Several soil and reference smectites and vermiculites and one reference illite were examined by high-resolution transmission electron microscopy (HRTEM) to decipher the nanostructure and layer charge heterogeneity in these minerals. HRTEM results were compared with those obtained from powder X-ray diffraction (XRD) analysis. Samples were either exchanged with Na+ ions followed by equilibration with a very dilute solution of NaCl in a pressure membrane apparatus at 316 hPa (pF = 2.5) to see the effect of hydration and applied pressure on layer organization, or exchanged with dodecylammonium ions to see the expansion behavior. Oriented samples were embedded in a low viscosity resin and cut approximately 500 Å thick perpendicular to d(001) using an ultramicrotome fitted with a diamond knife. In general, Na-saturated soil clays possessed crystallites that were thinner (c-direction) and shorter (ab-direction) as compared with reference clays. In all cases, samples treated with dodecylammonium chloride exhibited nanostructures that were more disintegrated as compared with Na-saturated samples. In a soil vermiculite, dodecylammonium ion exchange showed frayed edges indicating the initiation of mica transformation to vermiculite from edge toward core. In a reference vermiculite (Transvaal) treated with dodecylammonium ions, in addition to completely expanded crystallites, a regular interstratification between expanded vermiculite and mica (phlogopite) layers was clearly observed in some crystallites. Such nanostructural details were not detected by XRD. HRTEM of the Na-treated illite showed thick crystallites having 10 Å layer separations, whereas the dodecylammonium-exchanged illite showed three types of layers with different degrees of expansion indicating charge heterogeneity in illite: 1) unexpanded (10 Å, highest charge) crystallites; 2) expanded high-charge vermiculite-like (24 Å) crystallites; and 3) occasionally expanded high-charge vermiculite-like (24 Å) layers interspersed in the matrix of 10Å crystallites.

The Dongrae fault within the Yangsan fault system is considered one of the major faults in the southeastern part of Korea, extending over 150 km. The results of K-Ar radiogenic dating of fault gouges collected from six localities show a relatively wide range in age from 57.5 million years ago (Ma) to 40.3 Ma. Fault gouges are composed of newly formed minerals, including smectite, illite, zeolite, kaolinite, K-rich feldspar, apatite, and pyrite. The occurrence of abundant smectite and illite-lMd with lesser quantities of zeolite suggests that the fault gouges experienced hydrothermal alteration at low temperatures. Smectite is probably unstable relative to other clay minerals, such as illite and zeolite. Considering that filiform mordenite is replacing the smectite, we suggest that mordenite formed by recrystallization involving a solid-state transformation. Under high fluid/rock ratios, smectite seems to have formed in the early stage of alteration. In contrast, zeolite minerals and authigenic K-rich feldspar progressively appeared with time as the fluid/rock ratio decreased with the changing chemistry of the hydrothermal fluids. The composition of clay minerals in the gouge materials probably was controlled by the chemistry and the amount of circulating fluids derived from adjacent granitic rocks.

In order to remove impurities, natural illite is often subjected to chemical pretreatments before analysis, the assumption being that such pretreatments have little or no effect on the composition of illite. Bulk analyses are sometimes reported before and after pretreatment (Aja et al. 1991) but, because the contribution of the impurities to the bulk composition is unknown, the possible effects of chemical pretreatments on the composition of illite cannot be assessed. Recently, Rosenberg and Hooper (1996) have shown that analytical transmission electron microscopy (ATEM) techniques, which exclude impurities, can be used to determine the bulk compositions of relatively pure illite by averaging the analyses of at least 50 crystals per sample. This approach can be applied to impure illite in order to determine the effect of chemical pretreatments on the composition of natural illite.

The adsorption and degradation of the herbicide triasulfuron [2-(2-chloroethoxy)-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide] (CMMT) on homoionic Fe3+-, Al3+-, Ca2+-, or Na+-exchanged montmorillonite in aqueous medium were studied. Ca- and Na-exchanged montmorillonite were ineffective in the adsorption and degradation of triasulfuron. The adsorption on Fe-and Al-exchanged montmorillonite was rapid, and equilibrium was attained after 5 min. Degradation of the herbicide was slow and the type of the degradation products depended on the nature of the exchangeable cations. In the presence of Fe3+-rich montmorillonite, the metabolites 2-(2-chloro-ethoxy)benzenesulfonamide (CBSA), 2-(2-chloroethoxy)-N-[[(4-hydroxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide (CHMT), and l-[2-(2-chloroethoxy)benzene-l-sulfonyl]-7-acetyl-triuret (CBAT) were the only identified products, whereas 2-amino-4-methoxy-6-methyltriazine (AMMT), CBSA, CHMT, and CBAT were the primary metabolites for the Al3+-rich montmorillonite. A Fourier transform infrared (FT-IR) study of montmorillonite samples after the interaction with triasulfuron in organic solution suggests that the hydrolysis mechanism involves the adsorption of the herbicide on the 2:1 layers.

The corrensite from a chlorite vein-like rodingite blackwall in serpentinites has been studied. The proper identification of swelling layers in corrensite using heating at 500°C was ambiguous because of the spontaneous rehydration. Even K+-saturated samples heated to 500°C readily rehydrated after being cooled. This can be prevented if XRD patterns are recorded at 300°C, without cooling the sample. A standard heating at 500°C can result in partial decomposition of brucite-like sheet as evidenced by ASN simulation.

The ASN-calculated XRD patterns of contracted corrensite proved that an inhomogeneous distribution of heavy atoms (Fe, Ni, Mn, Cr etc.) between brucite-like sheet and talc-like layers and between two adjacent corrensite units in the interstratified mineral may result in the disappearance of low angle reflections (24 Å and 12 Å), which can lead to miscellaneous interpretation if distribution of heavy cations is not checked.

The corrensite occurred together with regular chlorite. However, it is assumed to be formed due to direct crystallization from late hydrothermal solutions as deduced from comparison of the Mg/(Mg + Fe) ratio in the corrensite, serpentinite and chlorite.

In this paper atomic force microscopy-studies are reported suggesting the existence of vicinal faces on the (100) plane of artificially grown goethite. Goethite crystals are commonly regarded to have boundary planes of (100), (010) and (001) faces. In contradiction to these theoretical models TEM and SEM images exhibit (110) and (021) faces to be dominating. These goethite particles consist of many crystallographic coherent domains so that the existence of dislocations on the surfaces has to be assumed. These sites on the surfaces may serve as a nucleation site for the formation of steps. The vicinal faces on the (100) face found with the AFM are (021) faces. They influence the growth velocity of the (100) face to such a degree, that this face vanishes and only (110) faces remain as stable boundary surfaces. The (021) faces are also stable, but have the highest growth rate among the faces considered.

A critical demand in environmental modeling and a desirable but elusive goal of research on the ion exchange properties of the charged solid surface has been to determine the selectivity coefficient from fundamental properties of the ions and surface. We developed a Hard and Soft Acid and Base (HSAB) Model to describe exchangeable cation selectivity on solid surfaces. Our previous work has shown that the model quantitatively describes alkali cation exchange on clay minerals in terms of the absolute electronegativity and softness of the exchangeable cations and two fitting parameters: α and β. This study was conducted to determine the relationship between α and β and surface charge characteristics of 2:1 clays. The layer charge and cation selectivity of seven smectites and one vermiculite were used. The regression of log Kvo against four combinations of charge properties was performed and the appropriate relationship between α, β, and surface charge was selected based on both statistical criteria (R2) and their consistency with the assumptions of the HSAB model. The selected model was then cross-validated using separate cation exchange data from the literature. It was found that α and β are linearly related to the amount of charge arising from mineral tetrahedral and octahedral sites, respectively. These results make it possible to predict the alkali cation selectivity of 2:1 clay minerals from their chemical composition data and the alkali cation properties.

The quantification of the relative mineralogical composition of clay mixtures by powder X-ray diffraction or chemical mass balance methods has been severely hampered by a lack of representative standards. The recent development of elemental mass balance models that do not require standards for all minerals in the mixture may help circumvent this problem. These methods, which are based on the numerical optimization of systems of non-linear equations using the Marquardt algorithm, show promise for mineral quantification. The objective of this study is to make a preliminary assessment of the accuracy of these methods and to compare them to linear models that require standards for all mineral phases. Methods 1 and 2 are based on weighted average solutions to simultaneous linear equations solved for single samples with known standards. Solutions were achieved by a matrix decomposition algorithm and the Marquardt algorithm, respectively. Methods 3 and 4 are based on a set of simultaneous non-linear equations with reduced non-linearity solved by least squares optimization based on the Marquardt algorithm for multiple samples. Illite and halloysite compositions were fixed in Method 3, only the halloysite composition was fixed in Method 4. All models yielded relative weight fractions of the three mineral components; additionally, Methods 3 and 4 yielded compositions of smectite, and smectite and illite, respectively. Ten clay mixtures with varying proportions of the <0.2 μm size fraction of three different reference clays (Wyoming bentonite, Fithian illite, and New Bedford halloysite) were prepared gravi-metrically and analyzed by inductively coupled plasma-atomic emission spectroscopy. Accuracy of the four methods was evaluated by comparing the known mineralogical compositions of the mixtures with those predicted by the models. Relative errors of 5 and 10% (randomly +/-) were imposed on the elemental composition of the smectite standard to simulate errors due to lack of good standards. Not surprisingly, the accuracy of Methods 1 and 2 decreased rapidly with increasing error. Because Methods 3 and 4 optimized for the smectite composition and only used it for an initial guess, they were unaffected by the level of introduced error. They accurately quantified the mineralogical compositions of the mixtures and the elemental compositions of smectite, and smectite and illite, respectively.

A comparative study is reported in which kaolinite has been hydrothermally synthesized at several pH conditions. The syntheses were carried out at 220 °C for 3 to 10 d with distilled water or acidic solutions using a mixture of silica-gel derived from alkoxide and gibbsite with a Si/Al ratio of 1:1 as the starting material. Use of acidic solution for the synthesis promotes the dissolution of the starting materials and leads to kaolinitization at an earlier stage of the reaction. However, the rate of kaolinitization is found to be rather slow, in comparison to the reaction with distilled water. The synthetic kaolinite was characterized by X-ray powder diffraction pattern. Kaolinite synthesized with distilled water was poorly grown for direction of the stacking. For example, crystallite size along the c*-axis = 155 Å, whereas kaolinite synthesized with acidic solution gave a higher crystallite size along the c*-axis, such as 253 Å in the case of the synthesis with 0.1 N HCl. Hinckley index of the synthetic kaolinite was varied from 0.35 to 0.80 by the acidity of the reaction. Different kaolinitization processes are implied by differences observed in the rate of kaolinitization, which has an influence on the nature of the stacking faults of the kaolinite.

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.

Small-angle X-ray scattering (SAXS), adsorption and nuclear magnetic resonance (NMR) techniques were used to determine the fractal dimensions (D) of 3 natural reference clays: 1) a kaolinite (KGa-2); 2) a hectorite (SHCa-1), and 3) a Ca-montmorillonite (STx-1). The surfaces of these clays were found to be fractal with D values close to 2.0. This is consistent with the common description of clay mineral surfaces as smooth and planar. Some surface irregularities were observed for hectorite and Ca-montmorillonite as a result of impurities in the materials. The SAXS method generated comparable D values for KGa-2 and STx-1. These results are supported by scanning electron microscopy (SEM). The SAXS and adsorption methods were found to probe the surface irregularities of the clays while the nuclear magnetic resonance (NMR) technique seems to reflect the mass distribution of certain sites in the material. Since the surface nature of clays is responsible for their reactivity in natural systems, SAXS and adsorption techniques would be the methods of choice for their fractal characterization. Due to its wider applicable characterization size-range, the SAXS method appears to be better suited for the determination of the fractal dimensions of clay minerals.

Shortly after construction of a subdivision in the southwest Denver metropolitan area in 1986, a portion of the subdivision built directly on steeply-dipping strata of the Pierre Shale began experiencing damaging differential movements, causing house foundations to fail and pavements to warp and crack. This formation is a Late Cretaceous marine clay-shale composed predominantly of fluvial mixed-layer illite/smectite and quartz. During deposition of the shale, periodic and explosive volcanism generated thin beds of bentonite, consisting initially of volcanic ash and subsequently altered to nearly pure smectite. Some of these bentonite beds were exposed in a trench adjacent to the subdivision and perpendicular to the strike of the steeply-dipping strata. The thickest bentonite beds correlated well with linear heave features that these beds parallel the bedrock strike throughout the subdivision were mapped via severely deformed pavements. Mineralogical data show the bentonite bed that correlates with the worst damage within the subdivision consists of about 62% smectite by weight with mixed-layer illite/smectite expandability of 92%. By comparison, a sample of the typical silty claystone, which is fluvial mixed-layer illite/smectite mixed with detrital quartz from the adjacent strata, had about 23% smectite by weight with 70% to 90% illite/smectite expandability. Geotechnical tests for swell potential show that samples of 2 bentonite beds swelled 39% to 43% compared to 2% to 8% for samples of the typical silty claystone. It is proposed that differential swell resulting from stratigraphically-controlled differences in clay mineralogy and grain-size is the primary factor controlling extreme damage for this geologic setting.

Novel promising modified clays adsorbents were synthesized by intercalating hydroxy-Al polymer associated with poly(ethyleneoxide) in the interlayer of montmorillonite. Two different PEOs of low molecular weight (600) and high molecular weight (100,000) were used. In both cases, the resulting materials are hydrolytically stable and display a slightly better crystallinity than the materials prepared in the absence of PEO. Thermal analysis and infrared spectroscopy indicate changes in the PEO molecular conformation after intercalation revealing interactions between the polycations and the organic molecules. The chain length of the polymer has a strong influence on the surface area of the pillared materials obtained after calcination at 500°C. The use of the high molecular weight polymer leads to products with a higher specific surface area (about 400 m2/g) whereas the lower molecular weight compound does not modify significantly the surface areas. This behavior can be explained by the different nature of the species intercalated in the interlayer. PEO(600) leads to isolated organometallic species whereas PEO(100,000) seems to lead to a network of complexed polycations linked by ethylene oxide units. In the case of the PEO(100,000), high amounts of polymer in the pillaring solution provoke a partial dissolution of the octahedral layer of the clay.

Transmission electron microscopy (TEM) and analytical electron microscopy (AEM) methods were used to study the crystal chemistry of phyllosilicates occurring in green grains of Miocene sediments from the Congo continental shelf. Using diagrams based on wt. % K and the (Fe + Mg)/Al ratio, minerals were distinguished from mixed-layer phases. The most abundant detrital mineral is Fe-kaolinite. The morphology and composition identify this mineral as a component of ferralitic soils. This Fe-rich kaolinite has undergone a complex process of partial dissolution and recrystallization and further enrichment in Fe and, to a lesser extent, in Mg in the marine environment. The detrital mica observed with TEM retains the original morphology and chemistry of muscovite. Alteration processes resulted in the crystallization of 1:1 trioctahedral Fe2+ and Mg-rich minerals and interstratified phases with 1:1 and 2:1 layers in varying proportions observed with the aid of high-resolution transmission electron microscopy (HRTEM) imaging. Included among the newly formed 7-Å phases are those apparently containing excess Si. The smectites are apparently neoform, and chemical analyses showed that these marine K-smectites belong to the beidellite-nontronite series and have tetrahedral substitutions similar to muscovite. Their compositions are closer to beidellite than to nontronite, although the latter was observed in association with goethite. The TEM observations and crystallochemical data show that mineral alteration ceased after forming mixed-layer minerals, and alteration did not reach the glauconitization stage. Apparently, the Miocene assemblages experienced rapidly changing environmental conditions and high sedimentation rates that continue today.

The nature, composition, and relative abundance of clay minerals in the sandstones of the Brent Group reservoir were studied between 3200–3300 m in a well of the Ellon Field (Alwyn area, North Sea). The sandstones have a heterogeneous calcite cement which occurred during early-diagenesis. Clay diagenesis of the cemented and uncemented sandstones was investigated using optical microscopy, scanning electron microscopy (SEM), X-ray diffraction analyses (XRD), and infrared spectroscopy (IR). The influence of cementation on clay neoformation is demonstrated in this study. Detrital illite and authigenic kaolinite are present in both the calcite-cemented and uncemented sandstones suggesting that kaolinite precipitated before calcite cementation. In the uncemented sandstones, blocky dickite replaces vermiform kaolinite with increasing depth. At 3205 m, authigenic illite begins to replace kaolinite and shows progressive morphological changes (fibrous to lath-shape transition). At 3260 m, all sandstones are not cemented by calcite. Illite is the only clay mineral and shows a platelet morphology.

In the cemented samples, vermiform kaolinite is preserved at all depths, suggesting that dickite transformation was inhibited by the presence of the calcite cement. This observation suggests that calcite cement would prevent fluid circulation and dissolution-precipitation reactions.

Clay samples of greenish colour were collected from submarine hydrothermal chimneys of the Galapagos Rift and Mariana Trough. Mineralogical and chemical investigations of the clay by scanning and transmission electron microscopy, X-ray diffraction, differential thermal analysis, infrared-spectros-copy, X-ray fluorescence, and determination of specific surface area, and oxygen isotope composition identify it as a well crystallized nontronite. This nontronite of hydrothermal origin has a nearly monomineralic character, a low Al-content, and a formation temperature of 21.5 to 67.3°C. The most remarkable characteristic, however, of the nontronite deposit is its microstructure, a network of microtubes composed of fine frequently folded clay sheets. These delicate filaments show close similarity in size and form to sheath forming bacteria. The correlation between clay mineral and chemical characteristics, as well as biological conditions at marine hydrothermal smoker chimneys, let us suggest that Fe oxidizing, sheath forming bacteria are playing a decisive role in nontronite formation at these sites.

Illitization of smectite during progressive burial diagenesis occurs differently in sandstone and mudstone, which are interbedded in the sedimentary sequence of the Niigata basin. Reaction progress of illitization of smectite via mixed-layer illite-smectite (I-S) in the mudstone is more complete than in the sandstone. In sandstone, smectite converts to (Reichweit, R ≥ 3) I-S and illite via random (R = 0) I-S to ordered (R = 1) I-S, and authigenic chlorite and quartz form as products of the illitization of smectite.

The original composition of detrital smectite and the occurrence of Na+, K+, Ca2+, Mg2+, and Fe2+ in pore fluids partly control both illitization of smectite and the resulting authigenic mineral products in the diagenetic process. In mudstone, detrital smectite is K- and Si-rich in composition, and the illitization of smectite indicates that the original composition is mostly inherited. Excess silica owing to illitization is released to produce authigenic quartz. In sandstone, smectite forms primarily by precipitation. The evolving compositions produced by early illitization form smectite, then random (R = 0) I-S, and then ordered (R = 1) I-S. These transitions are related to compositions of pore fluid. Changes in K/(K + Ca + Na) vs. K + Ca + Na imply that the increase of interlayer cations occurs by absorption and smectite transforms to random (R = 0) I-S, followed by the exchange of interlayer cations to ordered (R = 1) I-S with increasing diagenetic grade. Late illitization from (R = 1) I-S to R ≥ 3 suggests decomposition of smectite and early I-S with an increase in the number of illite layers. Dissolution experiments of host rocks with pure water and 0.01 M HCl solution reflect the differences in chemistry of the original pore fluid and authigenic carbonate in the process of diagenesis of clastic rocks. These results explain how chemical composition produces large variations in transformation temperature of smectite to illite in the diagenetic process.