stanjek H. , Weidler P. G. 
Published: November 2006

AbstractSynthetic 2-line and 6-line ferrihydrites were heated to 400 K, 500 K and 600 K, under dry conditions. Heating to 400 K lowered the ratios of structural OH to Fe2O3 without a phase transformation. The lowest ratios observed at 400 K were 1·23 (2-line) and 0·85 (6-line ferrihydrite) after 1150 h. For 6-line ferrihydrites heated to 400 K, the solubility in oxalate and the BET surface areas decreased with increasing heating time, whereas the unit-cell parameters, the relative peak intensities and the mean coherence lengths did not change significantly. Heating the 2-line ferrihydrites to 400 K produced microporosity.
X-ray photoelectron spectroscopic analysis of halloysites with different composition and particle morphology
Authors: Soma M. , Churchman G. J. , Theng B. K. G. 
Published: November 2006

AbstractThe surface composition of some halloysites with different particle morphology has been investigated by X-ray photoelectron spectroscopy (XPS) before and after removal of external Fe. The Fe(III) 2p3/2 binding energy of external Fe is appreciably smaller than that of structural Fe. Particle morphology is influenced by structural Fe content. The long-tubular halloysite has very little surface Fe, and its concentration tends to increase with the proportion of non-tubular particles in the samples. The spheroidal sample contains the most structural Fe which, however, does not appear to influence particle shape directly. Study by XPS indicates that Fe substitutes for Al in octahedral positions in approximately 1 : 2 proportion. As a result, an increase in octahedral vacancies and cation exchange capacity would be predicted. Further, halloysite layers within a crystal are generally inhomogeneous in composition. Built up like “onion skins”, the surface layers would either be enriched or depleted in Fe depending on the chemical environment in which crystal growth occurs.
Mössbauer spectroscopic and thermogravimetric studies of tin-clay complexes
Authors: Breen C. , Molloy K. C. , Quill K. 
Published: November 2006

AbstractComplexes of SnCl2/montmorillonite have been prepared from solutions which contained 10, 20, 40 and 200 times the cation exchange capacity of the clay, resulting in complexes which contained 1·7, 1·6, 2·8 and 4·6 wt% of tin. Detailed thermogravimetric and variable temperature 119Sn Mössbauer spectroscopic studies of these complexes, both as prepared and following back exchange with Ca2+-ions, have shown that (i) the complexes are quite acidic in nature, and (ii) the majority of the Sn forms an oxy/hydroxy coating over the montmorillonite surface in which the vibrational freedom of Sn depends upon both the Sn content and the state of hydration of the coating.
‘Face-to-Face’ relationships between oxocentred tetrahedra and cation-centred tetrahedral oxyanions in crystal structures of minerals and inorganic compounds
Authors: Krivovichev S. V. , Starova G. L. , Filatov S. K. 
Published: November 2006

AbstractDetailed analysis of the crystal structures of minerals and inorganic compounds containing oxocentred [OCu4] tetrahedra reveals the following principle for relationships between oxocentred tetrahedra and tetrahedral oxyanions (Tn+O4)−(8−n) with T = S6+ or V5+, or triangular pyramidal oxyanions (SeO3)2− (which may be considered as (SeO3E)2− tetrahedra assuming the lone pair E of selenium to be a fourth ligand): (Tn+O4)−(8−n) tetrahedra are ‘attached’ to the oxocentred tetrahedra so that their grounds (O-O-O and Cu-Cu-Cu) are parallel to each other and the mutual orientation is regular (O corners are exactly under Cu corners). We propose to describe these relationships as ‘face-to-face’, meaning that the oxocentred and cation-centred tetrahedra ‘meet’ along their ‘whole’ triangular faces. Geometric characteristics of ‘face-to-face’ relationships are discussed.
Potarite (Pd-Hg) in thermally metamorphosed dunite from the Inazumi-yama
ultramafic complex, southwestern Japan: an implication for the behaviour of
mercury in PGE mineralization in peridotite
Authors: Arai S. , Prichard H. M. , Matsumoto I. , Fisher P. C. 
Published: November 2006

Abstract
Pd-rich PGM (platinum-group minerals) have been found in sulphide-bearing
dunites and harzburgites from the Inazumi-yama ultramafic complex in southwestern
Japan. In the dunite, potarite (PdHg0.85–0.88) is the most
abundant PGM but other associated PGM include stibiopalladinite
(Pd5Sb2) and rare sperrylite
(PtAs2) and Pd-rich alloys. A Pd telluride has been found
in the harzburgite. The PGM are enclosed usually by pentlandite-heazlewoodite
composite grains and, rarely, by altered chrome-spinel. These minerals are
characteristic of an ultramafic assemblage but they are accompanied by ubiquitous
galena and minor sphalerite not usually associated with these ultramafic
assemblages. The ultramafic part of this complex has been thermally metamorphosed
(olivine-talc zone) within the contact aureole of an adjacent granite. The PGM,
sulphides and altered spinel are all intergrown with antigorite and/or chlorite,
indicating a metamorphic overprint on the primary igneous mineralogy. The Pd/Pt
ratios of 9 suggest a process of hydrothermal concentration for the Pd and it is
proposed that the Pd has been remobilized and reconcentrated by hydrothermal
solutions derived from the granitic magma which reacted with the Pd concentrated
in the primary magmatic sulphides. Mercury may have been leached from surrounding
sediments by the hydrothermal solutions. It is possible that potarite and the
other PGM formed at temperatures of up to 650°C and are likely to be found in
other thermally metamorphosed ultramafic rocks showing a depleted character
(spinel Cr/[Cr+Al]>0.7), common in orogenic belts.
The phase system Fe-Ir-S at 1100, 1000 and 800°C
Authors: Makovicky E. , Karup-Møller S. 
Published: November 2006

Abstract
Phase relations in the dry condensed Fe-Ir-S system were determined at 1100,
1000 and 800°C. Orientational runs were performed at 500°C. Between 1100 and
800°C, the system comprises five sulphides and an uninterrupted field of γ(Fe,Ir).
Fe1-xS dissolves 5.8 at.% Ir
at 1100°C, 3.4 at.% Ir at 1000°C and 1.0 at.% Ir at 800°C. The solubility of Fe in
Ir2S3, IrS2 and
IrS~3 increases with decreasing temperature, reaching 2.5
at.% in the latter two sulphides at 800°C. Thiospinel
‘FeIr2S4— is non-stoichiometric, from
Fe22.3Ir19.8S58.0
to
Fe18.9Ir23.1S58.0,
depending on aS and
aFe, i.e. on a phase
association. Thiospinel is absent at 800 and 500°C.
Scapolite pegmatite from the Minas fault, Nova Scotia: tangible manifestation
of Carboniferous, evaporite-derived hydrothermal fluids in the western Cobequid
highlands?
Authors: Owen J. V. , Greenough J. D. 
Published: November 2006

Abstract
Pegmatite cutting chlorite schist in the Minas fault at McKay Head, Nova
Scotia, consists of Cl-rich (2.7–3.8 wt.% Cl) marialitic scapolite
(EqAn21–32) with interstitial, apparently primary
analcite, hematite and rutile, and later (including vug-lining) analcite, pyrite,
chlorite, titanite and calcite, and cross-cutting epidote veins. Some of the
latter phases might have crystallized from residual pegmatitic fluids. Unlike many
other primary scapolite-bearing igneous rocks, the McKay Head occurrence has
compositional affinities with mafic (rather than felsic) systems: it is enriched
in transition metals (e.g. Cr≤53 ppm), and has very low LILE concentrations (e.g.
Rb<10 ppm; U<1 ppm; Th<2 ppm; Ba<20 ppm) and Rb/Sr ratios (~0.05). The
presence of interstitial rutile and hematite rather than ilmenite indicates that
the pegmatitic fluid was oxygenated late (T~400°C) in
its crystallization history.
The pegmatite is interpreted to be related to highly sodic hydrothermal
solutions derived from (or affected by) early Carboniferous evaporites of the
Windsor or Horton groups. Compositionally-similar fluids, perhaps also related to
an evaporite source, may be responsible for a regional, early Carboniferous
Na-metasomatic event that altered a suite of alkaline granitoid intrusions shortly
after their emplacement.
Extreme closed system fractionation of volatile-rich, ultrabasic peralkaline
melt inclusions and the occurrence of djerfisherite in the Kugda alkaline complex,
Siberia
Authors: Henderson C. M. B. , Kogarko L. N. , Plant D. A. 
Published: November 2006

Abstract
Djerfisherite
[K6(Cu,Fe,Ni)25S26Cl]
has been found as a daughter mineral in melt inclusions in melilite from a Kugda
melilitolite. The inclusion mineral assemblage includes pyrrhotite, pentlandite,
forsterite, diopside, monticellite, phlogopite, wollastonite, nepheline, sodalite,
combeite, calcite, Na-K-Ca carbonate, and hydrated calcium silicates. The
djerfisherite is Ni-rich rather than Cu-rich consistent with an ultimate upper
mantle magma source. The djerfisherite-bearing assemblage formed from primary
carbonate/alkali-rich, melilititic melt inclusions which underwent extreme,
closed-system, magmatic to postmagmatic fractionation over a temperature range of
>1000° to <500 °C.
Significance of allanite-(Ce) in granitic gneisses from the ultrahigh-pressure
metamorphic terrane, Dabie Shan, central China
Authors: Liu Xiaochun , Dong Shuwen , Xue Huaimin , Zhou Jianxiong 
Published: November 2006

Abstract
A recent study of granitic gneisses in the ultrahigh-pressure (UHP)
metamorphic terrane from Dabie Shan, central China reveals that allanite-(Ce) is a
widespread REE-bearing accessory phase. The microprobe
analyses show that allanites-(Ce) have nearly uniform chemical compositions, with
total REE contents ranging from 23 to 28 wt.% and a
La/Ce ratio of 0.57–0.73. All allanites-(Ce) are replaced or rimmed by epidotes
and commonly form a relatively REE-poor rim near the
interfaces. The textural relations and mineral chemistry suggest that
allanite-(Ce) crystallized prior to metamorphism and therefore was of igneous
origin, whereas the surrounding epidote was the product of metamorphism. Granitic
gneiss, composed chiefly of sodic plagioclase, microcline and quartz with minor
amounts of Mn-rich garnet, biotite, low Si phengitic mica, epidote, chlorite and
sometimes amphibole, was formed at 495°C and ∼5 kbar, corresponding to the
retrograde metamorphism of UHP rocks. Accordingly, it is believed that granitic
gneisses have not experienced UHP metamorphism. This implies that a large scale
tectonic juxtaposition developed before the epidote-amphibolite facies retrograde
metamorphism of UHP rocks during the late continental collision in Dabie
Shan.