bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crystal Structure of a Vermiculite-Anilinium Intercalate
Authors: Slade P. G. , Dean C. , Schultz P. K. , Self P. G. 
Published: August 2006

AbstractIf anilinium ions are intercalated into Llano vermiculite, the stacking order of adjacent silicate layers is increased, resulting in a relatively sharp single crystal X-ray diffraction (XRD) pattern. The packing of intercalated organic members forms a superstructure and produces bonding from layer to layer which favors the stacking order. Superlattice reflections occur which, although sharp in the a*b* plane, are streaked along c*. Apparently there is little coherence between adjacent layers of ordered organic units.A three-dimensional set of XRD reflections for a triclinic sub-cell having the following lattice parameters was measured: a = 5.326(3), b = 9.264(4), c = 14.82(5) Å, α = 90.31(7), β = 96.70(6), and γ = 89.55(5)°. In this unit cell (symmetry Cl), ditrigonal cavities in adjacent silicate layers are approximately opposite. Differential Fourier analyses and least-squares refinements showed that the principal axes of the anilinium ions, i.e., N-C(1)-C(4), are nearly perpendicular to the silicate layers. The planes of the aromatic rings, however, are about ±30° to X, neither parallel nor perpendicular to that direction, as indicated by earlier studies.Inorganic cations and water molecules are also present in the interlayer; the former and some of the latter occupy sites near the middle of the layer. Anilinium-rich and anilinium-poor domains coexist. In the latter, the cation-water system predominates and apparently conforms to the superstructure. Although the cation-water structure could not be uniquely established from the reflections produced by the sub-cell, possible positional coordinates were obtained. From structural data for the silicate layers, no evidence was found for long-range Si/Al ordering in the tetrahedral sites.
Characterization of Overgrowth Structures Formed Around Individual Clay Particles During Early Diagenesis
Authors: Steinberg Michel , Holtzapffel Thierry , Rautureau Michel 
Published: August 2006

AbstractThe coarse (0.4–2 µm) clay fraction of an Albian black shale collected in the Atlantic Ocean (Deep Sea Drilling Project leg 11) consists chiefly (90–95%) of smectite and 5–10% illite. Both minerals are locally surrounded by overgrowth structures, such as fine laths about 0.05–0.4 µm long and 0.02–0.1 µm wide. Individual laths or assemblages of laths protrude from the center of smectite flakes at angles of about 60° to each other. Laths occur around illite crystals in a similar manner or coalesce into a rim that consists of 0.05–0.1-µm-size particles. On the basis of scanning transmission electron microscopy: (1) the center of individual illite crystals consists of a dioctahedral mineral, but the overgrowth structures are Al-Fe beidellites; and (2) the smectite flakes have highly variable compositions, but correspond chiefly to Fe-Al-beidellite, whereas the overgrowths are compositionally close to montmorillonite.The overgrowth structures seem to have formed during early diagenesis. The chemical composition of overgrowths around illite and smectite tend to be similar in response to the new environment, implying an addition of silica to both materials.
Hydrothermal Treatment of Smectite, Illite, and Basalt to 460°C: Comparison of Natural with Hydrothermally Formed Clay Minerals
Authors: Yau Yu-Chyi , Peacor Donald R. , Essene Eric J. , Lee Jung H. , Kuo Lung-Chuan , Cosca Michael A. 
Published: August 2006

AbstractWyoming bentonite, Fithian illite, and basalt from the Umtanum Formation, Washington, were treated hydrothermally at 200° to 460°C and 260 to 500 bars for 71 to 584 days. No change was detected for the bentonite and basalt, except for the loss of calcite and exchange of Ca for K in the smectite and the growth of a small amount of smectite (presumably from a glass phase) in the basalt. Calcite in the initial bentonite may have stabilized the smectite by Ca/K exchange; thus, if the latter is used as a packing material in a nuclear waste repository, limestone should be added. No change was detected in the illite samples treated <300°C; however, at 360°C, euhedral crystals of berthierine and illite grew at the expense of original illite/smectite, apparently by a solution-crystallization process. Significant changes involving the dissolution of starting phases and the formation of illite and chlorite were also detected in mixtures of basalt and bentonite at 400°C; at temperatures <400°C, no changes were observed.The newly formed mineral phases (berthierine, illite, and chlorite) observed by transmission electron microscopy showed euhedral to subhedral shapes. These shapes are the same as those observed in hydrothermally altered sediments from the Salton Sea field and different from those from burial metamorphic environments, such as Gulf Coast sediments. The reaction mechanism is apparently the dissolution of reactants followed by the crystallization of products from solution, without conservation of structural elements of the reactants. Reactions apparently required temperatures greater than those for analogous changes in nature, suggesting that the degree of reaction was controlled by kinetics. The lack of dissolution in experimental runs at low temperatures, however, does not necessarily imply long-term stabilities of these clay minerals.
Authigenesis of Kaolinite and Chlorite in Texas Gulf Coast Sediments
Authors: Burton J. H. , Krinsley D. H. , Pye K. 
Published: August 2006

AbstractCore cuttings from numerous wells traversing Oligocene through Recent sediments of the Texas Gulf Coast were examined with a scanning electron microscope using the back-scattered electron imaging mode (BSE) to ascertain diagenetic changes in clays and associated minerals of mudrocks and of adjacent sandstones. Several occurrences of authigenic kaolinite and chlorite were noted, each characterized by a specific texture and a specific diagenetic microenvironment. In all occurrences kaolinite appears to have formed before chlorite, and in some the kaolinite appears to have precipitated directly from solution. Chlorite, ubiquitously an iron-rich variety, appears to have precipitated in some places directly from solution. It has also been noted pseudomorphous after kaolinite. A progressive decrease in the iron content of mixed-layer illite/smectite with increasing depth is believed to have released the necessary iron and to have driven the kaolinite-to-chlorite reaction.
Effect of Exchangeable Potassium on the Hydraulic Conductivity of Smectite-Sand Mixtures
Authors: Shainberg I. , Keren R. , Alperovitch N. , Goldstein D. 
Published: August 2006

AbstractChanges in hydraulic conductivity of smectite-sand mixtures (using four reference smectites) as a function of the concentration (0.01, 0.003, 0.002, 0.001 M Cl- and distilled water) and potassium adsorption ratio (of 2, 4, and 6) of the percolating solution were measured. Swelling and dispersion of the clays were evaluated from the changes in hydraulic conductivity of the mixture and from the clay concentration in the effluent.The effect of exchangeable potassium percentage (EPP) on the hydraulic conductivity of the smectites depended on the charge density of the clays. The effect of potassium at EPPs <20 on the hydraulic conductivity of smectites having high charge density was negligible. Conversely, the hydraulic conductivity of smectites having low charge density (smectites from Wyoming and Belle Fourche, South Dakota), changed markedly when leached with dilute solutions as the EPP of the clay increased. The dispersive effect of exchangeable potassium on low-charge smectites was similar to that of exchangeable sodium. The low hydration energy of the K+ cations, coupled with the strong electrostatic attraction forces between platelets of smectites with high charge density account for the “inefficiency” of K+ in dispersing these smectites.
Optical Density of Vertisol Clay Suspensions in Relation to Sediment Volumes and Dithionite-Citrate-Bicarbonate-Extractable Iron
Authors: Ben-Dor Eyal , Singer Arieh 
Published: August 2006

AbstractClay fractions of eight vertisols and vertisolic soils from Israel were found to consist principally of a Fe-rich beidellite. Sediment volumes of Na-clay suspensions, obtained in measuring cylinders and read every 24 hr for as long as 720 hr, ranged from 3.8 to 8.4 cm/l00 mg clay and were as much as 19 times larger than corresponding suspensions of Ca-clays. Optical density data for all clay suspensions showed absorption curves typical of smectite. The relative number of platelets per tactoid, calculated from optical density measurements, ranged between 1.4 and 5.4 for the Na-clays and between 7.4 and 14.1 for the Ca-clays. In the Ca-clays, the sediment volume decreased with an increase in the relative number of platelets per tactoid. With increase in the major dimension of particles (calculated also from optical density curves), sediment volume tended to increase for the Na-clays and decrease for the Ca-clays. These relationships can be explained on the basis of particle arrangement patterns: face-to-face arrangements dominated the Ca-clays and edge-to-edge and edge-to-face arrangements dominated the Na-clays. The amount of iron extractable in dithionite-citrate-bicarbonate (DCB) correlated positively with the relative number of plates per tactoid and with the major dimensions of the particles in the Ca-clay suspensions. This correlation suggests that DCB-extractable iron affects the tactoid dimensions of Ca-clays from vertisols and, therefore, may also affect structural properties of vertisols.
Vapor-Phase Sorption Kinetics for Tetrahydrofuran, Tetrahydropyran, and 1,4-Dioxan by Al3+- and Cr3+-Exchanged Montmorillonite
Authors: Breen C. , Deane A. T. , Flynn J. J. 
Published: August 2006

AbstractThe rate of vapor-phase sorption of tetrahydrofuran (THF), tetrahydropyran (THP), and 1,4-dioxan (DIOX) onto a Wyoming montmorillonite saturated with Al3+ or Cr3+ has been studied by isothermal gravimetry in the temperature range 18° to 105°C using samples of different weights and grain-size distributions. The rate of sorption for all the cyclic ethers increased with decreasing sample and grain size, demonstrating that inter-, rather than intraparticle mass transfer was rate-determining. Optimization of the sample parameters (2 mg sample of <45-μm grain size, pretreated at 120°C yielded integral diffusion coefficients at 18°C of 0.5 × 10−14 m2/s for DIOX for the Cr3+-clay to 3.5 × 10−4 m2/s for THF for the Al3+-clay; however, no temperature or cationic dependence of the cyclic ether uptake was observed. In general, the rate of sorption of the cyclic ethers increased as THF ≥ THP > DIOX indicating that the sorption rate of THF and THP was dependent on concentration or that DIOX sorption was retarded by bidentate coordination to aluminum ions at the edges of the clay platelets.
Interpretation of Mössbauer Spectra of Nontronite, Celadonite, and Glauconite
Authors: Daynyak Lydia G. , Drits V. A. 
Published: August 2006

AbstractA new approach to the interpretation of Mössbauer spectra of Fe3+-phyllosilicates having vacant trans-octahedra is based on (1) crystal structure simulation methods that allow for the size and the shape of a Fe3+-octahedron as a function of the nearest surrounding cations; and (2) calculations of electric field gradients (EFG) on Fe3+ in terms of the ionic point-charge model. Calculations were performed by direct summation within the region of radius ≤50 Å. Coordinates for the anions in the coordination octahedra have been assigned to take into account the nearest cationic environment. Atomic coordinates for the rest of the summation volume are those for the average unit cell. EFG calculations for cation combinations responsible for the visible quadrupole splitting Δvis in the spectra of nontronite, “red” muscovite, and celadonite have led to good agreement between Δvis and Δcalc. Computer fitting of the nontronite and celadonite spectra based on EFG calculations for the rest of the possible cation combinations suggests that the distribution of tetrahedral cations in nontronite obeys the Loewenstein rule, and in celadonite, the distribution of R3+ and R2+ over cis-octahedra is predominantly ordered, in agreement with electron diffraction and infrared spectroscopy data. The Mössbauer spectrum of one of the glauconites suggested the presence of celadonite-like and muscovite-like domains in its 2:1 layers.
Intervalence Electron Transfer and Magnetic Exchange in Reduced Nontronite
Authors: Lear Paul R. , Stucki Joseph W. 
Published: August 2006

AbstractThe effects of chemical reduction of structural Fe3+ in nontronite SWa-1 (ferruginous smectite) on intervalence electron transfer (IT) and magnetic exchange were investigated. Visible absorption spectra in the region 800-400 nm of a chemical reduction series of the SWa-1 nontronite revealed an IT band near 730 nm (13,700 cm−1). Both the intensity and position of this band were affected by the extent of Fe reduction. The intensity increased until the Fe2+ content approached 40% of the total Fe, then decreased slightly with more Fe2+. The position of the band also shifted to lower energy as the extent of reduction increased.Variable-temperature magnetic susceptibility measurements showed that the magnetic exchange in unaltered nontronite is frustrated antiferromagnetic, but ferromagnetic in reduced samples. Magnetic ordering temperatures are in the range 10–50 K, depending on the extent of reduction. The ferromagnetic component in the magnetization curve increased with increasing Fe2+ in the crystal structure. The positive paramagnetic interaction likely is due to electron charge transfer from Fe2+ to Fe3+ through such structural linkages as Fe2+-O-Fe3+ (perhaps following a double exchange mechanism), which is consistent with the visible absorption spectra.
Cation-Exchange Properties of (Al + Na)-Substituted Synthetic Tobermorites
Authors: Komarneni Sridhar , Breval Else , Miyake Michihiro , Roy Rustum 
Published: August 2006

AbstractTobermorite, Ca5Si6O16(OH)2·4H2O, is a hydrous calcium silicate that has a layer-type of structure similar to that of the 2:1 clay minerals. In its natural form, tobermorite exhibits little or no exchange for alkali cations; synthetic tobermorites, however, exhibit reversible alkali cation exchange and selective cesium uptake upon a coupled substitution of (Al3+ + Na+) for Si4+. Substituted tobermorites were synthesized using aluminosilicate gels, NaOH, and CaO, in Parr bombs at 175°C for 4 days. Unsubstituted tobermorite was synthesized using quartz and CaO in a Parr bomb at 175°C for 20 hr. Two (Al + Na)-substituted tobermorites showed cation-exchange capacities (CEC) of 77 and 71 meq/100 g, whereas an unsubstituted tobermorite showed a CEC of 12 meq/100 g. The substituted tobermorites exhibited selective Cs exchange from either NaCl or CaCl2 solutions. For example, one substituted tobermorite showed a Cs-exchange coefficient (Kd) of 15,100, whereas unsubstituted tobermorite showed a Kd of only 90 from a 0.02 N CaCl2 solution containing 0.0002 moles/liter CsCl. Exchange isotherms for Na+ ⇋ Cs+ showed that Cs+ is preferred over Na+ throughout the exchange in the (Al + Na)-substituted tobermorites. This group of cation exchangers is expected to find applications in radioactive waste disposal.
Optically Selective Adsorption of α-Amino Acids on Montmorillonite-Cu-1-Lysine Complexes in High-Pressure Liquid Chromatography
Authors: Tsvetkov Faina , Mingelgrin U. 
Published: August 2006

AbstractOptically active cationic complexes adsorbed on montmorillonite can be used for the resolution of racemic mixtures. Montmorillonite-Cu-lysine systems were used as a solid phase in high-pressure liquid chromatography for the resolution of the optical isomers of α-amino acids. Selectivity constants > 1.5 were measured for phenylalanine and tryptophan. The selectivity constants for the amino acids containing saturated-hydrocarbon side chains were in the range of 1.25–1.44. The montmorillonite-Cu-l-lysine complex displayed a stronger affinity for the l-isomers of α-amino acids than for the d-isomers at pHs near neutrality. Inasmuch as surface-catalyzed peptide formation on clays has been proposed as a step in chemical evolution, this stronger affinity between the clay-Cu-l-amino acid complex and l-amino acids might have been significant in prebiotic evolution. The mechanism of optical resolution probably involved ligand exchange. Optimizing the choice of the optically active ligands and of the chelating cation in the chiral agent may improve the resolution of the optical isomers.
Diagenetic Alteration of Silicic Ash in Searles Lake, California
Authors: Hay Richard L. , Guldman Sandra G. 
Published: August 2006

AbstractAsh layers from Searles Lake, California, were sampled in core of drill hole KM-3, which penetrated 693 m of lacustrine sediment deposited in a playa-lake complex over the past 3.2 my. Lake water changed from moderately saline and slightly alkaline (pH ~7.5) to highly saline 2.04 my ago and to highly saline and alkaline (pH ~9.5) 1.28 my ago. As a result of brines flushing downward, the upper 291 m of sediment, spanning the past 1.28 my, contain highly saline, alkaline pore fluid. Silicic ash layers in contact with highly saline, alkaline pore fluid were first altered to phillipsite and meriinoite and then to K-feldspar and searlesite. The transformation of phillipsite and/or meriinoite to K-feldspar required more than 45,000 years and was largely completed in 140,000 years. Tephra layers in contact with moderately saline, slightly alkaline pore fluid vary from uncemented vitric ash containing minor smectite to bentonites in which glass is wholly altered to smectite, clinoptilolite, analcime, and opal. Layers with much fine tephra are more altered than the coarser, better-sorted layers. Alteration is attributed to hydrolysis in essentially a closed hydrologic system, in which the alteration of glass to smectite raised the pH, aSiO2, and (Na+ + K+)/H+ activity ratio to the level where clinoptilolite formed. Some diffusion and/ or fluid flow is, however, indicated by the loss of SiO2 during the alteration of ash layers to smectite and by anhydrite deposited during and after clinoptilolite in some tuffaceous sandstones.
Sodium, Calcium, and Ammonium Exchange on Clinoptilolite from the Fort Laclede Deposit, Sweetwater County, Wyoming
Authors: Hulbert Matthew H. 
Published: August 2006

AbstractClinoptilolite from the Fort LaClede deposit in Sweetwater County, Wyoming, shows a moderate selectivity for NH4− over Na+ in aqueous solution. At 30°C, the standard free energy of this replacement reaction is −0.7 kcal/mole at an ionic strength of 0.05 M and −0.8 kcal/mole at 0.5 M. The Na+-NH4+ exchange is complete within 3 days in agitated solution and proceeds to the same extent from the clinoptilolite saturated with either cation.The Ca2+-Na+ exchange also is complete within 3 days in agitated aqueous solution and proceeds to the same extent from either the calcium or the sodium form of the zeolite. Using test methods which take into account the slower equilibration of Ca2+-loaded clinoptilolite, the cation-exchange capacity is substantially the same over the full range of loading by Ca2+ and Na+. Ca2+ replaces Na+ with decreasing selectivity as Ca2+ loading increases to about 80% at 30°C (95% at 63°C), above which the selectivity reverses. The standard free energy of replacement of two Na+ ions by one Ca2+ ion in 0.05 M solution is −1.2 ± 0.2 kcal/mole at 63°C and −0.3 to −0.8 kcal/mole at 30°C.
Transmission Electron Microscope Study of Biotite Weathering
Authors: Banfield Jillian F. , Eggleton Richard A. 
Published: August 2006

AbstractTransmission electron microscopy suggests that biotite transforms to vermiculite primarily by direct structural modification, involving the replacement of K+ by hydrated interlayer cations, and only minor reorganization of the 2:1 layer. A second relatively uncommon mechanism appears to involve redistribution of components from two biotite sheets to form a single vermiculite layer. Distortion of the surrounding structure initially inhibits growth of vermiculite in the surrounding biotite, and promotes the propagation of vermiculite layers in opposite directions. This phenomenon may contribute to the development of relatively regular, widely spaced interstratifications of biotite and vermiculite. Additional components and space are provided by the dissolution of biotite where access of solutions is greater.During weathering, biotite and vermiculite become increasingly replaced by kaolinite, which crystallizes epitactically onto existing layers, and goethite, which develops from a poorly crystalline iron oxyhydroxide precursor to form oriented laths. In areas parts of strongly weathered samples kaolinite and goethite appear to develop in proportions consistent with a reaction that conserves both Al and Fe.
Investigation of a K-Bentonite by X-Ray Powder Diffraction and Analytical Transmission Electron Microscopy
Authors: Huff W. D. , Whiteman J. A. , Curtis C. D. 
Published: August 2006

AbstractThe <0.1-μm size fraction of an Ordovician K-bentonite from northern Kentucky was characterized by X-ray powder diffraction (XRD). Using A.I.P.E. A. criteria for interstratification nomenclature and Reynolds’ computer algorithm the dominant clay mineral proved to be an R2 ordered illite/smectite. The best fit of observed and calculated XRD tracings was obtained using 12 > N > 5, where N is the number of layers within a diffracting domain.Sections of the K-bentonite were prepared by ion-beam milling and examined in an analytical transmission electron microscope (ATEM). One-dimensional lattice images observed parallel to the a-b plane showed subparallel packets, about 50–100 Å thick, each of which consisted of about 10-Â thick unit layers. Somewhat thicker unit layers (as much as 14.5 Å) were also seen. The former are presumed to be illite, whereas the latter may be partially collapsed smectite. Selected-area electron diffraction patterns suggested simultaneous diffraction from several packets, each containing at least five layers. Both h0l and 0kl spacings were usually present, indicating that the stacking of the subparallel packets was random. Quantitative analysis by AEM and electron microprobe show the clay to be low in tetrahedral Al but high in octahedral Mg, the latter presumably contributing largely to the interlayer charge responsible for K fixation. The TEM data are broadly reconcilable with the accepted XRD interpretation of a two-component, mixed-layer clay. Alternatively, the TEM images may be interpreted as a single phase having numerous packet boundaries, the latter being responsible for swelling behavior. These two interpretations will not be fully reconciled until greater analytical precision and resolution permit individual packets to be studied. This work suggests that mineral definitions based purely on XRD interpretations may have to be reconsidered as more electron microscope data become available.