bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chlorite Geothermometry?—Contamination and Apparent Octahedral Vacancies
Authors: Jiang Wei-Teh , Peacor Donald R. , Buseck Peter R. 
Published: August 2006

AbstractThe large contents of octahedral vacancies in published formulae of chlorite from hydrothermal systems and clastic sequences are shown to be largely caused by inclusion of other minerals. Verification is provided by analytical electron microscope (AEM) analyses of chlorite in pelitic rocks from the Gaspé Peninsula, Quebec and the Gulf Coast, Texas. The Gaspé chlorite occurs as discrete crystals locally coexisting with corrensite, and the Gulf Coast chlorite is free of mixed layers other than local serpentine-like 7-Å layers. Unlike most electron microprobe analyses (EMPA), but like other AEM analyses, the reported chlorite formulae do not have significant octahedral vacancies, are not Si-rich and (Fe + Mg)-poor relative to classic metamorphic chlorite, and have nearly equal amounts of tetrahedral and octahedral Al. The studied chlorites and those in metabasites and clastic rocks that could be positively identified as containing no or minimal mixed layering or submicroscopic intergrowths have little or no Ca or alkalis. In contrast, EMPA of chlorite reported for other clastic sequences show variable amounts of Na + K + 2Ca that exhibit a poorly defined positive correlation with the proportion of octahedral vacancies. The EMPA of chlorite from the Salton Sea and Los Azufres geothermal fields that were suggested to contain temperature-dependent amounts of tetrahedral Al (and thus used as “chlorite geothermometers”) show compositional characteristics similar to those reported for several saponite-chlorite transition series in metabasites.Continuous increases in octahedral occupancy and tetrahedral Al with increasing metamorphic grade are attributed to decreases in abundance of mixed layers or fine-grained intergrown minerals that commonly occur as a result of increasing crystal size and homogeneity in prograde sequences. Use of “chlorite geothermometry” based on the proportion of apparent octahedral vacancies or tetrahedral Al is therefore unwarranted and leads to inaccurate temperature estimates.
Effect of the Presence of Aluminum Ions in Iron Solutions on the Formation of Iron Oxyhydroxides (FeOOH) at Room Temperature Under Acidic Environment
Authors: Singh S. Shah , Kodama Hideomi 
Published: August 2006

AbstractThe hydrolytic behavior of Fe solutions at room temperature under acidic conditions was investigated. In the presence of Al ions, with Cl and NO3 as associated anions, the Fe hydrolysis began almost instantaneously and a crystalline β-FeOOH (akaganeite) was formed in the AlCl3/FeCl3 system within a short period. Initially the particles were small with large surface area. However, with time the particles grew in size and the surface area decreased. After about 42 days of equilibration, the akaganeite particles grew to 60–300 nm long, 10–50 nm wide and with a surface area of 55 m2/g, which is similar to other reports for akaganeite prepared at higher temperatures. In the NO3 system [Al(NO3)3/Fe(NO3)3], lepidocrocite (γ-FeOOH) and goethite (α-FeOOH) were formed. In a mixed anion system (Cl/NO3) solid phases identified were akaganeite (β-FeOOH) and lepidocrocite (γ,-FeOOH). The introduction of poly-nuclear hydroxy-Al along with monomer Al in Cl and NO3 systems of Fe affected the quantity and quality of the solid phase. The crystallinity of β-FeOOH formed in the presence of polynuclear hydroxy-Al ions in a Cl-system was more disordered than when it formed in the presence of monomer Al-ions alone. In NO3 systems, polynuclear hydroxy-Al hindered the formation of goethite (α-FeOOH). Our experiments showed that Fe oxyhydroxides crystallize readily under acidic conditions in the presence of Al ions and the data also indicated that the Cl was essential for the crystallization of akaganeite, whereas goethite was formed in those systems when Cl was absent.
The Sol Concentration Effect in n-Butylammonium Vermiculite Swelling
Authors: Williams G. D. , Moody K. R. , Smalley M. V. , King S. M. 
Published: August 2006

AbstractThe swelling of n-butylammonium vermiculite in water was investigated as a function of the sol concentration (r), the salt concentration (c) and the temperature (T).The interlayer spacing in the gel phase was investigated as a function of r and c by neutron diffraction and by laboratory experiments which measured how many times its own volume a crystal would absorb. The salt concentration was found to be the stronger variable with the interlayer spacing decreasing proportional to c0.5, which is consistent with previous results and with the Coulombic attraction theory. The sol concentration was found to affect the swelling for two reasons, the salt fractionation effect and the trapped salt effect. Both of these cause the salt concentration in the supernatant fluid to be greater than that originally added to the crystals and so reduce the swelling.A new method was used for extracting the solution from inside the gels by collapsing the gels by the addition of potassium hydrogen carbonate. The Volhardt titration was carried out on the extracted and supernatant solutions from about 250 gels. The ratio of the external to the internal chloride concentration was found to be approximately constant across the range of salt concentrations. Its average value was equal to 2.6, again in agreement with Coulombic attraction theory and showing the surface potential to be constant at about 70 mV.The (r, c, T) boundary of the two phase colloid region was investigated by three methods. A plot of log c against Tc was linear within experimental accuracy, with a gradient of 0.077 K−1 or 13 K per log unit. This shows that the surface potential varies by only 1 mV per decade in the salt concentration. The system is therefore governed by the Dirichlet boundary condition and not by the Nernst equation.
The Center Shift in Mössbauer Spectra of Maghemite and Aluminum Maghemites
Authors: Da Costa G. M. , De Grave E. , Bowen L. H. , Vandenberghe R. E. , De Bakker P. M. A. 
Published: August 2006

AbstractSynthetic, relatively well-crystallized aluminum-substituted maghemite samples, γ-(Aly·Fe1−y)2O3, with y = 0, 0.032, 0.058, 0.084, 0.106 and 0.151 have been studied by X-ray diffraction and zero-field Mössbauer spectroscopy in the range 8 K to 475 K, and also with an external field of 60 kOe at 4.2 K and 275 K. It was found that there are two different converging models for fitting the zero-field spectra of the maghemites with a superposition of two Lorentzian-shaped sextets, both resulting in inconsistent values for the hyperfine fields (Hhf) and/or the center shifts (δ) of the tetrahedral (A) and octahedral (B) ferric ions. From the applied-field measurements it is concluded that there is a constant difference of 0.12 ± 0.01 mm/s between δB and δA, regardless of the Al content. For the Al-free sample the center shifts are found as: δA = 0.370 mm/s and δB = 0.491 mm/s at 4.2 K and δA = 0.233 mm/s and δB = 0.357 mm/s at 275 K (relative to metallic iron), with an estimated error of 0.005 mm/s. Both δA and δB are observed to decrease with increasing Al concentration. The effective hyperfine fields for the non-substituted maghemite sample are: Heff,A = 575 kOe and Heff,B = 471 kOe at 4.2 K and Heff,A = 562 kOe and Heff,B = 449 kOe at 275 K, with an error of 1 kOe. The B-site hyperfine field remains approximately constant with Al substitution, while for the A site a slight decrease with increasing Al content was observed.
Kaolinite/Montmorillonite Resembles Beidellite
Authors: Cuadros J. , Delgado A. , Cardenete A. , Reyes E. , Linares J. 
Published: August 2006

AbstractA number of smectitic samples from Almeria (SE Spain) were studied by chemical analysis, DTA, TG, XRD (oriented aggregates with ethylene glycol treatment and Greene-Kelly test), FTIR and MAS NMR. Chemically they resembled a beidellite-montmorillonite series, displaying DTA/TG characteristics already quoted in the literature in beidellite descriptions. They did not swell after the Greene-Kelly test, as it has also been reported for some beidellites. Nevertheless XRD of the oriented, glycolated samples, FTIR, MAS NMR and revision of the chemical analysis demonstrated that they were mixed-layered kaolinite/montmorillonite. It is possible that some of the reported beidellites in the literature are kaolinite/montmorillonite. Beidellite characterization must be supported by several different techniques.
Nature and Stability of Radiation-Induced Defects in Natural Kaolinites: New Results and a Reappraisal of Published Works
Authors: Clozel Blandine , Allard Thierry , Muller Jean-Pierre 
Published: August 2006

AbstractA new appraisal of radiation-induced defects (RID) in natural kaolinite, i.e., positive trapped holes on oxygen atoms, has been undertaken using Q-band EPR spectra, recorded at 93 K, of irradiated annealed and oriented kaolinite samples originating from various environments. Three different centers were identified. Two of the centers, A- and A’-centers, are trapped holes on oxygen from Si-O bonds. They have a distinct signature and orthogonal orientation, i.e., perpendicular and parallel to the (ab) plane, respectively. The third center, the B-center, is a hole trapped on the oxygen bonding Al in adjacent octahedral positions (AlVI-O−-AlVI bridge). This confirmed some previous assignments from the literature, some others are no longer considered as valid.A least squares fitting procedure is proposed to assess the RID concentration in any kaolinite. It allows a quantitative approach of the thermal stability of RID. Isochronal annealing shows that the thermal stability of the centers decreases in the order A, A′, B over the temperature range 0–450°C: (1) B-center is completely annealed above 300°C; (2) A′-center can be annealed by heating at 400°C for more than two hours; (3) A-center is stable up to 450°C. The activation energy and the magnitude of the mean half-life for A-center is evaluated through isothermal annealing at 350, 375 and 400°C, with Ea = 2.0 eV ± 0.2, and t½ > 1012 years at 300 K. The stability of A-center seems to decrease with increasing crystalline disorder. Nevertheless, it is high enough for radiation dosimetry using kaolinites from any environment on the Earth's surface.
Development of Microporosity in Clinochlore Upon Heating
Authors: Villieras F. , Yvon J. , Cases J. M. , de Donato P. , Lhote F. , Baeza R. 
Published: August 2006

AbstractThe “modified chlorite structure” forms by the dehydroxylation of the interlayer octahedral sheet of magnesian chlorite at around 500°C and results in a structure with a basal spacing near 27 Â (Brindley and Chang 1974). This process involves drastic textural modifications as indicated by gas adsorption experiments which reveal the formation of structural micropores. Infrared spectroscopy as well as thermogravimetry and mass spectrometric analysis show that these micropores are filled with molecular atmospheric water, carbon dioxide, nitrogen, argon and hydrocarbons which condense once the samples cool down. A high temperature treatment is needed in order to release the different phases. A heterogeneous dehydroxylation mechanism is proposed in which micropores are formed in donor regions and magnesium and oxygen are concentrated in acceptor regions. This leads to a 27 Å structure with micropore zones and enriched interlayer oxide zones alternating along the z-axis of the mineral.
Biogenic Nontronite from Marine White Smoker Chimneys
Authors: Köhler Birgit , Singer Arieh , Stoffers Peter 
Published: August 2006

AbstractClay samples of greenish colour were collected from submarine hydrothermal chimneys of the Galapagos Rift and Mariana Trough. Mineralogical and chemical investigations of the clay by scanning and transmission electron microscopy, X-ray diffraction, differential thermal analysis, infrared-spectros-copy, X-ray fluorescence, and determination of specific surface area, and oxygen isotope composition identify it as a well crystallized nontronite. This nontronite of hydrothermal origin has a nearly monomineralic character, a low Al-content, and a formation temperature of 21.5 to 67.3°C. The most remarkable characteristic, however, of the nontronite deposit is its microstructure, a network of microtubes composed of fine frequently folded clay sheets. These delicate filaments show close similarity in size and form to sheath forming bacteria. The correlation between clay mineral and chemical characteristics, as well as biological conditions at marine hydrothermal smoker chimneys, let us suggest that Fe oxidizing, sheath forming bacteria are playing a decisive role in nontronite formation at these sites.
Infrared Spectroscopic Analyses on the Nature of Water in Montmorillonite
Authors: Bishop Janice L. , Pieters Carlé M. , Edwards John O. 
Published: August 2006

AbstractInterlayer cations and moisture content greatly influence the molecular vibrations of H2O in montmorillonite as shown through reflectance spectroscopy in the infrared. The absorptions due to H2O have been studied in montmorillonites exchanged with H, Na, Ca, Mg and Fe3+ interlayer cations under variable moisture environments. Band assignments have been made for absorptions in the 3 µm region due to structural OH vibrations, symmetric and asymmetric H2O stretching vibrations and the H2O bending overtone. Changes in the energies of the absorptions due to H2O stretching vibrations were observed as the samples were dehydrated by reducing the atmospheric pressure. Absorptions near 3620 cm−1 and 3550 cm−1 have been assigned to water bound directly to cations (inner sphere) and surface-bonded H2O and absorptions near 3450 cm−1 and 3350 cm−1 have been assigned to additional adsorbed water molecules. Band assignments have been made for combination bands in the near-infrared as well. Absorptions near 1.41 μm and 1.91 μm are assigned to bound H2O combination bands, while the shoulders near 1.46μm and 1.97 μm are assigned to combinations of additional H2O molecules adsorbed in the interlayer regions and along grain surfaces.
Acid Hydrolysis of Octahedral Mg2+ Sites in 2:1 Layered Silicates: An Assessment of Edge Attack and Gallery Access Mechanisms
Authors: Kaviratna Hemamali , Pinnavaia Thomas J. 
Published: August 2006

AbstractThe acid hydrolysis products of trioctahedral fluorohectorite and phlogopite have been investigated by XRD, MAS NMR spectroscopy and nitrogen BET surface area analysis in an effort to assess the relative importance of edge attack and gallery access mechanisms. A dramatic loss of X-ray crystallinity and the formation of Q3 and Q4 SiO4 sites accompanied the depletion of Mg2+ from the octahedral sheet of both 2:1 layered structures. Depending on the extent of hydrolysis, the products derived from fluorohectorite exhibited surface areas up to 208 m2/g, whereas phlogopite hydrolysis products gave values <20 m2/g. The dramatic differences in surface areas were not related to differences in hydrolysis mechanisms. 19F MAS NMR studies indicated that the hydrolysis of fluorohectorite occurred primarily by an edge attack mechanism equivalent to the hydrolysis pathway for phlogopite. A gallery access mechanism contributed to the hydrolysis of fluorohectorite only at the later stages of octahedral Mg2+ depletion. Solvation effects appeared to be important in determining the surface areas of the reaction products derived from the swelling (fluorohectorite) and non-swelling (phlogopite) precursors.
Acid Activation of a Ferrous Saponite (Griffithite): Physico-Chemical Characterization and Surface Area of the Products Obtained
Authors: Vicente Rodriguez M. A. , Suarez Barrios M. , Lopez Gonzalez J. D. , Bañares Muñoz M. A. 
Published: August 2006

AbstractA ferrous saponite (griffithite) from Griffith Park (California, USA) was treated with solutions of HCl (0.62, 1.25 and 2.5% by weight) at 25°C for 2, 6, 24 and 48 hours. The resulting solids were characterized by XRD, FT-IR spectroscopy, thermal analyses, SEM, TEM and nitrogen adsorption isotherms at 77 K, showing the destruction of silicate structure by the treatments. The free silica generated by these treatments was digested and determined in all samples. Several samples had specific surface areas up to 250 m2/g, with maximum values which are 10 times higher than the surface area of natural saponite (35 m2/g). A sudden decrease in specific surface areas was observed when free silica was digested, which indicates that free silica makes a very important contribution to the surface area of leached samples.
Ferrihydrite: Surface Structure and Its Effects on Phase Transformation
Authors: Zhao Jianmin , Huggins Frank E. , Feng Zhen , Huffman Gerald P. 
Published: August 2006

AbstractX-ray absorption fine structure (XAFS) spectra were collected on a series of ferrihydrite samples prepared over a range of precipitation and drying conditions. Analysis of the XAFS pre-edge structures shows clear evidence of the presence of lower coordination sites in the material. These sites, which are most likely tetrahedral, are believed to be at the surface and become coordination unsaturated (CUS) after dehydroxylation. With chemisorbed water molecules, the CUS sites become the crystal growth sites responsible for the phase transformation of ferrihydrite to hematite at low temperatures. On the other hand, when impurity anions such as SiO4−4 are present in the precipitation solution, the CUS sites may instead absorb the impurity anions, thereby blocking the crystal growth sites and inhibiting the formation of hematite.
Simultaneous Mineralogical Quantification and Chemical Characterization of Soil Clays
Authors: Laird D. A. , Dowdy R. H. 
Published: August 2006

AbstractA new chemical mass balance technique has been developed for simultaneous mineralogical quantification and chemical characterization of soil clays. The procedure includes separation of the whole clay (<2 μm fraction) into six particle size fractions (<0.02, <0.06, <0.2, 0.02–0.06, 0.06–0.2, and 0.2–2 μm fractions), chemical analysis of the whole clay and each of the six fractions, and fitting of a nonlinear chemical mass balance model to the chemical analyses. As written, the chemical mass balance model is valid only for samples containing mixtures of quartz, kaolinite, illite, and mixed-layered smectiteillite. Samples containing carbonates and free iron compounds may be analyzed using the technique if these phases are chemically removed prior to particle size fractionation. Accuracy of the new technique was tested using synthetic data and found to depend on the quality of the input data; however, clay phase quantification within three percentage points of known values was readily achieved. Precision of the technique was evaluated by independently preparing and analyzing five samples of the same soil clay. Standard deviations for clay phase percentages (w:w) in the <2 μm fraction were all less than one percent. The new technique yields accurate determinations of chemistry for the smectitic and illitic phases in mixed-layered smectiteillite, and qualitative estimates for the chemistry of 10 Å-illite. The elemental compositions of quartz and kaolinite are assumed a priori and treated as constants within the non-linear chemical mass balance model.
Mineralogy of Rhizospheric and Non-Rhizospheric Soils in Corn Fields
Authors: Kodama Hideomi , Nelson Sherman , Yang Ann Fook , Kohyama Norihiko 
Published: August 2006

AbstractTechnical limitations have restricted investigations of rhizosphere mineralogy. Various analytical techniques were applied to assess root-mineral associations and dynamics in natural soils under corn production. Soil samples were collected between four and five weeks after planting and included rhizospheric and non-rhizospheric soils, and undisturbed block samples containing corn root systems. Analytical techniques were applied and included; X-ray diffraction, optical microscope, SEM, EDXRA with SEM, transmission electron microscope (TEM), electron energy loss spectra with TEM, high-resolution transmission electron microscope (HRTEM) and microanalysis with HRTEM. The mineralogy of the rhizosphere differed from that of the bulk soil. Within the rhizosphere, minute platy particles which were mostly vermiculitic minerals, were particularly concentrated near or on root surfaces. These platy mineral particles were not attached to the entire area, but only to certain areas of root surfaces. Therefore, we report quantitative evidence for mineralogical changes in the rhizosphere in soil environments.
Mössbauer Spectroscopic Evidence for Citrate-Bicarbonate-Dithionite Extraction of Maghemite from Soils
Authors: Singer M. J. , Bowen L. H. , Verosub K. L. , Fine P. , TenPas J. 
Published: August 2006

AbstractIn a previous paper, we used powder X-ray diffraction and changes in magnetic susceptibility to argue the importance of pedogenic maghemite to soils and the efficacy of the chemical extractant citrate-bicarbonate-dithionite (CBD) to preferentially remove pedogenic maghemite from soil samples while not removing coarse-grained magnetite. Although X-ray diffraction provides strong support for this contention, Mössbauer spectroscopy is the method of choice for determining the oxidation state of iron in minerals and for inferring mineralogy of the iron oxide phases. Our objective in this work was to seek confirming evidence of the importance of maghemite as a pedogenic mineral and the usefulness of the CBD procedure in separating pedogenic maghemite from lithogenic magnetite. We present Mössbauer data on magnetic fractions from pre- and post-CBD treated soil samples. Six of the 10 samples had only maghemite as the sextet component and after CBD treatment, four lost between 96 and 100% of the magnetic susceptibility. Two samples were interpreted as highly oxidized magnetite or a mixture of magnetite and maghemite. We cannot distinguish between these with Mössbauer spectroscopy. In the remaining two samples, iron existed as hematite, ilmenite, magnetite and minor (<10%) amounts of maghemite. Our results provide additional support for pedogenic maghemite in soils and for the preferential removal of maghemite by the CBD procedure.
The Electronic Structure of the Cronstedtite Layer
Authors: Benco Ľubomír , Smrčok Ľubomír 
Published: August 2006

AbstractThe bonding in a cronstedtite layer was studied using a ninefold ordered supercell band structure calculation. The tight-binding scheme based upon the extended Hückel method was used to predict the electronic structure. The size of the problem was 162 atoms with 798 valence orbitals. The calculation showed different orbital interactions of oxygen p-orbitals with neighboring atoms with respect to the position in the layer. Substitution of Fe for Si in the terahedra reduced the role of the valence p-orbitals of the central Fe atoms. The d-orbitals of Fe were split in accordance with the rule of t2g-eg splitting. Although the density of states at the Fermi level was high, the partially filled 3d-bands were too narrow to permit normal metallic conduction.