bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intercalation Method using Formamide for Differentiating Halloysite from Kaolinite
Authors: Churchman G. J. , Whitton J. S. , Claridge G. G. C. , Theng B. K. G. 
Published: August 2006

AbstractA rapid and simple test to distinguish halloysite from kaolinite in mineral mixtures has been developed based on differences in the rate and extent of formamide intercalation. With halloysite, complex formation was both rapid (<1 hr) and complete, whereas no significant intercalation occurred with kaolinite until at least 4 hr after contact with formamide, and then the process may not have been complete. Unheated halloysite formed complete complexes with formamide regardless of the interlayer hydration state of the mineral. The test, however, was inconclusive for halloysite that had been oven-dried at 110°C, although some water may still have been present in the interlayer space. The extent of formamide intercalation by kaolinite was likely influenced by sample crystallinity, and the rate of complex formation was enhanced by the addition of up to 10% v/v water to the system. Nevertheless, the formamide test unambiguously differentiated halloysite from kaolinite. N-methylformamide, which yields complexes with a basal spacing of 10.9 Å, could be substituted for formamide (basal spacing = 10.4 Å) for samples containing appreciable amounts of illite-mica.
Cation and Anion Retention by Natural and Synthetic Allophane and Imogolite
Authors: Clark C. J. , McBride M. B. 
Published: August 2006

AbstractThe negative surface charge of synthetic allophanes with a range of Si/Al ratios decreased and positive charge increased with increasing alumina content at a given pH. The phosphate adsorption capacity also increased with increasing Al content. That this relationship between composition and chemical reactivity was not found for the soil allophanes is attributed to the presence of specifically adsorbed organic or inorganic anions on the natural material. Both synthetic and natural imogolites had a much lower capacity to adsorb phosphate than the allophanes and adsorbed anomalously high amounts of Cl− and ClO4− at high pH. It is proposed that intercalation of salt occurs in imogolite, although electron spin resonance studies using spin probes failed to reveal the trapping of small organic molecules in imogolite tubes. These spin probes in the carboxylated form did, however, suggest an electrostatic retention of carboxylate by imogolite and a more specific adsorption by allophane involving ligand exchange of surface hydroxyl. The results illustrate the inherent differences in charge and surface properties of allophane and imogolite despite the common structural unit which the two minerals incorporate.
Thermodynamic Study of Na-K-Ca Exchange Reactions in Vermiculite
Authors: Inoue Atsuyuki 
Published: August 2006

AbstractThe exchange of Na, K, and Ca ions in vermiculite has been studied between 50 and 150°C at a total normality of 0.1. The free energy changes were negative in the Na → K, Ca → K, and Na → Ca exchange reactions, and the cation preference in the vermiculite was Na < Ca < K in the temperature range examined. The enthalpy changes, calculated by application of the van't Hoff equation to the relation between equilibrium constant and temperature, were positive. The cation preference in the vermiculite seems to have been largely controlled by the increase in entropy which was due to the positive values of the entropy change term in the solid for the Na-K and Ca-K exchanges and the positive values of the entropy change in the solution for the Na-Ca exchange. From a thermodynamic analysis of the cation-mixing properties in vermiculite, the observed free energy change in the Na-K exchange was determined solely by the differences of the intrinsic electrostatic binding energy of the cations on the clay surface. That in the Na-Ca exchange was interpreted by taking into account an extra interaction energy of Ca-Ca pairs in addition to the intrinsic energy change. Furthermore, an additional interaction energy between K ions and the clay surface appears to have been added to the free energy change in the Ca-K exchange. In the Na → K and Ca → K exchange reactions a structural modification occurred in the K-equivalent fraction (X̄K) range 0.05–0.6, and a regularly interstratified phase of 15-Å and 10-Å members was formed at 0.05 < X̄K < 0.4.
X-Ray Diffraction Study of Aqueous Montmorillonite Emulsions
Authors: Fukushima Yoshiaki 
Published: August 2006

AbstractAn X-ray diffraction study of aqueous emulsions of a Na-montmorillonite shows that: (1) At low water content, the d-spacings of the montmorillonite increased stepwise with increasing water content; (2) At high water content, sharp (001) peaks due to regular stacking of montmorillonite layers were not detectable, but broad, halo patterns were observed in the low-angle scattering region; and (3) The addition of Ca2+ or H+ to the aqueous emulsions caused Ca-montmorillonite or H-montmorillonite crystals to form. A zig-zag column model of montmorillonite layers fits the observed data for aqueous emulsions of Na-montmorillonite.
Effect of Manganese on the Transformation of Ferrihydrite into Goethite and Jacobsite in Alkaline Media
Authors: Cornell R. M. , Giovanoli R. 
Published: August 2006

AbstractIn the presence of Mn(II), ferrihydrite transforms into Mn-goethite and/or jacobsite. Chemical analysis showed that as much as 15 mole % Mn replaced Fe in the goethite structure. If Mn(III) replaced Mn(II), the formation of jacobsite was suppressed; ferrihydrite transformed into Mn-goethite, and, at high Mn(III) concentrations, a 7-Å phyllomanganate. Low levels of Mn(II) retarded the transformation of ferrihydrite only slightly, whereas in an Mn(III) system the nucleation and growth of Mn-goethite were both hindered. Mn-goethite nucleated in solution, whereas jacobsite appeared to form by interaction of dissolved Mn(II) species with ferrihydrite. Mn suppressed the formation of hematite in these systems; however, Mn-hematite containing as much as 5 mole % Mn was induced to form at pH 8 by adding oxalate to the system. Transmission electron micrographs showed that goethite crystals grown in the presence of Mn were long (≤2 μm) and thin and commonly contained etch pits. The presence of Mn appears to have promoted twinning.
Further Consideration of the 29Si Nuclear Magnetic Resonance Spectrum of Kaolinite
Authors: Thompson J. G. , Barron P. F. 
Published: August 2006

AbstractThe introduction of artificial ±b/3 stacking faults into well-crystallized kaolinite by intercalating and removing hydrazine had no observable effect on the solid-state 29Si nuclear magnetic resonance spectrum of kaolinite. Also, the introduction of such stacking faults did not alter the hydroxyl-stretching region of the infrared spectrum, implying no change in the hydrogen bonding between the displaced layers. Calculations of Si...H distances and Si-O...H angles from reported structures for kaolinite indicated that the resolution of the two Si chemical environments was due to differences in hydrogen-bonding at the surface of the silicate sheet.
Charge Density and Na-K-Ca Exchange on Smectites
Authors: Shainberg I. , Alperovitch N. I. , Keren R. 
Published: August 2006

AbstractCa-K.-, Na-K-, and Ca-Na-exchange isotherms on four reference smectites were studied. The electric charge on the four smectites was due predominantly to cationic substitution in the octahedral layer and varied between 90 and 122 meq/g (cmole(+)/kg) clay. The affinity of the clays for K increased with a decrease in the fraction of K in the exchange phase. The selectivity coefficients of the smectites for K increased with an increase in charge density. The effect was similar in the Na-K- and Ca-K-exchange isotherms. Charge densities on the smectites had no effect on the Ca-Na-exchange isotherm. The electrostatic attraction forces between the platelets increased with increase in charge density. The low hydration energy of adsorbed K was apparently not enough to overcome these attraction forces as the charge density on the smectites increased. Equilibrium between the low hydration energy of adsorbed K and the electrostatic attraction energies between the platelets is postulated to explain the results.
Refinement of the Crystal Structure of A Monoclinic Ferroan Clinochlore
Authors: Rule Audrey C. , Bailey S. W. 
Published: August 2006

AbstractA monoclinic IIb-2 clinochlore from Washington, D.C., contrary to previous studies, is primarily a ferroan rather than a ferrian chlorite. Disorder of tetrahedral Si,Al cations is indicated because of unsuccessful structural refinements in subgroup symmetries. The true space group is C2/m. Slight ordering of Mg, Fe2+, and Fe3+ over octahedra M(l) and M(2) within the 2:1 layer (mean M-O,OH = 2.092 and 2.084 Å, respectively), complete ordering of trivalent Al into the centrosymmetric octahedron M(4) of the interlayer sheet (M-OH = 1.929 Å), and ordering of primarily divalent cations (Mg and Fe) into the two interlayer M(3) octahedra (M-OH = 2.117 Å) exist. The excess of negative charge above unity due to tetrahedral substitution of Al for Si (1.378 atoms) is compensated entirely within the octahedral sheet of the 2:1 layer.Ordering of a trivalent cation into one octahedron in the interlayer should be universal for all stable trioctahedral chlorites. In this specimen the ordering is due to (1) minimization of cation-cation repulsion by layer offsets which provide more space around the trivalent element, and (2) energy minimization by localization of the source of positive charge on the interlayer sheet in one octahedron rather than two. In other structures or for different compositions additional factors can be important also. Most chlorites of the IIb and Ib (β = 90°) types are expected to show disorder of the tetrahedral cations. The b positioning of interlayer and layer provides no preferential driving force for concentration of Si and A1 in any tetrahedron as a consequence of the expected ordering of the interlayer cations. The monoclinic IIb-2 polytype is less abundant in nature than the triclinic IIb-4 and IIb-6 structures, because only half as many possible superpositions of layers exist that will produce monoclinic symmetry. Crystallization factors must also be important, because the IIb-2 chlorite is much less abundant than predicted by this purely geometrical argument.
Reassessment of the Volkonskoite-Chromian Smectite Nomenclature Problem
Authors: Foord Eugene E. , Starkey Harry C. , Taggart Joseph E. , Shawe Daniel R. 
Published: August 2006

AbstractThe name volkonskoite was first used in 1830 to describe a bright blue-green, chromiumbearing clay material from the Okhansk region, west of the Ural Mountains, U.S.S.R. Since that time, the name has been applied to numerous members of the smectite group of clay minerals, although the reported chromium content has ranged from 1% to about 30% Cr2O3. The name has also been applied to some chromian chlorites. Because volkonskoite has been used for materials that differ not only in their chromium content but also in their basic structure, the species status of the mineral has been unclear.To resolve this uncertainty, two specimens of volkonskoite from (1) Mount Efimiatsk, the type locality in the Soviet Union (USNM 16308) and (2) the Okhansk region in the Perm Basin, U.S.S.R. (USNM R4820), were examined by several mineralogical techniques. Neotype sample 16308 has the following structural formula:
(Ca0.11Mg0.11Fe2+ 0.03K0.02)(Cr1.18Mg0.78Fe3+ 0.29Ca0.02)(Si3.50Al0.51)O10(OH)2⋅3.64H2O.Sample R4820 has the following structural formula:
(Ca0.25Mg0.05Fe2+ 0.01K0.03Mn0.01)(Cr1.07Mg0.75Fe3+ 0.35(Si3.59Al0.43)O10(OH)2⋅4.22H2O.Mössbauer spectroscopy indicates that 91% and 98% of the iron is present as Fe3+ in samples 16308 and R4820, respectively. X-ray powder diffraction patterns of both samples have broad lines corresponding to minerals of the smectite group.On the basis of these data, volkonskoite appears to be a dioctahedral member of the smectite group that contains chromium as the dominant cation in the octahedral layer. Smectites containing less than this amount of octahedral chromium should not be called volkonskoite, but should be named by chemical element adjectives, e.g., chromian montmorillonite, chromian nontronite.
Iron Substitution in Montmorillonite, Illite, and Glauconite by 57Fe Mössbauer Spectroscopy
Authors: Johnston J. H. , Cardile C. M. 
Published: August 2006

AbstractThe 57Fe Mössbauer spectra of an iron-rich montmorillonite, an illite, and two glauconites were measured and computer-fitted with appropriate Fe3+ and Fe2+ doublet resonances. The broad experimental Fe3+ resonance of montmorillonite probably arises from Fe3+ in the octahedral sites and a trans-arrangement of OH groups; however, a large variation in the neighboring environment of these sites exists. In illite this Fe3+ resonance is similar but shows less broadening; it arises from Fe3+ located predominantly in trans-OH octahedral sites, with some Fe3+ being located in cis-OH octahedral sites. Because of the increased iron content less variation exists, compared with montmorillonite, in the neighboring octahedral sites. The Fe3+ resonance is narrower still for the glauconites and represents Fe3+ substituting primarily into cis-OH octahedral sites, similar to that previously reported for nontronite.The tetrahedral Fe3+ content is very low for montmorillonite and increases progressively for illite and glauconite, suggesting that a higher tetrahedral Fe3+ content directs Fe3+ in the octahedral layer into cis-OH sites. In montmorillonite, the Fe2+ is located only in trans-OH sites; in illite Fe2+ is largely in trans-OH sites and only slightly in cis-OH sites; and in glauconite, Fe2+ is located largely in cis-OH sites and only slightly in trans-OH sites. These assignments suggest that for Fe2-, the doublet with the larger quadrupole interaction arises from Fe2+ in trans-OH sites and the doublet with the smaller quadrupole interaction, from Fe2+ in cis-OH sites.
Effect of Saturating Cation, pH, and Aluminum and Iron Oxide on the Flocculation of Kaolinite and Montmorillonite
Authors: Goldberg Sabine , Glaubig Robert A. 
Published: August 2006

AbstractThe effect of pH on the flocculation-dispersion behavior of noncrystalline aluminum and iron oxides, kaolinite, montmorillonite, and various mixtures of these materials was investigated. The clays were Na- or Ca-saturated and freeze-dried before use. Critical coagulation concentrations (CCC) of all materials and mixtures were found to be pH dependent. The Al oxide was flocculated at pH >9.5 and the iron oxide was flocculated between pH 6.0 and 8.2; i.e., flocculation occurred at pHs near the point of zero charge (PZC). The CCC of both the Na- and Ca-clay systems increased with increasing pH. The effect of pH was greater for the Na-kaolinite (flocculated at pH 5.8 and having a CCC of 55 meq/liter at pH 9.1) than the Na-montmorillonite system (having a CCC of 14 meq/liter at pH 6.4 and a CCC of 28 meq/liter at pH 9.4). A 50/50 mixture of Na-kaolinite and Na-montmorillonite behaved more like montmorillonite (having CCCs of 13 and 33 meq/liter at pH 6.2 and pH 9.0, respectively). The presence of either noncrystalline oxide decreased the CCC over that of the clay(s) alone; the decrease occurred at pHs >7 for Al oxide and at pHs >6.5 for Fe oxide. Aluminum oxide produced a greater decrease in CCC than Fe oxide, especially at pHs >8. The effect of each oxide on CCC was greatest near the PZC, 9.5 and 7.2 for Al and Fe oxide, respectively.
Transformation of Birnessite to Buserite, Todorokite, and Manganite under Mild Hydrothermal Treatment
Authors: Golden D. C. , Chen C. C. , Dixon J. B. 
Published: August 2006

AbstractInvestigations were conducted to determine the hydrothermal transformations of synthetic birnessite exchanged with different metal ions. Autoclaving in a Teflon-lined stainless steel pressure vessel at 155°C for 24 hr of Mg-, Ca-, La-, and Co-saturated birnessite yielded manganese minerals having 10-Å X-ray powder diffraction (XRD) spacings. The autoclaved Mg-birnessite yielded a mineral identical to natural todorokite in its infrared (IR) spectrum and XRD patterns. High-resolution transmission electron microscopy (HRTEM) provided images having 10-, 12.5-, 15-, and 20-Å wide fringes indicating heterogeneous channel widths in the crystallographic a direction, and IR spectroscopy produced bands at 757, 635, 552, 515, 460, and 435 cm-1, confirming the product obtained by autoclaving Mg-birnessite to be todorokite. Prolonged autoclaving of Mg-birnessite yielded manganite (γ-MnOOH) as a by-product; manganite did not form when the autoclaving time was shortened to 8 hr. Also, when Ca-saturated samples were autoclaved, the product gave d-values of 10 Å, but the XRD lines were broad and heterogeneity of the channel sizes was evident from HRTEM observations. The Ca-derivative had an IR spectrum similar to that of natural todorokite. Images showing 10-Å lattice fringes were observed by HRTEM for the Ni-saturated sample, which also produced an XRD pattern similar to that of the Mg-saturated sample. Co- and Lasaturated samples did not form todorokite, although HRTEM of La-saturated samples indicated some 10-Å lattice fringes that were unstable in the electron beam. Birnessite saturated with Na, K, NH4, Cs, Ba, or Mn(II) gave products having 7-Å spacings upon autoclaving.
Kaolinite, Opal-CT, and Clinoptilolite in Altered Tuffs Interbedded with Lignite in the Jackson Group, Texas
Authors: Senkayi A. L. , Ming D. W. , Dixon J. B. , Hossner L. R. 
Published: August 2006

AbstractThe mineralogy of partially kaolinized strata interbedded with lignite at the San Miguel mine, Atascosa County, Texas, was investigated by X-ray powder diffraction and optical and scanning electron microscopy. The San Miguel lignite occurs in the lower Jackson Group (late Eocene) of southern Texas. Based on mineralogical and micromorphological data, some of these clay partings are probably volcanic in origin and were exposed to variable degrees of in situ kaolinization in a swamp environment. Coexistence of kaolinite, clinoptilolite, and opal-CT in several of these strata suggests that the partially kaolinized volcanic layers were subjected to a subsequent resilication process following burial. Kaolinite is the dominant mineral in the oldest and most kaolinized volcanic layer (underclay) below the lowest lignite bed (seam D). The kaolinite exhibits a well-developed vermicular morphology. The youngest volcanic layer, which occurs stratigraphically above the uppermost lignite seam, is characterized by pseudomorphs of volcanic glass shards and consists mainly of clinoptilolite. Movement of siliceous ground water from this layer to the underlying strata apparently provided silica-rich solutions from which opal-CT and large (as long as 300 μm) euhedral crystals of clinoptilolite precipitated in the fossilized plant roots, veinlets, and fractures within the underlying strata. Micromorphological relationships between the Sirich (opal-CT and clinoptilolite) and sulfide (marcasite and pyrite) minerals in the fossil roots and fractures suggest that the marcasite formed before and pyrite after the resilication process.
Properties of Iron Oxides in Two Finnish Lakes in Relation to the Environment of Their Formation
Authors: Schwertmann U. , Carlson L. , Murad E. 
Published: August 2006

AbstractFifteen iron oxide accumulations from the bottoms of two Finnish lakes (“lake ores”) were found to contain as much as 50% Fe. Differential X-ray powder diffraction and selective dissolution by oxalate showed that the samples consisted of poorly crystallized goethite and ferrihydrite. The crust ores of one lake had higher ferrihydrite to goethite ratios than the nodular ores of the other lake. The higher ferrihydrite proportion was attributed to a higher rate of Fe2+ supply from the ground water and/or a higher rate of oxidation as a function of water depth and bottom-sediment permeability.Values of Al-for-Fe substitution of the goethites determined from unit-cell dimensions agreed with those obtained from chemical extraction if the unit-cell volume rather than the c dimension was used. In very small goethite crystals a slight expansion of the a unit-cell dimension is probaby compensated by a corresponding contraction of the c dimension, so that a contraction of the c dimension need not necessarily be caused by Al substitution.The goethites of the two lakes differed significantly in their Al-for-Fe substitutions and hence in their unit-cell sizes, OH-bending characteristics, dehydroxylation temperatures, dissolution kinetics, and Möss-bauer parameters. The difference in Al substitution (0 vs. 7 mole %) is attributed to the Al-supplying power of the bottom sediments: the silty-clayey sediments in one lake appear to have supplied Al during goethite formation, whereas the gravelly-sandy sediments in the other lake did not. The compositions of the goethites thus reflect their environments of formation.
Compositional and Structural Variations in the Size Fractions of a Sedimentary and a Hydrothermal Kaolin
Authors: Lombardi Gianni , Russell James D. , Keller Walter D. 
Published: August 2006

AbstractThe 16-8-, 8-5-, 5-2-, 2-1-, 1-0.5-, 0.5-0.3-, 0.3-0.1-, and <0.1-μm size fractions were centrifuged from a Georgia (U.S.A.) sedimentary kaolin and a hydrothermal kaolin from the Sasso mine (Italy) and analyzed by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), infrared spectroscopy (IR), differential thermal analysis (DTA) and thermogravimetry (TGA) together with the corresponding whole rocks. All size fractions of the Georgia sample consisted dominantly of well-crystallized, fine-grained kaolinite, associated with minor quantities of smectite. Some halloysite-like elongate particles were noted by SEM in the intermediate size fractions, minor amounts of quartz were identified in the coarsest size fractions, and < 1% noncrystalline material and traces of organic material were suspected in the finest size fraction. The crystallinity of the kaolinite as measured by XRD and IR varied moderately with size. IR suggested that nacrite-like stacking disorder increased with decreasing size for particles < 5 μm in size.In the Sasso sample kaolinite dominated all size fractions and was accompanied by dickite in the coarse and by halloysite in the fine size fractions. Regular mixed-layer illite/smectite (I/S) was present in all size fractions and dominated in the finest. Abundant quartz and traces of alunite were identified in the whole rock and coarsest size fractions. The kaolinite in this sample showed marked variation in stacking order and crystallinity, as shown by changes in XRD, IR, and DTA patterns.The observed compositional and structural variations in the size fractions of the Georgia sedimentary kaolin are small, as expected from formational environment, which was characterized by low temperatures and relative stable genetic conditions. The much more marked differences in composition within the size fractions of the Sasso hydrothermal kaolin are likely a result of the broad range of temperatures and fluid chemistry of its formational environment. The sequence dickite-well-crystallized kaolinite-kaolinite-halloysite is probably temperature-dependent.