FTIR studies of six partially-deuterated montmorillonites (MS) reveal the presence of two O-D stretching bands, one between 2702–2728 cm-1 and another near 2680 cm-1. For homoionic (Li, Na, Mg, Ca, or La) Wyoming-type MS, the position of the higher frequency band, designated as (O-D)h, is between 2714–2728 cm-1, whereas for homoionic Cheto-type MS it is between 2702–2706 cm-1. The lower frequency band, designated as (O-D)1, is in the narrow range of 2674–2684 cm-1. Resolution of two corresponding O-H bands, appearing near 3670 and 3635 cm-1, was observed only after partial dehydroxylation of the smectites. The changes in the relative intensities of the two O-D stretching bands as a function of the smectite type and of the Lewis acidity (charge density) of the exchangeable ion were determined. For Wyoming-type MS, the intensity of the (O-D)h band is much lower than that of the (O-D)l band, whereas for Cheto-type MS, the intensity of the (O-D)h band is about equal or slightly higher than that of the (O-D)l band. The observed resolution can be ascribed tentatively to the presence of (at least) two types of octahedral OH groups in the smectites, the (O-D)h band being assigned to AlMgOH and the (O-D)1 band to AlAlOH groups. Pillaring of Cheto-type MS with hydroxy-Al13 oligocations resulted in products showing much higher thermal stability between 400–600°C compared to that of identically pillared Wyoming-type MS. Compositional and other factors, e.g., CEC values and mode of pillaring, may cause this difference in stability.

Hydrotalcite (HT) interlayered with hexacyanoferrate(II) ions ([Mg4.62Al1.52(OH)12][(Fe(CN)6)0.30-(CO3)0.29]) has been synthesized from the carbonate-HT ([Mg4.52Al1.50(OH)12][(CO3)0.77]) through double ion exchange reactions, and the products have been studied by chemical and physical methods. Mössbauer spectroscopy shows that hexacyanoferrate(II) is held rigidly in the interlayer by electrostatic forces and is characterized by a singlet at 0.01 mm s−1 at 80 K. X-ray diffraction shows an increase of the basal spacing (d003 from 0.78 to 1.1 nm following exchange. Hexacyanoferrate(II) in the interlayer was oxidized to hexacyanoferrate(III) (up to 20%) by dioxygen on dehydrating the interlayer either by drying at 70°C or by washing with nonaqueous solvents like acetone or ethanol. The CN (ν6) band of hexacyanoferrate(II) and (III) is found at 2036 cm−1 and 2112 cm−1, respectively. The presence of an absorption band at 2080 cm−1, assigned to free cyanide anions in the interlayer, suggests that the hexacyanoferrate(II,III) complexes are not inert in the interlayer, cyanide ligands being substituted with either water or hydroxyls. Oxidation and ligand exchange of the hexacyanoferrate(II) are also indicated by Mössbauer spectroscopy.

Parallel-oriented and exceptionally long (> 10 μm) tubes of halloysite occur in the pallid zone of a deeply-weathered lateritic profile on granite in southwest Australia.

Transmission electron microscopy and selected-area electron diffraction of ultrathin sections showed that kaolinite plates within pseudomorphs of mica crystals had fractured at irregular intervals along the a crystallographic axis to produce laths elongated along the b axis. The laths near the edges of the pseudomorphs were less constrained by the pseudomorph and had rolled to produce halloysite tubes. The tubes varied in diameter and degree of roundness. Some tubes were polyhedral rather than cylindrical in cross section. The length and number of planar faces in a tube and the angle between faces varied, exhibiting no consistent pattern.

Tubes in dispersed clay samples showed two types of twinning. In the first type, tubes and associated laths were joined together side by side. In the second type, single tubes bifurcated into two individual tubes. It is proposed that the first type of twinning occurred by folding of adjacent laths that remained joined together while the second type occurred due to exfoliation of a thick lath followed by folding of the exfoliated lath fragments into tubes.

Analytical electron microscopy showed that the chemical compositions of halloysite tubes, laths, and kaolinite plates were similar with the average cation exchange capacity of single tubes being small (4.5 meq/100 g) but higher than values for laths (2.8 meq/100 g) and plates (1.9 meq/100 g).

Sorption of benzene onto Cu-montmorillonite was characterized by Fourier transform infrared (FTIR) spectroscopy and 13C magic angle spinning nuclear magnetic resonance (MAS NMR). Under anhydrous conditions, chemisorption of benzene in the interlamellar region of Cu-montmorillonite led to the formation of a dark red surface complex that exhibited a vibrational spectrum similar to that of doped poly-p-phenylene. When the benzene sorption reaction was carried out under high relative humidity conditions, polymerization of benzene did not occur. The FTIR spectrum of the surface complex formed under wet conditions exhibited vibrational bands that could not be assigned to those of the parent benzene molecule or to those of previously observed chemisorbed Type I or Type II complexes. 13C MAS NMR spectra of 13C-enriched benzene sorbed onto Cu-montmorillonite powder showed the presence of two groups of peaks that could be assigned to aromatic and aliphatic carbon respectively.

Rectorites containing various amounts of Ca were found at the Sano Mine, Nagano Prefecture, Japan. The Ca content in nonexchangeable form varied from 1.0 to 3.9% CaO. With more than 3.4%, they may be called Ca-rectorite. Chemical data of the most Ca-rich sample showed that Ca was the dominant interlayer cation, and gave a structural formula of (Mg0.16)EX(Ca0.59Na0.27K0.17)FIX[Al3.94Mg0.08 Fe0.07Ti0.01](Si5.85Al2.15)O20(OH)4. This sample is apparently the most Ca-rich rectorite reported to date. The Greene-Kelly test and an intercalation examination by octadecylammonium indicated that the expandable component layers were beidellitic. Assuming the tetrahedral composition of the expandable component layers are similar to the average tetrahedral composition of beidellite of (Si3.6Al0.4), the tetrahedral composition of the mica-like component layers was calculated to be (Si2.25Al1.75). This was closer to a brittle mica (margarite) than to a true mica. Examination of chemical data for several Ca-rectorite samples from different localities, including those from the Sano Mine, showed a trend of increasing Ca content as Al increased and Si decreased. Ca-rectorite exhibited characteristic infrared absorption bands at 480, 670–700 and 900–930 cm−1, which became more intense as Ca content increased. These bands also corresponded to major absorption bands of margarite.

The cause of pH and ionic strength-dependent proton and hydroxyl adsorption onto kaolinite is specific binding at edge Al and Si sites, and it can be modeled as a function of temperature with a triple layer model (TLM) of the mineral-solution interface. Exchange of Al for protons and hydroxyls is observed at low pH, with a stoichiometry approaching 1:3 (Al:H+). Adsorption of organic acids from dilute solutions depends on: 1) solution pH; 2) the functionality of the acid; and, to a lesser extent, 3) temperature. Such adsorption may occur primarily at Al sites exposed on kaolinite edges, as indicated by sorption experiments on the constituent oxides, where negligible sorption was observed on SiO2 (quartz), but was significant on Al2O3 (corundum) surfaces. Under similar conditions, oxalate adsorbs more strongly than acetate or formate to aluminol sites.

Cetyltrimethylammonium- and tetradecyltrimethylammonium-intercalated magadiites were prepared by direct syntheses, starting from sodium metasilicate (Na2O/SiO2 = 1.0) and nitric acid. Total substitution of sodium by cetyltrimethylammonium or tetradecyltrimethylammonium cations was not achieved in the range of surfactant: silicon molar ratios used in this study. When a phosphoniun-based surfactant replaces the ammonium surfactants in the same procedure, the result of the synthesis is a mixture of quartz and unmodified surfactant. If dodecylammonium bromide is used, an MCM-41 molecular sieve is obtained. The substitution of the silicon source by tetramethylammonium silicate or of nitric acid by hydrochloric, hydrofluoric, or acetic acids also yields MCM-41 molecular sieves, indicating that the formation of magadiite is greatly dependent on the presence of sodium cations and nitrate anions.

We applied the hard and soft acid-base (HSAB) model (Xu and Harsh 1990a, 1990b) to bivalent cation exchange on a purified Ca-montmorillonite. As a result, a satisfactory model is proposed to describe the gradual selectivity of exchange with Ca for 4 of the 6 metals studied (Cd, Cu, Pb, Zn). The selectivity is predicted as a function of the differences of electronegativity and softness of the metals. The deviation of Ni and Co data from the predicting model is interpreted in terms of hydration (Ni and Co being the most strongly hydrated ions). The fitting parameters of the model, α and β, are related to the electronegativity and softness characteristics of the surface, respectively. Their ratio gives information on the nature of bonding. Results suggest that covalent bonding modifies electrostatic interactions, which in turn affect selectivity, with an increasing influence of covalent bondings in the order: Pb < Cd < Zn < Cu.

To balance the lack of representativity of the model for the small molar fraction (NM), we propose to associate to the HSAB model an equation describing the variation of the Vanselow selectivity coefficient as a function of the molar fraction of metal on clay.

This study examines the evolution of the texture, structure, and chemical composition of rocks derived from clastic materials of the Ossa-Morena Zone (Hesperian Massif, Spain). Previous studies of phyllosilicates in these rocks (by X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray analysis, and electron microprobe) indicated a temperature decrease from bottom (epizone conditions) to top (diagenetic conditions) of the rock section.

At the nanometer scale, phyllosilicate packets form large angles where grains intersect with no preferred orientation. With metamorphic grade, packets are wide and defect free, compared to packets at lower grade. These packets are ∼ 15 layers under diagenetic conditions to >80 layers in the epizone. Dioctahedral K-rich micas (muscovite, phengite, and illite) have coexisting 1Md, 1M, and 2M polytypes. Long-period polytypes of 4, 5, and 6 layers are reported for the first time in dioctahedral K-rich micas. The chemical compositions of the micas are nearly identical in the anchizone and the diagenetic zone, comprising an illitic (0.8 atoms per formula unit, a.f.u., of K) and a phengitic component (0.15 a.f.u, of Mg and 0.13 a.f.u, of Fe). Fe may correspond to a ferrimuscovitic substitution. Epizone samples have a high phengitic content (Mg = 0.24 a.f.u.) and almost no illite component. One diagenetic sample has coexisting berthierine, trioctahedral chlorite, sudoite, and corrensite. Berthierine and chlorite are identical in composition. Because of the clastic nature of the system, the composition of corrensite is not typical of other corrensites, with higher Al content, Fe/Mg ratio at ∼1, and K as the exchangeable cation.

Textural differences between the diagenetic zone and the anchizone are the progressive increase in the size of dioctahedral K-rich mica grains, which involves an increasing illite crystallinity based on the Kübler index. The chemical compositions of these micas are illite (diagenesis and anchizone) and phengite in the epizone. There are no intermediate phases, suggesting a compositional gap between illite and phengite. The coexistence of different polytypes of dioctahedral K-rich micas and the absence of chemical homogeneity indicate disequilibrium in the Cambrian pelitic rocks studied.

Formation of authigenic trioctahedral Mg-rich smectite is common in evaporative lake sediments, but was not described previously in modern marine evaporative environments. This study documents formation of authigenic K-rich, Mg-smectite during very early diagenesis in the dominantly siliciclastic Salina Ometepec (Baja California), a large supratidal evaporative sabkha complex near the mouth of the Colorado River. Here, sediment pore waters are exceptionally Mg2+-rich relative to other marine evaporative environments due to suppressed sulfate reduction which limits production of carbonate alkalinity and, hence, carbonate (particularly dolomite) precipitation. Sediment cores were obtained along a five km transect seaward across the hypersaline mud flat to evaluate how these atypical geochemical conditions would affect the clay mineral compositions.

Scanning transmission electron microscopy (STEM) observations show that the smectite from the marine Inlet, near the sediment source, consists of grains of irregular shape that give selected area diffraction (SAED) patterns reflecting dominant turbostratic stacking. Analytical electron microscopy (AEM) analyses indicate that K+ is the dominant interlayer cation; the mean composition is approximately K0.7(Al3.3Fe(III)0.3Mg0.5)(Al0.5Si7.5)O20(OH)4. Such smectite is implied to be detrital in part because it is similar to smectite known to be deposited by the Colorado River.

Smectite from the hypersaline mud flat occurs as aggregates of small subhedral pseudohexagonal plate or lath-shaped crystals ≤250 nm in diameter, with thicknesses varying between three and ten layers. The SAED patterns reflect substantial turbostratic stacking, but with a greater frequency of interlayer coherency as compared with detrital smectite. Crystals from greater sediment depths are larger and more nearly euhedral. This smectite is dominantly trioctahedral, with mean composition approximately K0.7(Al0.7Fe(III)0.5Mg4.45)(Al1.2Si6.8)O20(OH)4 (saponitic). This smectite is inferred to be dominantly authigenic in origin.

The X-ray diffraction (XRD) and STEM/AEM data collectively imply that detrital aluminous dioctahedral smectite reacts to form authigenic Mg-rich trioctahedral smectite, driven in part by the high Mg2+/ Ca2+ ratio of pore waters. Such early-formed Mg-rich smectite may be the precursor for the trioctahedral mixed-layer smectite, corrensite, and chlorite assemblages found in ancient marine evaporative sequences. These results also add to the accumulating evidence that interlayer K+ in marine smectite is fixed during the earliest stages of marine diagenesis near the sediment water interface.

Seven Al-containing lepidocrocite samples, γ-Fe1−xAlxOOH, prepared from FeCl2/Al(N03)3 solutions with initial Al/(Al + Fe) mole ratios Ci of 0.0025, 0.01, 0.025, 0.05, 0.075, 0.10 and 0.15 mol/mol, were examined by means of Mössbauer spectroscopy at room temperature (RT) and at various temperatures in the range of 8 to 80 K. The spectra at RT and 80°K consist of broadened quadrupole doublets and were analyzed in terms of a single doublet and of a model-independent quadrupole-splitting distribution, the latter yielding the best fit. The observed variations of the quadrupole-splitting parameters with increasing Ci are inconclusive as to whether the Al cations are substituting into the structure. The temperature at which the onset of magnetic ordering is reflected in the spectra, was measured by the thermoscan method with zero source velocity. A gradual shift from 50 K for Ci = 0.0025 mol/mol to 44 K for Ci = 0.10 mol/mol was observed for that temperature. As compared to earlier studies of Al-free γ-FeOOH samples with similar morphological characteristics, the fractional doublet area in the mixed sextet-doublet spectra at 35 K is significantly higher for the present lepidocrocites. This observation is ascribed to the substitution of Al cations into the lepidocrocite structure. A similar conclusion is inferred from the variation with Ci of the maximum-probability hyperfine field derived from the spectra recorded at 8 K and fitted with a model-independent hyperfine-field distribution. The magnetic results suggest that for the sample corresponding to Ci = 0.15 mol/mol, not all of the initially present Al has been incorporated into the structure.

Rehydration is shown to be straightforward for the reconstruction of polyoxometallate-pillared layered double hydroxides. Zn-Al hydrotalcite-like minerals were prepared with Zn/Al ratios of 1 to 5 by coprecipitation at pH 7. Good crystallinity was obtained for samples with Zn/Al ratios above 2. Thermal decomposition was achieved by calcining the samples at 300 to 900 °C. The calcined samples were exposed to decarbonated water, with or without hydrothermal treatment to evaluate reconstruction of the hydrotalcite-like minerals by rehydration. Restoration of the hydrotalcite-like structure was found to be independent of the Zn/Al ratios for samples calcined between 300 and 400 °C; however, asecond phase, aluminum hydroxide or zinc oxide, was generally detected. A spinel phase, formed during the calcination of samples at temperatures above 600 °C, inhibited reconstruction of the hydrotalcite-like phase. The rehydrated hydrotalcite-like minerals had Zn/Al ratios close to 2, irrespective of the chemistry of the starting material.

Two orientations of white micas with subordinate chlorite have been observed in a fine-grained (50 Å to 2 μm) matrix of a Silurian lower anchizonal mudrock from central Wales: one parallel to bedding and one parallel to cleavage that is approximately 30°-50° to bedding. Bedding-parallel micas consist of small (50-200 Å thick) deformed packets (1Md polytype) and larger (100 Å-2 μm) strain-free grains (2M1 polytype). All strained micas and some strain-free grains have compositions varying from Mu86Pg14 to Mu58Pg42, intermediate to muscovite and paragonite, and falling within the Mu-Pg solvus. Individual packets of layers are chemically homogeneous and some of them give only one set of 00l reflections (d ≈ 19.6 Å). Micas with such intermediate compositions are metastable. Some packets of coarse, strain-free micas have compositions of approximately Mu93Pg7 or Mu11Pg89. Split pairs of 00l reflections with d-values of 20 Å and 19.6 Å, and 20 Å and 19.2 Å, respectively, were observed in some SAED patterns, suggesting coexistence of muscovite and intermediate Na/K mica (∼Mu60Pg40), and of discrete muscovite and paragonite, consistent with the splitting of the basal reflections of micas as observed in bulk-rock XRD patterns. Cleavage-parallel micas (2M1 and 3T polytypes) occur as strain-free large grains (200 Å to 2 μm) of discrete muscovite (Mu100Pg0) and paragonite (Mu6Pg94), often with subhedral to euhedral cross-sections.

The data suggest that bedding-parallel metastable micas with disordered interlayer K and Na were initially derived from alteration of smectite during burial diagenesis. They subsequently underwent dissolution, with crystallization of more evolved bedding-parallel micas during deep burial. Discrete grains of stable muscovite and paragonite then crystallized in the cleavage orientation through tectonic stress-induced dissolution of bedding-parallel matrix micas. Combined XRD and TEM/AEM data further show that the so-called 6:4 ordered mixed-layer paragonite/muscovite actually corresponds to cation-disordered, homogeneous mica of intermediate composition.

Prograde evolution of illite/smectite occurring in an unusually-thick (8000 m) sequence of Mesozoic-Cenozoic sediments in the Basque-Cantabrian Basin, Spain, has been studied using XRD and TEM/AEM. The sediments, which are only slightly tilted, cover the range from smectite to illite, and the most deeply buried ones are unique in that they span the range from diagenesis through low-grade metamorphism (anchizone), with no apparent overprinting due to tectonic deformation.

Pelites are absent from the shallow section, but smectite occurs in marls as high-charge, K-dominant and low-charge, K-poor anastomosing arrays of layers. At intermediate depths, authigenic clay is identified largely as R1 I/S, coexisting with packets of R≫3 I/S (nearly pure illite), where illite-like and smectitelike layers can be identified by contrast in TEM images, which is consistent with XRD data. The authigenic clay of the deepest samples consists of illite with no or almost no expandable layers, which occurred as packets with layers largely subparallel to bedding, K-deficient composition in comparison with muscovite, 1Md-like SAED patterns, and 100 Å mean packet thickness. There is no evidence of deformation stress-induced, non-bedding-parallel clays in the deepest samples. Detrital micas with either a phengiterich or a phengite-poor composition range dominate the phyllosilicate fraction of all the samples. Detrital micas show no changes over the diagenesis/metamorphism range and appear to have behaved as if isolated from authigenic clays.

Authigenic clays occur as bedding-subparallel packets that evolved during passive burial metamorphism through dissolution/crystallization of less-evolved clays. Where illite-like and smectite-like layers can be identified, TEM images imply a discontinuous series in which packets of R1 I/S (50% I) transform to packets of nearly-pure illite, that is, an Ostwald-step-rule-like sequence. Such immature illite remains unmodified with further burial, and is apparently the potential predecessor of stress-induced, highly-evolved mica of higher-grade, tectonically-deformed pelites.

Microbial reduction of clay mineral structural Fe(III) decreases the swelling of nontronite gels, most importantly at intermediate oxidation states (40 to 80 cmol Fe(II) kg−1 clay). The purpose of this study was to establish whether microbial reduction of structural Fe(III) decreased the swelling of other Fe-bearing smectites and to discern the influence that organic compounds of microbial origin (bacterial cells, cell fragments and/or exudates) may have on clay swelling and texture. Structural Fe(III) was reduced by incubating smectite suspensions with either a combination of Pseudomonas bacteria or a mixture of anaerobic bacteria. The influence of organics on clay swelling was estimated on smectites suspended in either organic or inorganic media in the absence of bacteria. The gravimetric water content of the reduced clay gels equilibrated at various applied pressures was recorded as a function of Fe oxidation state. Transmission electron microscopy (TEM) was employed to determine the influence of bacteria and type of media on the texture of reduced smectite gels. Reduction of structural Fe(III) by bacteria decreased the swelling pressure of all Fe-bearing smectites. Increased clay swelling, due to the presence of organics (organic medium, exudates or cell fragments), was correlated to the total Fe content, the extent of structural Fe reduction, as well as the initial swelling characteristics of the Fe-bearing smectites. High structural Fe(II) contents (>50 cmol Fe(II) kg−1) resulted in increased attractive forces between clay platelets that decreased clay swelling, even in organic medium suspensions. Microbial reduction resulted in increased face-face association of individual clay layers, forming larger and more distinct crystallite subunits than in nonreduced clay gels. But, perhaps more importantly, microbial reduction of structural Fe(III) resulted in an increased association between crystallite subunits and, thus, an overall larger particle size and pore size distribution, due to the interaction of bacteria ceils, cell fragments and organic exudates.

A sequence of interstratified illite-smectite (I-S) and illite in Paleozoic pelites and metapelites from the Iberian Range, Spain, was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The fine-grained matrix of diagenetic pelites is composed of I-S with sequences of illite- and smectite-like layers in a given sample. The Reichweite (R) values as determined by XRD and averaged over heterogenous I-S layer sequences increase with increasing grade, apparently continuously, in sharp contrast with TEM observations of other published sequences. Changes in I-S sequences along layers are rarely observed. In the higher-grade diagenetic pelites, I-S coexists with illite. Each I-S phase has a composition similar to that of illite, implying unique Al-Si distributions in contrast to smectite and muscovite. Selected area electron diffraction (SAED) patterns of I-S and illite are diagnostic of 1Md polytypism. Anchizonal metapelites consist of larger packets of well-crystallized muscovite, with SAED patterns corresponding to a two-layer polytype.

The continuous sequence of changes studied by TEM in I-S sequences and lateral transitions among these units is consistent with illitization by layer-by-layer replacement, although other processes are possible also. Replacement of individual layers probably occurs via fluids at reaction interfaces, in contrast to solid-state reactions, sensu strictu. The transition from the diagenetic to anchizonal rocks (transition in textures and formation of muscovite-2M1) occurred via dissolution/crystallization, however, presumably by tectonic stress. XRD and TEM data imply a consistent prograde trend in the sequence, the XRD data denning the average, long-range Reichweite ordering sequence, whereas the TEM data define the short-range layer sequences.

X-ray powder diffraction (XRD), thermal gravimetric analysis (TGA), surface area measurements, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy were used to examine the surface properties of organosilane-modified smectite-type aluminosilicate clays. Organic modified clays derived from the reactions of montmorillonite (containing 93–95% montmorillonite from a bentonite, <1% quartz, and 4–6% opal CT) with octadecyltrichlorosilane (C18H37SiCl3) and octadecyltrimethoxysilane [C18H37Si(OMe)3] are highly hydrophobic. Surface loadings of the modified clays depend on the organosilane and the solvent, and they range from 10 to 25 wt. %. The organic species are probably adsorbed to the outer surfaces and bound to the edges of the clay via condensation with edge-OH groups. Encapsulation of montmorillonite with C18H37SiCl3 and C18H37Si(OMe)3 resulted in a hydrophobic coating that acts like a “cage” around the clay particles to limit diffusion. Basal spacings of the organic modified clays remain at ∼15 Å upon heating to 400°C in N2, whereas those of unmodified clays collapse to ∼10 Å. A considerable reduction in surface area (by 75–90%) for organic modified clays is observed, which is consistent with the existence of a surface coating. The solvent used can affect the amount of organic silane coated on the clay particles, whereas the difference between the products prepared using C18H37SiCl3 and C18H37Si(OMe)3 in the same solvent is relatively small. The carbon and oxygen K-edge NEXAFS spectroscopy of the modified montmorillonite surfaces showed that surface coatings on the outside of the clay particles exist. The encapsulating system may allow for economical remediation and storage of hazardous materials.

We study the Diophantine transference principle over function fields. By adapting the approach of Beresnevich and Velani [‘An inhomogeneous transference principle and Diophantine approximation’, Proc. Lond. Math. Soc. (3) 101 (2010), 821–851] to function fields, we extend many results from homogeneous to inhomogeneous Diophantine approximation. This also yields the inhomogeneous Baker–Sprindžuk conjecture over function fields and upper bounds for the general nonextremal scenario.