bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characteristics of clays in an Oxisol-Spodosol toposequence in Amazonia (Brazil)
Authors: Bravard S. , Righi D. 
Published: November 2006

AbstractThe clay fraction of soils from a toposequence developed on a sandy clay Tertiary sediment in the Brazilian Amazonia was studied. Clayey Acrorthox located at the upper part of the sequence have transformed progressively into sandy Tropohumods down the slope. Along the slope important chemical and mineralogical changes linked to modifications in the weathering conditions were observed. In the Acrorthox the hydrolysis process largely prevails and the clay fraction is composed mainly of Fe-rich kaolinite. Fe and Al amorphous compounds become increasingly abundant along the slope. In the Spodosols, hydrolysis and acidocomplexolysis processes have both been effective, and the clay fractions contain not only more gibbsite, but also amorphous materials which are particularly abundant in the Bh horizons.
The nature of an iron oxide—organic iron association in a peaty environment
Authors: Schwertmann U. , Murad E. 
Published: November 2006

AbstractFe oxides deposited in ditches draining a bog in the Harz Mountains, Northern Germany, consist essentially of a two-XRD line ferrihydrite that has a magnetic hyperfine field of only 46·5 T at 4·2 K. Pyrophosphate extraction led to an incomplete separation of this from organically-bound Fe, which was depleted in the residue and particularly enriched in the dialysate of the extract. Decomposition of humics with H2O2 led to a further depletion of organic Fe, but also increased the number of XRD lines of the ferrihydrite to six, and raised the hyperfine field by ∼1 T. These modifications are probably the result of an improved interparticle coherence.
Study of a chlorite-smectite interstratified mineral by means of the Inter program
Authors: Ruiz-Amil A. , Vila E. , Aragón de la Cruz F. 
Published: November 2006

AbstractA chlorite-smectite interstratified mineral in a pottery stone from Niwatorizawa mine, Izushi-Cho, Hyogo Prefecture (Japan), has been studied by means of Fourier transform methods, together with interlamellar sorption of ethylene glycol and glycerol. The calculations were carried out with the INTER program (using an Olivetti M-24 personal computer with MS-DOS operating system) which allows the analysis of two-component interstratified structures by two Fourier transform based methods: the X-ray diffraction intensity function method, and the interlayer distances distribution function method. The material studied contains a 1:1 chlorite-smectite interstratification and shows a marked tendency to alternation, i.e., the interstratification is almost regular.
Decomposition of alkylammonium cations intercalated in vermiculite
Authors: Pérez-Rodríguez J. L. , Morillo E. , Maqueda C. 
Published: November 2006

AbstractDecomposition of decylammonium cations on vermiculite surfaces as a result of acidity has been studied. The vermiculite-decylammonium complex was treated with solutions of HCl in water and butanol, and solutions of chlordimeform in butanol. X-ray powder diffraction and IR spectroscopy data showed the presence after treatment of ammonium cations in addition to aliphatic chain compounds in the interlamellar space. The ammonium cation is produced by breaking of the C-N bond of alkylammonium due to the low pH of the medium and, when using butànol as solvent, to the dissociation of the scarce water molecules on the clay surface. The influence of the different solutions on the period of decomposition of alkylammonium cations is discussed. Vermiculite-decylammonium complex treated with HCl solutions for a year released structural Mg2+ due to the acidity of the medium. This Mg2+ partially displaced ammonium cations from the interlamellar space.
Structural alteration of sepiolite by dry grinding
Authors: Cornejo J. , Hermosin M. C. 
Published: November 2006

AbstractThe effects of dry grinding on the structure of sepiolite were studied by XRD, surface area measurement, TG-DTA and IR spectroscopy techniques. The results show that the sepiolite framework is rather resistant to mechanical stress and its alteration by dry grinding occurs through three successive, overlapping processes: (i) thinning of the fibrous particles without structural alteration; (ii) distortion of the parallel units of sepiolite fibres, affecting essentially the particle surface which transforms into an amorphous protective coating; (iii) disruption of the inner structure and a prototropy effect, producing an amorphous phase with some residual order.
Chemical and mineralogical characterization of a Cretaceous clay from the Lousã Basin (Central Portugal)
Authors: Prudêncio M. I. , Waerenborgh J. C. , Cabral J. M. P. 
Published: November 2006

AbstractSamples of two lenticular clay bodies from a Cretaceous deposit near Padrão (Lousã basin) were characterized by INAA, XRD and Mössbauer spectroscopy. This clay is believed to be the raw material used to manufacture the Iron Age and Roman fine grey pottery from Conímbriga. The differences observed in the chemical and mineralogical compositions of the clay samples and of different size fractions are consistent with the high variance found in the compositional group corresponding to that archaeological site.
Halloysite Formation ThroughIn SituWeathering of Volcanic Glass from Trachytic Pumices, Vico's Volcano, Italy
Authors: Quantin P. , Gautheyrou J. , Lorenzoni P. 
Published: November 2006

AbstractThe weathering of a trachytic pumice within a pyroclastic flow underlying an andic-brown soil on the volcano Vico has been studied. The main mineral formed is a spherical 10 Å halloysite which has been shown by SEM andin situmicroprobe analysis to have formed directly from the glass. The major mineralogical characteristics as determined by XRD, IR, DTA, TEM and microdiffraction are typical of 10 Å halloysite. However, some minor mineralogical properties and the high Fe and K contents, suggest that it is an interstratification of 74% halloysite and 26% illite-smectite. The calculated formula of the hypothetical 2:1 minerals reveals an Fe- and K-rich clay, with high tetrahedral substitution, like an Fe-rich vermiculite, but the detailed structure of this mineral remains uncertain.
Layer-silicates in the contact zone between granite and serpentinite, jordanów, lower Silesia, Poland
Authors: Dubińska E. , Wiewióra A. 
Published: November 2006

AbstractChlorite belonging to subfamily C, vermiculite 2MB-VII-meso, talc and a monoclinic amphibole were identified in rocks from a contact zone between highly tectonized granite and serpentinite at Jordanów, Lower Silesia, Poland. K-saturated vermiculite readily produced a phlogopite-like structure 1M-I (3TA-IV) indicating trioctahedral mica to be its precursor. Spatial relations of the mineral assemblages were compared with published experimental data and used to produce a tentative model of the geological evolution of the rocks and minerals, which include four episodes of mineral development separated by three tectonic events.
Cation site occupancy in chlorites and illites as a function of temperature
Authors: Cathelineau M. 
Published: November 2006

AbstractThe relationships between the composition and the crystallization temperature of chlorites and illites have been investigated in different geothermal fields and in particular the Los Azufres system in Mexico, considered to be a natural analogue to experimental laboratories, as the main changes in physical and chemical conditions and mineralogy are related to progressively increasing temperature with depth. Temperature was estimated from combined geothermometric approaches, and especially from fluid inclusion studies on quartz coexisting with clays. The Al(IV) content in the tetrahedral site of chlorites, and the K content and total interlayer occupancy of illites increase with temperature. These chemical changes are mainly related to the marked decrease in the molar fraction of the Si(IV)-rich end-members (kaolinite for chlorites, and pyrophyllite for illites) which become negligible at ∼300°C. Other chemical changes, such as the variation in Fe and Mg contents, are partly influenced by temperature, but are strongly dependent on the geological environment, and consequently on the solution composition. The empirical relationships between chemical variables and temperature were calibrated from 150–300°C, but extrapolations at lower and higher temperatures seem possible for chlorites. Such geothermometers provide tools for estimating the crystallization temperature of the clays, and are important for the study of diagenetic, hydrothermal and low-T metamorphic processes.
Clay minerals as records of temperature conditions and duration of thermal anomalies in the Paris Basin, France
Authors: Clauer N. , O'neil J. R. , Furlan s. 
Published: November 2006

AbstractUpper Triassic sandy horizons in the Paris Basin were sampled at depths ranging from outcrop in the northeast to 2,700 m in the centre of the basin. The smallest clay sub-fractions (<0.2 μm) from the deepest central samples consist mainly of illite and chlorite whose K-Ar age is ∼ 190 Ma. These minerals formed at a relatively high temperature of 220-250°C, as determined from the oxygen isotope fractionation between authigenic illite and associated quartz overgrowths, but at a burial depth of only 500 m. In a nearby drillhole that crosscuts a fault zone reactivated during the 190 Ma event, illite is less well-crystallized and has a higher δ18O value suggesting different physical and chemical conditions of formation during the same hydrothermal episode. Two other generations of illite-smectite mixed-layer clays formed in the same Triassic horizon: one at ∼150 Ma and the other at ∼80 Ma. These younger clays have higher δ18O values and thus may have formed at somewhat lower temperatures. The δ18O values of the fluids from which the different illite-smectite mixed-layer minerals form range from +9 to +13.5 per mil (SMOW).An Ar diffusion code was used to estimate, on the basis of the Ar loss of the clay-type material, the duration of these events. The results suggest that the duration of the hydrothermal events at 190 Ma and 150 Ma were rather short, <1 Ma, whereas the youngest event was protracted over a much longer period of ∼37 Ma. Comparison between K-Ar ages of the different mixed-layer minerals and sedimentation rates of the sediments since the Palaeozoic shows significant accelerations of the rates at ∼ 190-200 Ma and 150 Ma, and a less important one at ∼80 Ma. These observations provide additional evidence that the first two events were promoted by basement-related tectono-thermal activities. The third event is considered to be of diagenetic origin.
Tschermak substitution as an indicator of palaeotemperature in Silurian K-bentonites from the Southern Uplands of Scotland and Northern Ireland
Authors: Pearce R. B. , Clayton T. 
Published: November 2006

AbstractChemical analyses of the <0.2 μm illite-smectite (I-S) fraction from K-bentonites in Silurian age sediments sampled from three different localities in the Southern Uplands of Scotland and Northern Ireland indicate that the I-S from the three localities shows differences in both K+ content and the degree of Tschermak substitution of octahedral Al3+ for Mg2+. The K+ content correlates with percentage expandability (%E) of I-S as determined by X-ray diffraction (XRD), but both these parameters show poor correlation with palaeotemperature as estimated by organic reflectance methods. Octahedral Mg2+ content shows an inverse correlation with Al3+, and both these parameters show a good correlation with estimated palaeotemperature. Although K-substitution has been retarded at Dob's Linn, the region subjected to the highest temperature, Tschermak substitution of Al3+ for Mg2+ has apparently continued. In these K-bentonites, Tschermak substitution appears to be a better indicator of palaeotemperature than K-substitution.
Thermogravimetry/evolved water analysis (TG/EWA) combined with XRD for improved quantitative whole-rock analysis of clay minerals in sandstones
Authors: Thornley D. M. , Primmer T. J. 
Published: November 2006

AbstractCurrent methods of quantitative whole-rock clay mineral analysis of sandstones often provide little more than an estimate of clay mineral abundances, especially where the total clay mineral content is <10 wt% of the sandstone. More accurate determinations of clay mineral abundance in the whole rock can be made by combining thermogravimetry/evolved water analysis (TG/EWA) and X-ray diffraction (XRD) data. The TGA/EWA system incorporates a purpose built thermobalance linked to a water specific infrared detector which is used to measure quantitatively the clay mineral dehydroxylation water evolved from the whole rock when heated from 250°C to 900°C. This gives a measure of the total hydroxyl content of the clay minerals in the whole rock which, when combined with XRD analysis of a separated clay size-fraction, enables individual clay mineral abundances in the whole-rock sample to be determined. Results on artificial sand/clay mineral mixtures prepared with known amounts of different clay minerals (chlorite, illite and kaolinite) show that the accuracy of the combined method is most influenced by the accuracy of the XRD data. Errors associated with TG/EWA were found to be negligible by comparison. A case study is included in which the technique has been used to determine accurately the illite abundance in the Magnus Sandstone Reservoir, Northern North Sea.
The natural occurrence of x-alumina in lateritic pisolites
Authors: Singh Balbir , Gilkes R. J. 
Published: November 2006

AbstractPisolites in the bauxitic laterites of Darling Range, Western Australia may contain up to 50% AI2O3, although no major Al-containing phases can be identified using standard X-ray diffraction techniques. These pisolites have been investigated using a range of techniques, and it has been demonstrated that Al is present in the form of x-alumina, a poorly crystalline form of A12O3. The x-alumina exhibits an indurating morphology and appears to have formed from a hydrated precursor.
Mafic phyllosilicates in low-grade metabasites. Characterization using deconvolution analysis — discussion
Authors: Hillier S. 
Published: November 2006

AbstractAny X-ray diffraction (XRD) pattern of mixed-layered maximum R1 ordered chlorite-smectite has an exact equivalent R0 smectite-corrensite or R0 chlorite-corrensite. The identification of a mineral as chlorite (0.8)-smectite R1 is, therefore, not evidence that the fundamental layers in such an interstratified structure are actually chlorite and smectite. Furthermore, there are no obvious differences between XRD patterns of R0 and R1 chlorite-smectite at high or low smectite contents. Therefore the frequently supposed identification of R0 chlorite-smectite with high smectite contents is also questionable. It follows that the identification of R1 chlorite (0.8)-smectite by Robinson & Bevins (1994) and of R0 chlorite (≈0.2)-smectite in an earlier publication (Robinson et al.,1993) cannot be used as evidence regarding the debate over the nature of the component layers in interstratified minerals intermediate between trioctahedral smectite and chlorite.Diffraction patterns of natural mixed-layer chlorite minerals from metabasites often show a strong reflection at 31 Å yet a lack of resolution of other mixed-layer peaks from those of discrete chlorite. These features cannot be matched by any single mixed-layer mineral consisting of layers of chlorite and smectite and were matched by Robinson & Bevins (1994) using a mixture of different chlorite-smectite minerals. However, they can be matched by a single chlorite-corrensite mineral in which there is an element of segregation of layer types. These different possibilities need to be investigated further.
The flow characteristics of halloysite suspensions
Authors: Theng B. K. G. , Wells N. 
Published: November 2006

AbstractThe rheology of aqueous suspensions of Na halloysites with different particle shape has been investigated using a Haake rotary viscometer. Three halloysites from New Zealand were used: Matauri Bay (MB), Te Akatea (TA) and Opotiki (Op) which are mainly composed of thick long tubules, short thin laths, and spherules, respectively. Suspensions of the materials subsequently prepared from the MB and TA samples show a pseudoplastic consistency under shear, characterized by a steep initial rise in shear stress as shear rate increases, followed by a linear increase in stress when a certain shear rate is exceeded. The Op halloysite, on the other hand, shows Newtonian flow behaviour for which shear stress increases linearly with shear rate throughout. For MB and TA, the shear stress developed during rotor acceleration is larger than that produced during deceleration, and the corresponding flow curves enclose a hysteresis loop. As suspension pH increases, the pseudoplastic character decreases as does the amount of hysteresis. Above pH 7.5, flow approaches Newtonian and hysteresis is absent. Plots of Bingham yield value against pH at different ionic strengths (0.003, 0.03 and 0.3 M NaCl) intersect at pH 6.0 for MB and at pH 7.1 for TA. These values are identified with the point of zero charge (PZC) of the particle edge surface. The flow characteristics of halloysites may be explained in terms of the influence of particle shape, pH, electrolyte concentrations, and layer composition on particle interactions.
Reconstruction of palaeothermal conditions in a passive margin using illite-smectite mixed-layer series (BA1 scientific deep drill-hole, Ardeche, France)
Authors: Renac C. , Meunier A. 
Published: November 2006

AbstractThe comparison between measured and predicted smectite percent (%Sm) in an illite-smectite (I-S) mixed-layer series was used to estimate the thermal conditions of diagenesis in the Ardèche sedimentary series. Measurements were performed using the decomposition procedure (Lanson & Besson, 1992) of XRD patterns obtained from oriented preparations (<0.2 μm fractions). Three particle populations were identified: I-S, poorly crystallized illite (PCI), and well crystallized illite (WCI); the %Sm was measured in the I-S population by comparison with calculated XRD patterns using the NEWMOD software (Reynolds, 1985). The theoretical evolution of %Sm with depth obtained with the two first-order kinetic reaction processes described by Velde & Vasseur (1992) was compared to the measured one at Balazuc. The best fit was obtained for the following conditions: 35°C km–1and between 1500 and 2000 m for the thermal gradient and the eroded piles, respectively. The predicted values for I-S compositions in the 10–0% Sm range are overestimated by the model because the reaction controlling the composition is no longer the dissolution of I-S but the ripening of illitic particles (PCI and WCI).Two zones can be distinguished in the sedimentary series: (1) down to 55 m, the %Sm of I-S particles is highly variable and seems to be controlled by local variations in permeability and chemical composition; (2) down to 550 m, the %Sm of I-S particles is more strictly dependent on the general time-temperature conditions. An anomalously high %Sm value is located in the vicinity of faults at 1669 m due to local change of the water/rock ratio.
Distribution of Fe in the fine fractions of some Czech bentonites
Authors: Lego S. , Morháčová E. , Komadel P. 
Published: November 2006

AbstractDistribution of Fe in the fine fractions of four Czech bentonites was investigated by M6ssbauer spectroscopy. The spectra at room and liquid nitrogen temperatures revealed that most Fe present in the samples is structurally bound in smectite. Microcrystalline and/or Al-substituted goethite was identified in all fine fractions, comprising 8 to 50% of total Fe. This mineral was partly magnetically ordered in the Rokle sample even at room temperature. Two per cent of total Fe was bound in hematite in the Krásný Dvoreček sample. Only octahedral Fe(III) was found in the Rokle and Stebno samples, while Krásný Dvoreček and Hroznětín contained 9 and 38%, respectively, of the total Fe as octahedral Fe(II) and 14% of total Fe was found as tetrahedral Fe(III) in Krásný Dvoreček.
Stable isotopic signatures of authigenic minerals in a Holocene ophiolitic debris flow, Southland, New Zealand
Authors: Craw D. , Blattner P. , Landis C. A. 
Published: November 2006

AbstractAuthigenic chrysotile, stevensite, calcite, aragonite and pectolite have formed together in a Holocene ophiolitic debris flow in Southland, New Zealand. Mineral growth occurred about 4700-5700 years ago. The temperature of formation of these minerals is estimated from climatological data to be 5–10°C Surface water and groundwater δ180 is currently about –10‰, and was estimated to be about –9.5±1‰ during mineralization. Coexisting calcite (δ180 = +23‰) and aragonite (δl8O = +24‰) were in equilibrium with each other and with the groundwater at 5–10°C Stevensite δ180 is +14 to +16‰, chrysotile has δ180 = +5.5‰, and authigenic pectolite has δ180 near +10‰. Carbon isotope ratios for calcite and aragonite are strongly depleted (δ13C = –13 to –18) which suggests that dissolved CO2 had δ13C below -27. This isotopically light carbon probably resulted from a high organic component of carbon dissolved in the groundwater.
Electron microscopy study of n-butylammonium vermiculite swelling
Authors: McCarney J. , Smalley M. V. 
Published: November 2006

AbstractElectron microscopy was used to study swollen samples of n-butylammonium vermiculite prepared in dilute aqueous solutions of n-butylammonium chloride. Three electrolyte concentrations were studied, 0.1 M, 0.01 M and 0.001 M. The 0.1 M samples studied were in a taetoid phase, exhibiting crystalline legions of about ten layers separated by large irregular aqueous regions. The dilute samples were studied in their gel phase, exhibiting regular spacings of 85 nm and 55 nm in the 0.001 M and 0.01 M solutions, respectively. These spacings are much larger than those measured previously by neutron scattering, probably due to an additional expansion of the interlayers during the freezing process employed in preparing the replicas. In all examples, the structures were found to be lamellar over regions of several microns.
Interaction of Fe-oxyhydroxide colloidal particles with montmorillonite
Authors: Ferreiro E. A. , Helmy A. K. , De Bussetti S. G. 
Published: November 2006

AbstractInteraction between positively charged Fe-oxyhydroxide (β-FeOOH) particles and negatively charged particles of montmorillonite was studied as a function of particle concentration, pH and time. The results showed that the clay particles appear to bridge between FeOOH particles leading to associations in which the ratio of positive to negative particles varied between 1.4 and 2.56 depending on pH and particle concentrations. The data could be represented by isotherms of interaction of the high affinity type and, together with the interaction kinetics, could be described by Langmuir type formulations.