bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reactions of Polynuclear Hydroxyaluminum Cations with Montmorillonite and the Formation of A 28-Å Pillared Complex
Authors: Singh S. Shah , Kodama H. 
Published: August 2006

AbstractPolynuclear hydroxy-Al cations were prepared by partially neutralizing dilute solutions of aluminum chloride. These cations were introduced in the interlayer space of montmorillonite by cation exchange, which formed heat-stable pillars between the silicate layers. Polynuclear hydroxy-Al was preferentially adsorbed on montmorillonite compared with monomer-Al; the maximum amount adsorbed was ∼400 meq/100 g of montmorillonite. Of this amount 320 meq was non-exchangeable. The 001 X-ray powder diffraction reflection of the polynuclear hydroxy-Al-montmorillonite complex was at 27 Å, with four additional higher-order basal reflections, giving an average d(001) value of 28.4 Å. This complex was thermally stable to 700°C. An analysis of the basal reflections by the Fourier transform method indicated that the 28-Å complex had a relatively regular interstratified structure of 9.6- and 18.9-Å component layers with a mixing ratio of 0.46:0.54. This ratio implies that the hydroxy-Al pillars occupied every second layer. Considering the relatively small amount of Al adsorbed and the thermally stable nature of the structure, the hydroxy-Al pillars must have been sparsely but homogeneously distributed in the interlayer space.
Effect of Magnesium on the Hydraulic Conductivity of Na-Smectite-Sand Mixtures
Authors: Shainberg I. , Alperovitch N. , Keren R. 
Published: August 2006

AbstractChanges in hydraulic conductivity (HC) and clay dispersion of smectite-sand mixtures as a function of exchangeable Na in Na-Ca and Na-Mg systems were measured. The charge density on the smectites had no effect on Na-Ca and Na-Mg equilibrium, and the affinity of the clays for Na was similar in both systems. A decrease in HC at 0.01 M concentration was found to be due to clay swelling. Mg was found to be less effective than Ca in preventing the breakdown of the packets by low concentrations of exchangeable Na, and Na-Mg-smectite swelled more than Na-Ca-smectites.Na-Mg-clay particles dispersed more readily than Na-Ca-clay particles when the mixtures were leached with distilled water; however, if the electrolyte concentration in the clay-sand mixture was controlled by the leaching solutions, no difference between the Na-Mg- and Na-Ca-clays was noted. Thus, the effect of Mg on clay mixtures leached with distilled water was apparently due to the effect of Mg on the hydrolysis of the clays. Increase in charge density increased the stability of the R2+ clay packets, and higher concentrations of Na were needed to break the packets. Mg was less effective than Ca in stabilizing the packets, and lower concentrations of Na were needed to break the Mg-packets.
Stacking Order in a 14.30-Å Mg-Vermiculite
Authors: de la Calle Cristina , Suquet Hélène , Pons Charles-Henri 
Published: August 2006

AbstractThe stacking order of a 14.30-Å Mg-vermiculite from Santa-Olalla, Spain, has been determined from Weissenberg photographs. The results prove that the Mg-vermiculite structure is not a 2-layer polytype structure, but a semi-ordered one. Because the structure is semi-ordered, its resolution needed a dual approach: (1) a direct approach using an electron density projection along the y axis in conjunction with a one-dimensional electron-density projection onto the z axis; and (2) an indirect approach in which the observed intensities along the (0,k) and (1,k) reciprocal rods were compared to the calculated intensities given by model defect structures. The semi-ordered structure of the Mg-vermiculite results from ±b/3 shifts in the stacking of the silicate layers. The shifts are randomly either along +b or -b.
Analytical Electron Microscopy and the Problem of Potassium Diffusion
Authors: van der Pluijm Ben A. , Lee Jung Hoo , Peacor Donald R. 
Published: August 2006

AbstractDiffusion of K during analytical electron microscopy (AEM) results in anomalously low count rates for this element. As the analysis area and specimen thickness decrease, count rates become disproportionally lower. Adularia and muscovite show different diffusion profiles during AEM; for muscovite a strong dependence of diffusion on crystallographic orientation has been observed. Conditions giving rise to reliable chemical data by AEM are the use of a wide scanning area (>800 × 800 Å) and/or large beam size to reduce the effect of diffusion of alkali elements, a specimen thickness greater than about 1000 Å, constant instrument operating conditions, and the use of a homogeneous, well-characterized standard sample. The optimum thickness range was obtained by determining the element intensity ratio vs. thickness curve for given operating conditions. The standard and unknown should have a similar crystal structure and, especially for strongly anisotropic minerals such as phyllosilicates, a similar crystallographic orientation with respect to the electron beam.
Hydrothermal and Supergene Alterations in the Granitic Cupola of Montebras, Creuse, France
Authors: Dudoignon P. , Beaufort D. , Meunier A. 
Published: August 2006

AbstractA mineralogical investigation of the highly kaolinized Chanon granite and albite-muscovite granite of the Montebras cupola, Creuse, France, indicates that the magmatic stage was followed by two hydrothermal events related to successive cooling stages and by late weathering. The hydrothermal alteration was accompanied first by greisen formation and then a broad kaolinization process, which pervasively affected the granitic bodies. In the Chanon granite, the greisens are characterized by a trilithionite-lepidolite-quartz-tourmaline assemblage and are surrounded by concentric alteration zones. From the greisen to the fresh granite three zones were distinguished: (1) a zone characterized by secondary brown biotite (<400°C), (2) a zone characterized by secondary green biotite and phengite (300–350°C), and (3) a zone characterized by the presence of corrensite (180°–200°C) located around greisen veinlets. In the albite-muscovite granite the greisen is composed of lepidolite and quartz. This mineral assemblage was followed locally by Li-tosudite crystallization. During the second hydrothermal event (<100°C) an assemblage of kaolinite, mixed-layer illite/smectite (I/S), and illite formed pervasively and in crack fillings; the smectite layers of the US are potassic. Weathering produced Fe oxide and kaolinite. This kind of alteration developed mainly in the overlying Chanon granite. Here, Ca-Mg-montmorillonite formed in subvertical cracks, which transect the two granitic bodies, and hydrothermal I/S was obliterated by Ca-Mg-montmorillonite.The hydrothermal parageneses were apparently controlled by magmatic albitization and the bulk chemistry of the two granitic bodies. The albitization, the formation of large micaceous greisens, and the successive recrystallizations of biotite (which was the most susceptible phase to alteration) provide information on the temperature range and chemical mobility during successive cooling stages. Si and Mg activities increased as the temperature of alteration decreased, and secondary Mg-biotite and Mg-phengite crystallized as long as the K activity was sufficient. The crystallizations of secondary biotite and phengite were followed by the crystallization of I/S during stages of low K activity. Secondary hydrothermal phases in the Chanon granite contain substantial Fe and Mg. Secondary hydrothermal phases in the albite-muscovite granite contain only small amounts of Fe and Mg, suggesting a lack of chemical exchange between the enclosing Chanon granite and the albite-muscovite granite, which is depleted in Fe-Mg-rich primary phases, such as biotite.
Weathering of Iron-Bearing Minerals in Soils and Saprolite on the North Carolina Blue Ridge Front: II. Clay Mineralogy
Authors: Graham R. C. , Weed S. B. , Bowen L. H. , Amarasiriwardena D. D. , Buol S. W. 
Published: August 2006

AbstractThe mineralogy of the clay fraction was studied for soils and saprolite on two Blue Ridge Front mountain slopes. The clay fraction contained the weathering products of primary minerals in the mica gneiss and schist parent rocks. Gibbsite is most abundant in the saprolite and residual soil horizons, where only chemical weathering has been operable. In colluvial soil horizons, where both physical and chemical weathering have occurred, the clay fraction consists largely of comminuted primary phyllosilicates —muscovite, chlorite, and possibly biotite—and their weathering products: vermiculite, interstratified biotite/vermiculite (B/V), and kaolinite. The clay-size chlorite contains Fe2+ as indicated by Mössbauer spectroscopy, and is more resistant to weathering than biotite. The vermiculite and B/V, both weathering products of biotite, contain Fe3+. Vermiculite in colluvial soils and, especially, surface horizons is weakly hydroxy-interlayered. The kaolinite in the clay fraction resulted at least partly from the comminution of kaolinized biotite in coarser fractions.The hematite content ranged from 0 to 8% of the clay fraction and strongly correlates (r =.95) with dry clay redness, as measured by the redness rating: RR = (10 - YR hue) × (chroma) ÷ (value). The hematite is largely a product of the weathering of almandine; thus, the soil redness is dependent on the amount of almandine in the parent materials and its degree of weathering in the soils. Goethite (13–22% of the clay fraction) imparts a yellow-brown hue to soils derived from almandine-free parent rocks. The release of Fe in relatively low concentrations during the weathering of Fe-bearing primary minerals, particularly biotite, appears to have promoted the formation of goethite.
Diagenetic Alteration of Perlite in the Guryongpo Area, Republic of Korea
Authors: Noh Jin Hwan , Boles James R. 
Published: August 2006

AbstractPerlite, which occurs at the contacts between dacite and lacustrine tuffs of Miocene age in the Guryongpo area, Korea, has undergone more sluggish and incomplete diagenetic alteration than the surrounding zeolitic tuffs. Alkali-clinoptilolite, mordenite, smectite, K-rich gel-like glass, low-cristobalite, and K-feldspar are characteristic diagenetic phases in the altered perlite.Hydration of the glass to form perlite resulted in the expulsion of cations, mainly Na, from the glass into the pore fluid and in the relative enrichment of K in the perlite. Hydration of the glass also resulted in increased alkalinity of the pore fluid, which, in turn, affected the nature and behavior of subsequent glass dissolution. Textural observations and chemical data on the early diagenetic phases indicate a sequence of incongruent dissolution reactions, which depended on silica activity and alkalinity of the ambient pore fluid: Reaction (1) 12.5 perlitic glass + 3.88 K+ + 0.65 H+ + 15.4 H20 = smectite + 9.5 gellike glass + 4.03 Na+ + 0.25 Ca2+ + 10.55 H4SiO4 released Ca and silica which were consumed by reaction (2) perlitic glass + 0.1 Ca2+ + 0.1 H4SiO4 + 0.1 H+ + H20 = clinoptilolite + 0.1 K+ + 0.2 Na+. The paragenesis from glass via smectite to alkali zeolites in most glass-bearing rocks may be explained by a sequence of such dissolution reactions. Still later reactions involved the transition from less-silicic clinoptilolite to an assemblage of silicic Na-clinoptilolite + mordenite and the crystallization of the gel-like glass to K-feldspar.
Oxidation State of Iron in Glauconite from Oxidized and Reduced Zones of Soil-Geologic Columns
Authors: Fanning D. S. , Rabenhorst M. C. , May Leopold , Wagner D. P. 
Published: August 2006

AbstractGlauconite from the oxidized and reduced zones of soil-geologic columns at two Coastal Plain sites, one in Maryland and one in New Jersey, was examined by Mössbauer spectroscopy. The data indicate that glauconite in the reduced zones had a higher proportion of its structural iron in the ferrous, as opposed to the ferric state. The Fe2+/Fe3+ ratio ranged from 0 to 0.2 for the glauconite from the oxidized zone and was about 0.35 for the glauconite in the reduced zones. Despite the presence of pyrite in the reduced zone, which might be expected to make ferric iron unstable because of the presence of sulfide S, about 75% of the Fe in the glauconite in the reduced zone was in the ferric state. Thin section analysis showed some glauconite in the reduced zones to be intimately associated with pyrite and some aggregates of fine pyrite crystals were locally present in cracks in glauconite pellets. In the oxidized zones, pyrite was absent and the glauconite was more yellow under plane-polarized light, as opposed to more green for the glauconite in the reduced zones. These data indicate that reports of studies of glauconite should stipulate whether samples are from the oxidized or reduced zone of soil-geologic columns.
Resolution of the Polytype Structure of Some Illitic Clay Minerals that Appear to Be 1Md
Authors: Austin G. S. , Glass H. D. , Hughes R. E. 
Published: August 2006

AbstractIllite/smectite (I/S) and illite samples that appear to be 1Md polytypes on the basis of the lack of diagnostic reflections can be resolved as partly either 1M or 2M1 or both by either vapor solvation in ethylene glycol for 40 to 80 hr at ambient temperatures or for 4 hr at 80°C, or by heating to 375°C for 2 hr. If samples are so treated, a distinct narrowing of the I/S 003/005 peak occurs and diagnostic hkl reflections are revealed. These treatments, however, do not seem to affect diagnostic polytypic peak intensities, but rather the adjacent background. We propose that the 1Md term be restricted to its original definition—the disordered polytype associated with only the 1M ordered polytype. For illites in which disorder exists with a mixture of polytypes, the generic term Ad (disordered group A micas) should be used. Correct polytype determination of illitic material is significant because it reveals thermal history of the sediments and allows greater understanding of the depositional and diagenetic history of sedimentary basins.
Aqueous-Chemical Control of the Tetrahedral-Aluminum Content Of Quartz, Halloysite, and other Low-Temperature Silicates
Authors: Merino Enrique , Harvey Colin , Murray H. H. 
Published: August 2006

AbstractAqueous Al passes from octahedral to tetrahedral coordination over a narrow pH interval, or threshold. This interval is 5.5–6.5 at 25°C and shifts to lower pH as temperature increases. The concentration of aqueous tetrahedrally coordinated Al is a quasi-step function of the solution pH, and, by the mass-action law, so should be the amount of tetrahedral Al incorporated by a silicate that crystallizes from the aqueous solution. Qualitative support for this prediction (which applies to quartz, opal-CT, kaolin-group minerals, pyrophyllite, micas, chlorites, and other low-temperature silicates) comes from the very topology of equilibrium activity diagrams and from several pairs of associated waters and authigenic silicates from weathering, hydrothermal, and diagenetic environments. The uptake of tetrahedral Al also depends on the aqueous concentrations of monovalent cations and silica, and on the mineral's structural constraints.Solid solution of tetrahedral Al in halloysite in turn produces the characteristic bent or tubular crystals of this mineral. This genetic link between aqueous chemistry (mainly pH), tetrahedral-Al uptake by a low-temperature silicate, and the mineral's crystal morphology may operate also in other silicates.
Mn-Substituted Goethite and Fe-Substituted Groutite Synthesized At Acid pH1
Authors: Ebinger M. H. , Schulze D. G. 
Published: August 2006

AbstractMn-substituted iron oxides were synthesized by coprecipitating Fe(NO3)3 and Mn(SO4) solutions with NH4OH, adjusting the suspensions to pH 4 or 6, and then keeping the suspensions at 55°C for 62 days. The Mn mole fraction of the final products ranged from 0 to 0.3. X-ray powder diffraction patterns showed that goethite and hematite formed in each Fe-containing system. Groutite formed in systems having initial Mn mole fractions ≥0.35. Only manganite and hausmannite formed in the pure Mn systems. The oxalate-soluble Fe in the samples increased as the Mn mole fraction increased and was slightly larger for the pH 6 series.For samples that contained the largest Mn mole fraction, the b and c dimensions of the goethite unit cell were shifted toward those of groutite, and the b and c dimensions of the groutite unit cell were shifted toward those of goethite. Assuming the Vegard rule holds for the unit-cell c dimension, the goethite accommodated a maximum Mn mole fraction of 0.34, and the groutite accommodated a maximum Fe mole fraction of 0.31. The unit-cell dimensions of hematite did not vary systematically with the mole fraction of Mn in solution, probably because little Mn substituted into the hematite structure.
Adsorption and Desorption of N-Methyl 8-Hydroxy Quinoline Methyl Sulfate on Smectite and the Potential Use of The Clay-Organic Product as an Ultraviolet Radiation Collector
Authors: Vicente M. A. , Sánchez-Camazano M. , Sánchez-Martín M. J. , del Arco M. , Martín C. , Rives V. , Vicente-Hernández J. 
Published: August 2006

AbstractThe interaction between N-methyl 8-hydroxy quinoline methyl sulfate, a drug that absorbs erymathogenic near-ultraviolet radiation, and smectite was studied by X-ray powder diffraction (XRD) and adsorption and desorption techniques. From the adsorption studies, (1) the amount of the drug adsorbed by Na-smectite increased with the pH of the solution to pH 6.5 and then decreased as the pH was further increased; (2) the maximum amount adsorbed at pH 6.5 was 102 meq/100 g of clay; and (3) the maximum amount of drug adsorbed, according to the adsorption isotherms at pH 4, was close to the cation-exchange capacity of the smectite (80 meq/100 g). The XRD studies showed that the drug molecules were adsorbed in the interlayer space of smectite and that cation exchange was the chief mechanism responsible for these interactions. The results of the adsorption-desorption cycles of the drug by smectite showed that this clay is a good support for this compound. In addition, an alternative method was developed to obtain the intercalation compound to avoid the standard method of exchange by impregnation. The method consisted of grinding a mixture of the drug with the clay. The characteristics of the complex thus formed were similar to those of the complex formed by exchange at pH 4 to 7.To gain insight into the pharmacological properties of the intercalation compound studied, its capacity for absorption of visible and near-ultraviolet light was investigated. The diffuse reflectance spectrum of the complex showed intense absorption bands, absent or weak in the spectra of the pure drug or the untreated clay, at 250, 290, and ~390 nm.
Clay Mineral Segregation by Flocculation in the Porters Creek Formation
Authors: Thomas Andrew R. , Murray Haydn H. 
Published: August 2006

AbstractThe Porters Creek Formation is mined as an absorbent clay in Illinois, Mississippi, Missouri, and Tennessee. The absorptive properties of the Porters Creek Formation are due to the high content of smectite which constitutes >50% of the minerals present. Analyses of 220 samples of the Porters Creek collected in Illinois, Missouri, and Tennessee indicate that the smectite content is highest on the western side of the Mississippi embayment and that the kaolinite content is highest on the northeastern side. The major influx of detritral clays appears to have entered the embayment from a large river on the northeast side. A major control of the distribution of clay minerals during the time of Porters Creek deposition was differential flocculation of kaolinite, illite, and smectite, as evidenced by the numerous syneresis cracks on bedding planes in the area of greatest kaolinite content. Estimates of the smectite, illite, and kaolinite contents suggest both horizontal and vertical variations among these clay minerals. In certain localities the oxidation of pyrite has created acid conditions, which apparently were conducive to the formation of authigenic halloysite.
Structures of Intergrown Triclinic and Monoclinic IIb Chlorites from Kenya
Authors: Zheng Hong , Bailey Sturges W. 
Published: August 2006

AbstractTriclinic IIb-4 and monoclinic IIb-2 clinochlore polytypes from Kenya are intergrown laterally in (001) platelets and are separated optically in some places by sharp lines of demarcation and in other places by embayed boundaries. Electron microprobe analyses show no compositional differences between the two polytypes. Structural refinements of each show that the 2:1 layer is identical in the two structures with no tetrahedral or 2:1 octahedral cation ordering in either ideal or subgroup symmetries. The two interlayer sheets dilfer only in the distribution of A1 and Mg over interlayer sites M3 and M4, but not in the distribution of Fe3+, Fe2+, or vacancies. The monoclinic IIb-2 polytype is less ordered than the triclinic IIb-4 polytype. The mean M-O,OH bond length of 1.990 Å indicates significantly less of the smaller A1 present in the M4 site of IIb-2 than for the mean M-O,OH value of 1.957 Å for the M4 site of IIb-4. The textural relations and the structural refinements suggest that the monoclinic IIb-2 structure is inherently less stable than the triclinic form. This is in accord with the observed lesser abundance in nature of the monoclinic form.
Structure and Thermal Transformations of Imogolite Studied by 29Si and 27Al High-Resolution Solid-State Nuclear Magnetic Resonance
Authors: MacKenzie K. J. D. , Bowden M. E. , Brown I. W. M. , Meinhold R. H. 
Published: August 2006

AbstractSolid-state nuclear magnetic resonance (NMR) spectroscopy, thermal analysis, and X-ray powder diffraction data on the tubular, hydrous aluminosilicate imogolite were found to be fully consistent with a previously proposed crystal structure consisting of a rolled-up, 6-coordinate Al-O(OH) sheet, bonded to isolated orthosilicate groups. The calculated 29Si chemical shift of this structure agreed with the observed shift within 3 ppm. Thermal dehydroxylation of the Al-O(OH) sheet produced predominantly NMR-transparent 5-coordinate Al, but a few 4- and 6-coordinate sites and some residual hydroxyl groups may also have formed, as shown by NMR spectroscopy. Changes in the 29Si NMR spectrum on dehydroxylation suggest a condensation of the orthosilicate groups, but steric considerations rule out bonding between adjacent silicons. To account for these observations, an alternative mechanism to orthosilicate condensation has been proposed, involving the fracture and unrolling of the tubes, followed by the condensation of fragments to form a layer structure. The layer structure has a calculated 29Si chemical shift of -95.6 ppm, in good agreement with the observed value of -93 ppm.