X-ray diffraction (XRD) characterization of natural and intercalated smectites is usually limited to the apparent d-value estimated from the peak maxima in the raw data. This can lead to the misinterpretation of the measured data. In the case of XRD, the interference function is modulated by instrumental factors (Lorentz-polarization factor, diffraction geometry) and physical factors (structure factor, surface roughness effect). These effects lead to diffraction profile distortions, depending on the diffraction angle and peak full width at half maximum (FWHM). As a result, the diffraction profiles for structures with large line broadening (FWHM > 1°) exhibit a significant peak shift (Δd ∼ 1.5 Å), especially at low angles (2θ ≤ 10°). The present work deals with the detailed analysis of all these effects, their corrections and their consequences for the interpretation of diffraction patterns (including possible errors in determining lattice parameters or the structure model). The investigated materials were montmorillonites (MMT) intercalated with hydroxy-Al polymers. Diffraction profile analysis revealed the corrected d-values and showed that the intercalated sample is not a mixed-layered structure. As a result a structural model of the interlayer is presented.

The hydroxyl deformation modes of kaolins have been studied by Fourier transform (FT) Raman spectroscopy. Kaolinites showed well-resolved bands at 959, 938 and 915 cm−1 and an additional band at 923 cm−1. For dickites, well-resolved bands were observed at 955, 936.5, 915 and 903 cm−1. Halloysites showed less-resolved Raman bands at 950, 938, 923, 913 and 895 cm−1. The first 3 bands were assigned to the librational modes of the 3 inner-surface hydroxyl groups, and the 915-cm−1 band was assigned to the libration of the inner hydroxyl group. The band in the 905 to 895 cm−1 range was attributed to “free― or non-hydrogen-bonded inner-surface hydroxyl groups. The 915-cm−1 band contributed ~65% of the total spectral profile and was a sharp band with a bandwidth of 11.8 cm−1 for dickite, 14.0 cm−1 for kaolinites and 17.6 cm−1 for halloysites. Such small bandwidths suggest that the rotation of the inner hydroxyl group is severely restricted. For the inner-surface hydroxyl groups, it is proposed that the hydroxyl deformation modes are not coupled and that the 3 inner-surface deformation modes are attributable to the three OH2-4 hydroxyls of the kaolinite structure. For intercalates of kaolinite and halloysite with urea, a new intense band at ~903 cm−1 was observed with concomitant loss in intensity of the bands at 959, 938 and 923 cm−1 bands. This band was assigned to the non-hydrogen-bonded hydroxyl libration of the kaolinite-urea intercalate. Infrared reflectance (IR) spectroscopy confirms these band assignments.

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.

Magnesite pebbles in Miocene lacustrine conglomerates in northwest Turkey have been partially to totally replaced by sepiolite. Only 5% of the magnesite pebbles have been converted to essentially pure sepiolite; the rest represent mixtures of magnesite and sepiolite. This process of sepiolitization is documented by X-ray diffraction (XRD), chemical, scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) techniques. These techniques show that the sepiolitization proceeds from the rim towards the core of the pebbles. The conglomerates, with pebbles of magnesite and ultramafic rocks, were deposited in a near-shore environment on the margin of a large Miocene lake with an ophiolitic substratum. The diagenetic transformation of magnesite to sepiolite is believed to have been caused by the interaction of mixed meteoric and lacustrine waters, which were undersaturated with respect to magnesite. The sepiolitization occurred during the highstands of the lake, when the near-shore conglomerates were flooded by the silica-rich lake waters. The pH of the water during the sepiolitization was probably on the order of 10.5–11.5. The sedimentary magnesite beds in the center of the Miocene basin show no sepiolitization, which is explained by the presence of pore water saturated with respect to magnesite.

The magnesite-sepiolite replacement process is chemically modeled as a 4-stage process from dimerization to polymerization.

The reactivity of basal surfaces, steps and edges of muscovite was studied by imaging surface precipitates of PbCl2 using atomic force microscopy (AFM). We reacted PbCl2 solution with freshly cleaved muscovite surfaces and found that PbCl2 precipitates were formed on the basal surfaces, steps and edges. It was observed that PbCl2 precipitated preferentially along the steps compared to the basal surfaces and that PbCl2 precipitates at multiple-layer edges were needle-shaped and oriented in different directions. One of the muscovite samples we cleaved had muscovite fragments sitting on the freshly cleaved surfaces. These fragments resulted from previously formed cracks. Thus, we were able to compare the reactivity of the weathered surfaces with that of freshly cleaved surfaces. It was found that PbCl2 was not precipitated along the edges of previously cracked muscovite fragments. These results clearly demonstrated that the edges of freshly cleaved muscovite are the most reactive surface sites, whereas the edges of weathered muscovite are not as reactive. We believe that the surface reactivity of the edges of freshly cleaved muscovite is likely due to terminal or Al-OH1/2− groups on these crystalline surfaces, which favor adsorption of Pb2+ ions and the subsequent nucleation and precipitation reactions. We also investigated the effect of drying rate on the morphology of the surface precipitates. Fast drying resulted in a nearly complete covered surface with a leaflike morphology, whereas slow drying resulted in more isolated surface clusters.

The smectite-to-illite diagenetic transformation has been documented in 5 different sedimentary basins using X-ray diffraction (XRD). Intermediate reaction products coexisting because of the effect of kinetics on this reaction have been characterized using decomposition of XRD patterns and comparison with calculated patterns. The nature and relative abundances of the various subpopulations of particles are shown to vary as a function of the geothermal gradient and of the age of the sediment. In all sedimentary basins that experienced a low steady geothermal gradient the physico-chemical characteristics (coherent scattering domain size [CSDS], junction probabilities) of intermediate mixed-layered illite-smectites (I-S) are similar. However, both the relative abundance and the crystallinity of the end-member illite increase as a function of the age of the sediment.

In basins that have experienced a higher geothermal gradient, the CSDS of the I-S subpopulation is higher for a given illite content, indicating a slightly different reaction pathway. This difference in the characteristics (peak position and width) of elementary peaks may be used to infer the presence of such a high geothermal gradient when no other data are conclusive. In this case the growth of the illite end-member is favored over the growth of intermediate I-S phases even in young basins. Illitic phases formed from the alteration of kaolin minerals exhibit characteristics similar to the reaction products of the smectite-to-illite diagenetic transformation in the case of a high geothermal gradient. In contrast with what is observed in shale diagenesis, the characteristics of the illitic subpopulations describe a continuum with absolutely no gap in between subpopulations. In sandstone reservoirs, the various subpopulations crystallize simultaneously from a kaolin precursor. As a consequence, no kinship is expected between the various subpopulations.

Heulandite-group zeolites are abundant in the Miocene pyroclastics from Western Anatolia, Turkey. We investigated the relation between the I(111)/I(3¯11) intensity ratios measured by X-ray diffraction (XRD) and the content of exchangeable cations for 15 samples of natural heulandite-group minerals gathered from the Gördes and Bigadiç regions of Western Anatolia. The intensity ratios range from 0.77 to 0.94 in natural heulandites and from 1.38 to 1.80 in natural clinoptilolites. The data obtained from Na-, K- and Ca-exchanged forms of a heulandite and clinoptilolite show that the intensity ratio increases with Na-, K- and Ca-exchange in heulandite and also with Na- and K-exchange in clinoptilolite, whereas it decreases with Ca-exchange in clinoptilolite. The intensity ratios were calculated using the known structural data of clinoptilolites to understand the effect of positions, amounts and kinds of exchangeable cations and water molecules. An increase in Na and Ca may increase or decrease the intensity ratio, depending on their sites and occupancies. Potassium causes a significant increase in the intensity ratio and an increase in Mg decreases the intensity ratio. There is a strong correlation between the intensity ratio I(111)/I(3¯11) and (Na + K)/(Ca + Mg) ratio and thermal stability, both of which have been used to characterize heulandite-group minerals.

Smectite and fine-grained quartz were separated from 6 volcanic ash samples collected in Japan from Shinmoe-dake Volcano, southern Kyushu, and Mt. Usu Volcano, southern Hokkaido. Oxygen isotope ratios of smectite in the volcanic ash range from +6.9 to +12.9 per mill (‰), which are comparable to the values of smectite (δ18O = +6.5 and +9.4‰) from currently active geothermal fields. Evaluation of the oxygen isotope data from smectite (δ18O = +6.9 and +8.4‰) and quartz (δ18O = +6.6 to +11.2‰) in volcanic ash erupted from Shinmoe-dake in 1959 indicates a hydrothermal origin at elevated temperatures (150 to 270 °C) from waters that have calculated 8180 values (8180 = -3 to +5%o) that are enriched relative to local meteoric water (δ18O = -7 to -8‰). This precludes an authigenic formation of the smectites under ambient temperatures in crater lakes and/or somma-atrios which had been previously proposed as a plausible mechanism. A peculiar clay flow was extruded on the somma-atrio of Mt. Usu Volcano. The isotopic composition of the clay (<0.5 μm, δ18O = + 12.2‰) and evidence from geophysical exploration over volcanic vents of Shinmoe-dake support the concept that extensive hydrothermal alteration is taking place within volcanic vents.

The question of whether clay minerals can be biogenically transformed as a result of lichen activity at the lichen-rock interface remains unresolved. We applied several microscopical and analytical techniques—scanning electron microscopy-back-scattered electron (SEM-BSE), energy dispersive spectroscopy (EDS) and high-resolution transmission electron microscopy (HRTEM)—in an attempt to address this issue. Unaffected granitic biotite and bioweathered material from the granitic biotite and Parmelia conspersa lichen thalli interface were examined using HRTEM after ultrathin sectioning. The n-alkylammonium treatment of ultrathin sections was carried out in order to study the biogenous mineralogical transformation of the biotite. Microsamples proceeding from unaffected biotite zones demonstrated homogenous 10-Å d(001)-value biotite phase. HRTEM images of lattice fringes of samples taken from the lichen-biotite contact zone reveal large areas of both unexpanded (10-A) and randomly and R = 3 distributed expanded (from 14- to 30-Å) layers of phyllosilicates identified as interstratified biotite-vermiculite. Results of artificial biotite weathering (replacement of K by Ca ion) also revealed the biotite-vermiculite phase formation, indicating that K release in biotite is one of the mechanisms responsible for interstratified mineral phase formation. Two parallel processes, physical exfoliation of biotite and inter-layer ionic exchange of K and subsequent vermiculite formation, are the mechanisms for biotite bioweathering induced by lichens.

Diffusion of alkali and low-atomic-number elements during the microbeam analysis of some silicates by analytical electron microscopy (AEM) has been known for some time. Our repeated analyses at 300 kV of kaolinite, halloysite, smectite, biotite, muscovite and pyrophyllite, however, showed differential loss (relative to Si) of not only alkali elements (such as K, Na, Mg) and low-atomic-number elements (such as Al) but also higher-atomic-number elements (such as Fe, Ti). For AEM of these phyllosilicates, a Philips EM430/EDAX facility with a tungsten filament was used to provide a current of 0.3 nA in a stationary beam of nominal diameter 90 nm. The loss of Al in kaolin minerals during analysis is particularly severe. Kaolin crystals can be damaged by the electron irradiation over several seconds, making it the most sensitive clay to the electron beam; in general, relative phyllosilicate stabilities are kaolin < smectite < pyrophyllite < mica. A clear dependence of element loss on crystallographic orientation has been observed for layer silicates in our study; a greater element loss occurred when the plane of the specimen foil was perpendicular to the basal planes of the phyllosilicate crystals than when the foil was parallel to the basal planes. Lower beam current, larger beam diameter and thicker specimens all reduce the loss of elements. The initial stage of irradiation produces highest rates of element loss and the rate of loss can be fitted by an exponential decay law. The analyses at low temperature of phyllosilicates showed that element loss remains serious in our analytical conditions. Since the element loss appears to be instrument- and method-dependent, one should use closely related, well-characterized phyllosilicates as compositional standards to calibrate any AEM instrument that is to be used to analyze unknown phyllosilicates, and the standards and unknowns should be analyzed under identical conditions.

The rapid phase quantification method using X-ray diffraction (XRD) with a position-sensitive detector (PSD), outlined by Cressey and Schofield (1996), has been extended to facilitate mineral phase quantification of clay-bearing samples. In addition, correction factors for differences in matrix absorption effects have been calculated and applied. The method now enables mudrock mineralogy to be quantified rapidly and efficiently. Using this approach overcomes many of the problems hitherto associated with the quantitative analysis of clay minerals, in particular the effects of preferred orientation of crystallites and variable sample-area irradiation, that make the task of quantification extremely difficult by conventional Bragg-Brentano scanning diffractometry.

Interaction between n-butylammonium (BA) chloride and vermiculite from Santa Olalla (Spain) has been studied in large flake (5 × 5 × 0.1 mm) or ground powder (≤80 µm) samples. The differences in adsorption and decomposition of BA ions in both particle sizes have been established. In the interlamellar space, the BA ion remains unaltered in powder samples, but is degraded in flakes. The experimental results suggest decomposition of the BA in the interlamellar space of vermiculite flakes by breaking of the C-N bond. The degradation of BA takes place over a short period. The variety with BA in the interlamellar space is transformed into a new one, due to the degradation of alkylammonium. The transformation occurs through an interstratified phase formed between BA-vermiculite and NH4-vermiculite, and finally a phase appears in which only ammonium is present in the interlamellar space. Due to the many industrial applications of alkylammonium-clays, determination of the stability of alkylammonium in the interlamellar space of clay minerals is of great importance.

The boundary between diagenesis and metamorphism most likely involves the change of illite into mica. Observations of this change can be made using decomposed X-ray diffraction (XRD) spectra of illitic clay mineral assemblages in pelitic sedimentary rocks.

XRD analysis of the (003) diffraction peak of diagenetic illites indicates that there are 2 components, one of small coherent diffraction domains and another of larger domain size. Peak width, shape and position define these fractions. The smaller domain size material in diagenetic rocks is highly illitic (>95%) but contains some smectite layers and can be best described by Gaussian shapes. The grains with larger diffracting domains show no expanding layers.

Metamorphic illites (probably muscovites) show no smectite interlayers in any fraction. In the transition from sedimentary and diagenetic to metamorphic illites, new grains of smectite-free illite are formed at the expense of the older minerals. This suggests that the new metamorphic minerals are recrystallized phases. Metamorphism of illites then produces new mica phases.

Hydroxyaluminosilicate (HAS) and hydroxyaluminum (HyA) ionic solutions having final Al concentrations ranging from 3.74 to 4.00 mM; NaOH/Al molar ratios of 1.0, 2.0 and 2.5; and Si/Al molar ratios of 0.00, 0.27–0.30, 0.51–0.56 and 0.95–1.01 were prepared through the interaction of AlCl3, or-thosilicic acid and NaOH solutions. When these solutions reacted with <2 µm sized vermiculite (Vt) and montmorillonite (Mt), varying amounts of Al and Si were fixed on Vt and Mt clays. Potassium fixation and exchange capacities of HyA/HAS (OH/Al = 1.0, 2.0 and 2.5)-Vt and HyA/HAS (OH/AI = 2.0)-Mt complexes were compared with those of untreated Vt and Mt at added K levels ranging from 21 to 319 cmolc kg−1. The untreated Vt clay showed K fixation as high as 94 cmolc kg−1, in contrast to only 16 cmolc kg−1 exchangeable K. The untreated Mt fixed a maximum of 9 cmolc K kg−1 out of a total K adsorption capacity of 67 creole kg−1. In the HyA/HAS-Vt complexes, K fixation reduced drastically in comparison to untreated Vt, and ranged from 9 to 24 cmolc kg−1 out of their total K adsorption capacities of 61 to 81 cmolc kg−1. In the HyA/HAS-Mt complexes, too, the amount of K fixed reduced to a great extent in comparison to Mt and ranged from 1.48 to 1.84 cmolc kg−1. Potassium became more exchangeable due to the presence of hydroxy-interlayers in the clays. The reduction in CEC and the well-known propping effects of hydroxy-cations’ islands in the interlayers might have hindered K fixation by the complexes. The relationships of maximum K fixing capacities of the HyA/HAS-Vt complexes with the amounts of Al, Si and Al + Si fixed on Vt were all exponential and negative. However, the amount of Al + Si or only Al fixed on Vt appeared to be the best indicator of K fixation capacities of hydroxyinterlayered Vt clay.

Minerals in surface environments form in both turbulent and non-turbulent systems. This study compares the properties of Al goethite formed from ferrihydrite at 60°C in 0.3 M KOH with and without mechanical stirring. Compared to the static system, stirring increased crystal order and needle thickness, decreased unit cell edge length a, but not b and c, reduced the separation between the 2 OH-bending vibrations, increased Al substitution and promoted hematite formation.

Lode, a dioctahedral illite-rich clay from Latvia belonging to the mica group of clay minerals, undergoes thermal transformation via a series of structurally disordered intermediate phases. Despite containing high levels of paramagnetic Fe substituted into the octahedral sites, 29Si and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectra of sufficient quality are obtained to resolve different structural units, showing clearly defined structural changes which occur in the sample during calcination to 1200 °C. However, Fe plays a significant role in broadening the Al signal, with integrated peak intensities decreasing as temperature increases. Significant differences are revealed in the thermal decomposition process by NMR spectra between pyrophyllite, Ca-montmorillonite and illite clays, possibly due to the different cations present in the interlayer. It has also been shown for illite that no structural differences at the atomic level occur when the dwell time at a particular temperature is varied and no difference is observed between samples that have different thermal histories; however, a minor effect of particle size and surface area is visible in the NMR data.

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.

The sorption capacity of hydrotalcite (HT) and its calcined product (CHT) was evaluated for 131I− sorption from water solution and it was determined as a function of the calcining temperature. The radionuclide content was determined by γ-spectrometry. Solids were characterized by thermal analysis, X-ray diffraction (XRD), electron microscopy and Brunauer-Emmett-Teller (BET) analysis. For 0.1 M Na I solution, labeled with 131I−, sorption capacity was found to be 0.24 meq g−1 (7.2% of the anion exchange capacity, AEC). But, if the sample was previously calcined at 773 K and the HT structure destroyed, the sorption of I− increased considerably, up to 2.08 meq g−1 (63% of the AEC) and the HT structure was reconstructed. The 131I− sorption at very low concentrations (10−14M) was 0.04 × 10−14 meq of 131I− g−1 in the noncalcined HT, but for calcined samples at 773 K, the sorption increased to circa 0.97 × 10−14 meq g−1. Calcination temperature determines the surface area of the resulting mixed oxides, and that property seems to be the most important factor controlling the I− sorption. If the calcination temperature was increased to 873 K, the specific surface area of the oxide mixture increased and I− sorption increased as well, whereas calcination of HT at 973–1073 K resulted in a low surface area and a low I− retention.

The thicknesses of fundamental illite particles that compose mixed-layer illite-smectite (I-S) crystals can be measured by X-ray diffraction (XRD) peak broadening techniques (Bertaut-Warren-Averbach [BWA] method and integral peak-width method) if the effects of swelling and XRD background noise are eliminated from XRD patterns of the clays. Swelling is eliminated by intercalating Na-saturated I-S with polyvinylpyrrolidone having a molecular weight of 10,000 (PVP-10). Background is minimized by using polished metallic silicon wafers cut perpendicular to (100) as a substrate for XRD specimens, and by using a single-crystal monochromator. XRD measurements of PVP-intercalated diagenetic, hydrothermal and low-grade metamorphic I-S indicate that there are at least 2 types of crystallite thickness distribution shapes for illite fundamental particles, lognormal and asymptotic; that measurements of mean fundamental illite particle thicknesses made by various techniques (Bertant-Warren-Averbach, integral peak width, fixed cation content, and transmission electron microscopy [TEM]) give comparable results; and that strain (small differences in layer thicknesses) generally has a Gaussian distribution in the log-normal-type illites, but is often absent in the asymptotic-type illites.

Hydrothermal treatment of aqueous mixtures of sodium hydroxide, copper chloride and excess sodium silicate (Si/Cu ≥ 2) at 150 °C produced blue powders. Scanning electron microscopy/energy dispersive X-ray (SEM/EDX) analysis of the products show they all had similar chemical compositions, with Si/Cu ratios of approximately 1.33, the value expected for 2:1 trioctahedral phyllosilicates. Their X-ray diffraction (XRD) patterns were consistent with that of swelling smectite-type clays. Reaction mixtures that did not contain excess Si (Si/Cu ≤ 1.33) did not produce smectites. They gave gray mixtures of amorphous silicates and copper oxides, with some phyllosilicates. A mixture containing a Si/Cu ratio of 5.2 heated at 250 °C under 500 psi of Ar gave a pale blue solid containing a Si/Cu ratio of approximately 1, the value expected for chrysocolla. Transmission electron microscopy (TEM) showed this product had a well-ordered layered structure. Its XRD powder pattern was consistent with that of chrysocolla. This clay did not swell very much on exposure to glycol vapors. Peaks were observed in the cyclic voltam-mogram of electrodes modified with films of these synthetic Cu-clays. They were attributed to electrochemical activity of Cu(II) centers in the lattice of the clays. The presence of these redox active Cu(II) sites greatly improved charge transport in the films. Much larger voltametric waves were observed for [Os(bpy)3]2+ ions (“bpy” = the ligand 2,2′bipyridyl) adsorbed in films of the synthetic Cu-clays than in films of a natural montmorillonite. The larger peak currents obtained corresponded to 10- to 15-fold increases in the fractions of the adsorbed ions that were electrochemically oxidizable in the modified electrodes.