The provenance of clays in shaley intervals across the Permian-Triassic boundary (PTB) in the Xiakou section was investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM), and the results suggest that the layers have three different provenances. The layer P267-b has a loose texture with an oriented arrangement of detrital clay particles, consisting mainly of illite and minor chlorite with irregular outlines or ragged edges. The dehydroxylation reaction of the clays in this layer is characterized by an intense overlapping endothermic effect at ∼600°C, produced by mixed-layer illite-smectite (I-S) consisting of a mixture of cis-vacant (cv)and trans-vacant (tv) octahedral sheets derived from weathering of detrital illite. Layer P259-b shows a more condensed texture with a dark color, and is composed mainly of I-S and minor illite and chlorite. Evidence for alteration of detrital materials to clay mineral aggregates was observed under SEM. Similar to layer P267-b, an intense dehydroxylation reaction occurs at ∼600°C, indicating clays consisting of a mixture of tv and cv sheets and, therefore, that the sediments were derived from a mixture of terrigenous and volcanic sources, combining the texture and the clay-mineral composition of those sediments. However, the undisturbed lamination and relatively small grain size in this bed indicate a low-energy depositional environment. The clay-mineral compositions of the other layers are mainly of I-S with minor amounts of illite and chlorite. Their endothermic dehydroxylation reaction, however, occurs mainly at ∼660°C, indicating that cv sheets are dominant in the clays, and thus, are derived from smectites of volcanic origin. Observations by SEM show that clay minerals grow at the expense of detrital materials, confirming the diagenetic alteration of volcanic ashes in marine sediments. Illite and chlorite are the detrital clay minerals in the clay layers across the PTB in the Xiakou section. The presence of detrital illite and chlorite in the sediments means that an arid climate prevailed in the region during the end-Permian and early Triassic period.

To further elucidate adsorption-to-partition transitional mechanisms which have been proposed previously for organo-bentonites with different surfactant loadings, the structural characteristics of interlayer surfactant aggregates on organo-bentonite with different surfactant cetyltrimethylammonium bromide loading levels (0.20–2.56 times cation exchange capacity, CEC) have been investigated by in situ X-ray diffraction (XRD) and Fourier TransformInfrared (FTIR) spectroscopy. The sorption properties and the structure of the clay interlayers changed according to the type of surfactant, the surfactant loading level, and the state of hydration in the clays. Based on the sorption of nitrobenzene, phenol, and aniline to organobentonites, the contaminant sorption coefficients (Ksf), normalized with the organic carbon content, show a remarkable dependence on surfactant loading levels. The Ksf values first increased with surfactant loading until reaching a maximum at 1.0 to 1.2 times the CEC, and then decreased. According to the theoretical calculation of the volume fractions relating to the interlamellar space, the interlamellar microenvironment became a more hydrophobic medium, contributing to the dissolution of organic contaminants, as the surfactant loading increased from 0.20 to 2.56 times the CEC. However, the increase in packing density (ρ) for the intercalates, and induced steric hindrances both affect the result in terms of a reduction in the accessible free space where the organic contaminants can be located, which might be a negative factor in the sorption capacity.

The total specific surface area (TSSA) and smectitic layer charge (Qs) calculated from the structural formulae and unit-cell dimensions of 12 pure smectite samples were used as a reference in the design and evaluation of TSSA and Qs measurement techniques based on cation exchange capacity (CEC), H2O retention at 47% RH, and ethylene glycol monoethyl ether (EGME) retention. A thermogravimetric analysis-mass spectrometry (TGA-MS) technique was used to study the release of H2O from smectite on heating, and to introduce a correction for H2O remaining in the smectite after heating to 110°C, because the sample weight at this temperature has been used routinely as a reference in CEC and EGME sorption measurements. A temperature of 200°C was found to be the optimum reference for such measurements.

A good agreement between Qs from the structural formula and from CEC was obtained when this correction was applied. The TSSA of smectite was measured with similar accuracy (mean error of ±5–7%) by three techniques: (1) using mean H2O coverage; (2) using mean EGME coverage; and (3) using a combination of H2O coverage and CEC. A reduction of the mean error from 5–7% to 4% can be obtained by averaging these measurements, and a further reduction to 3% by introducing corrections for the dependence of H2O and EGME coverage on layer charge. The study demonstrates that Ca2+-smectite samples at 47% RH have H2O contents corresponding to 88–107% of the theoretical mass of a monolayer and offers an explanation of this variation.

Clay minerals impart important chemical properties to soils, in part, by virtue of changes in the redox state of Fe in their crystal structures. Therefore, measurement of Fe(III)/Fe(II) and partitioning of Fe(II) in different reactive sites in clay minerals (during biological and chemical Fe(III) reduction) is essential to understand their role and their relative reactivity in terms of reduction and immobilization of heavy metal contaminants such as technetium. This study had three objectives: (1) to understand the degree of dissolution of nontronite (Fe-rich smectite) as a result of chemical and biological reduction of Fe(III) in the structure; (2) to quantify partitioning of chemically and biologically produced Fe(II) into different reactive sites in reduced nontronite, including aqueous Fe2+, ammonium chloride-extractable Fe(II) (mainly from the ion-exchangeable sites, denoted as $\text{Fe}{\left(\text{II}\right)}_{{\text{NH}}_4\text{Cl}}$${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$), sodium acetate-extractable Fe(II) (mainly from the surface complexation sites, denoted as Fe(II)acetate), and structural Fe(II) (denoted as Fe(II)str); and (3) to evaluate the reactivity of these Fe(II) species in terms of Tc(VII) reduction. Chemical and biological reduction of Fe(III) in nontronite (NAu-2) was performed, and reduced nontronite samples with different extents of Fe(III) reduction (1.2–71%) were prepared. The extent of reductive dissolution was measured as a function of the extent of Fe(III) reduction. Our results demonstrated that chemically and biologically produced Fe(II) in NAu-2 may be accommodated in the NAu-2 structure if the extent of Fe(III) reduction is small (< ∼30%). When the extent of reduction was >∼30%, dissolution of nontronite occurred with a corresponding decrease in crystallinity of residual nontronite. The Fe(II) produced was available for partitioning into four species: ${\text{Fe}}_{\left(\text{ab}\right)}^{2+}$${\rm{Fe}}_{\left( {{\rm{ab}}} \right)}^{2 + }$, Fe(II)acetate, $\text{Fe}{\left(\text{II}\right)}_{{\text{NH}}_4\text{Cl}}$${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$, and Fe(II)str. The increase in Fe(II)acetate during the early stages of Fe(III) reduction indicated that the Fe(II) released had the greatest affinity for the surface-complexation sites, but this site had a limited capacity (∼60 µmol of Fe(II)/g of NAu-2). The subsequent increase in $\text{Fe}{\left(\text{II}\right)}_{{\text{NH}}_4\text{Cl}}$${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$ indicated that the released Fe(II) partitioned into the exchangeable sites once the amount of Fe at the surface-complexation sites reached half of its maximum site capacity. The fraction of Fe(II)str decreased concomitantly, as a result of Fe(II) release from the NAu-2 structure, from 100% when the extent of Fe(III) reduction was <30% to nearly 65% when the extent of Fe(III) reduction reached 71%. The Fe(II)acetate and Fe(II)str exhibited greater reactivity in terms of Tc(VII) reduction than the $\text{Fe}{\left(\text{II}\right)}_{{\text{NH}}_4\text{Cl}}$${\rm{Fe}}{\left( {{\rm{II}}} \right)_{{\rm{N}}{{\rm{H}}_4}{\rm{Cl}}}}$. Clearly, the surface-complexed and structural Fe(II) are the desirable species when reduced clay minerals are used to reduce and immobilize soluble heavy metals in contaminated groundwater and soils. These results have important implications for understanding microbe—clay mineral interactions and heavy metal immobilization in clay-rich natural environments.

The state and dynamics of water and cations in pure and mixed Na-Cs-montmorillonite as a function of the interlayer water content were investigated in the present study, using Monte Carlo and classical, molecular-dynamics methods. While highly idealized, the simulations showed that the swelling behavior of hetero-ionic Na-Cs-montmorillonite is comparable to the swelling of a homo-ionic Na- or Cs-montmorillonite. The mixed Na-Cs-montmorillonite is characterized by intermediate interlayer distances compared to homo-ionic Na- and Cs-montmorillonites. Dry, hetero-ionic Na-Cs-montmorillonite is characterized by a symmetric sheet configuration, as is homo-ionic Cs-montmorillonite.

We found that at low degrees of hydration the absolute diffusion coefficient of Cs+ is less than for Na+, whereas at greater hydration states the diffusion coefficient of Cs+ is greaterthan for Na+. An analysis of the relative diffusion coefficients (the ratio between the diffusion coefficient of an ion in the interlayer and its diffusion coefficient in bulk water) revealed that water and Na+ are always less retarded than Cs+. With large interlayer water contents, tetralayer or more, Na+ ions preferentially form outer-sphere complexes. The mobility perpendicular to the clay surface is limited and the diffusion is equivalent to two-dimensional diffusion in bulk water. In contrast, Cs+ ions preferentially form ‘inner-sphere complexes’ at all hydration states and their two-dimensional diffusion coefficient is less than in bulk water.

The question remains unanswered as to why experimentally derived relative diffusion coefficients of Cs+ in the interlayer of clays are about 20 times less than those we obtained by classical molecular dynamics studies.

Very unusual rocks consisting of natrolite (>95 vol.%) ± pargasite (<5 vol.%) and rarealbite (<1 vol. %) have been discovered in the Kop mountain range, eastern Turkey. We propose to call these rocks ‘natrolitite’ and ‘pargasite natrolitite’. They were produced by Na Si metasomatism of dikes and stocks of diorite through replacement of the intermediate primary igneous plagioclase to produce natrolite. The metasomatic alteration produced concentric elliptical zones characterized by distinct mineral assemblages centered on intrusions of diorite. The Central Zone 1 consists of variably albitized diorite with preserved magmatic textures (albite ± andesine ± pargasite ± quartz). Transition Zone 2 comprises natrolite-bearing diorite (natrolite ± albite ± andesine ± pargasite ± calcite ± quartz). Marginal Zone 3 is a rock made up almost entirely of natrolite (natrolite ± pargasite ± albite ± calcite ± chlorite). Outer Zone 4 occurs along the boundary between the natrolitite and the surrounding serpentinite and consists of listvenite, a rock which comprises magnesite, quartz, calcite, mica, talc, and hematite, indicating a role for CO2 in the metasomatic reactions, consistent with the presence of calcite in the alteration zones. Zone 5 consists essentially of brecciated serpentinite with numerous hydrothermal quartz veins and calcite veins. Whole-rock compositions document an increase in Na2O, Al2O3, and H2O from the core (central zone) to themargin while CaO, MgO, and SiO2 decrease. Plagioclase abundance and composition also varies outwards from the central core rocks where it occurs as a primary magmatic phase (∼95 vol.% An41−38) to the alteration zones (<5 vol.% An32−37) due to partial to complete replacement of plagioclase by natrolite with or without rare albite. The natrolites exhibit little variation in Si/Al ratios, ranging between 1.45 and 1.61, and are similar in composition to those reported in the literature. Accompanying pargasitic amphibole also becomes progressively more sodic in composition from the core rocks to the marginal zone rocks. Our analysis indicates that albitization preceded the formation of natrolite and that the formation of natrolite, instead of other more typical alteration minerals (e.g. analcime and paragonite), reflects Na metasomatism at lower chemical potentials for Al2O3 and SiO2. Potential sources of Na could be hypersaline brines or leaching of country rocks, such as trondhjemites. The fluids were driven in hydrothermal convection cells set up by theintrusion of thediorites.

TheAu-Cu (±Pb, Zn, Ag) prospects of Lavras do Sul, southernmost Brazil, arehosted in Neoproterozoic granitic and volcanogenic rocks. Mineralization occurs in structurally controlled N40°W to E-W quartz veins; sericite (±chlorite) and sulfides are the main secondary minerals in associated wall rocks.

In the present contribution we use petrography (optical microscopy and scanning electron microscopy (SEM)), mineralogy (X-ray diffraction (XRD) with polytypes, FWHM, decomposition of diffraction patterns), and crystal chemistry of samples from several prospects to document the spatial and temporal evolution of sericitic alteration of veins and wall rocks associated with gold.

Hexagonal, coarse-grained 2M1 phengite-rich alteration (± illite) is best developed with coarse-grained primary growth (comb) quartz + pyrite ± Au veins and altered wall rock from the western portion of the granitic complex (phyllic alteration). Pure phengite was recognized by narrow XRD profiles (FWHM ⩽ 0.2°2θ CuKα) of the <5 µm particle-size fraction, non-expandable d001 X-ray reflections and interlayer charge (IC) >0.9 per O10(OH)2.

Towards the eastern zones of the granitic complex and in the volcanogenic rocks, wider XRD profiles (FWHM values ⩾ 0.2°2θ CuKα) were decomposed. They contain mixtures of coarse- to fine-grained, lath-like crystals of both 2M1 and 1M illite (non-expandable d001 X-ray reflections, IC between 0.85 and 0.89 per O10(OH)2) with expandable d001 reflections associated with lath-like, fine-grained crystals of ordered (R ⩾ 1) illite-rich I-S (80–90% of illite; IC of ∼0.8 per O10(OH)2), and minor amounts of regularly ordered (R = 1), illite-rich I-S mixed layers (75% of illite; IC of ∼0.74 per O10(OH)2). The dioctahedral clay association of illite + illite-rich I-S mixed layers (intermediate argillic alteration) is best developed in quartz + pyrite ± Au veins, breccias, and wall-rock alteration from the eastern portion of the granitic complex and in the volcanic area. Quartz from veins and breccias has fine-grained primary growth, recrystallization, and replacement textures, similar to those in epithermal deposits.

The overall distribution of the dioctahedral clays indicates that the study area represents a fracture-controlled, tilted, porphyry to epithermal deposit, with telescoping alteration features observed in the east of the mining district. Deeper levels of exposure of a large hydrothermal system are observed in the west of the mining district, as shown by higher-rank dioctahedral minerals (phengite) that crystallize at relatively high temperatures (Tphe ≈ 300°C, phyllic alteration) associated with coarse-grained, primary-growth quartz veins, similar to those observed in porphyry deposits. On the other hand, shallower levels of exposure are observed in the east of the study area, associated with abundant, lower-rank dioctahedral clay minerals (illite + illite-rich I-S mixed layers, intermediate argillic alteration) that crystallize at relatively lower temperatures (TI-S ≈ 120–200°C).

Available data show that gold is associated with phengite, but that lower-rank, overprinting alteration characterized by illite-I-S may have locally modified the original gold grades.

Caliche in various forms, namely powdery, nodule, tube, fracture-infill, laminar crust, hard laminated crust (hardpan), and pisolitic crust, is widespread in the Mersin area in southern Turkey. It generally occurs within and/or over the reddish-brown mudstone of the Kuzgun Formation (Tortonian, Miocene) and alluvial red soils of the Quaternary. The mineralogical distribution along representative caliche profiles was examined by X-ray diffraction, scanning electron microscopy, differential thermal analysis-thermal gravimetry, and chemical techniques. Calcite is the most abundant mineral associated with minor amounts of palygorskite in caliche samples, whereas smectite is prevalent mainly in the reddish-brown mudstone and alluvial red soils of the caliche parent materials and is associated with appreciable amounts of palygorskite. These minerals are also accompanied by trace amount of illite, quartz, feldspar, and a poorly crystalline phase. Palygorskite fibers and fiber bundles were developed authigenically on euhedral or subhedral calcite crystals of the caliche units and at the edges of smectite flakes in the caliche host-rocks or sediments. Intense, continuous evaporation of subsurface soil-water resulted in an increase in pH and the dissolution of detrital smectite within the red mudstones and alluvial red soils that enclose the isolated caliche forms, and caused an increase in the Al+Fe and Mg/Ca ratio, favoring the formation of palygorskite under alkaline conditions. The calcium required for caliche formation may have originated from eolian dust, detrital carbonate minerals, and/or other caliche materials, which are dissolved by carbonic acid.

Clayey soils are essential materials used to reduce hydraulic conductivity and pollutant migration, common at sites of waste disposal. This study investigates the possible use of a Tunisian soil as a lining material for disposal sites for acidic-fluoride wastes. A permeability test on a waste-solution sample (pH = 2.7) obtained from a disposal site in southern Tunisia was conducted over a period of about 2 years. The test results show that the permeability decreased with time until stabilized at 8.33 × 10−11 m/s. After the permeability test, the samples retrieved from the permeameter show a degradation state which varied with the thickness of the specimen. These samples can be classified into three zones (Z1: unaffected, Z2: moderately affected; and Z3: extensively affected). Physicochemical characterization of the three samples (Z1, Z2, and Z3), and of the original argillaceous soil, was by X-ray diffraction, Fourier transform infrared spectroscopy, differential thermal and thermal gravimetric analysis, 29Si and 27Al nuclear magnetic resonance, and N2-adsorption techniques. The original sample consists essentially of palygorskite, kaolinite, and quartz. Sample Z3 underwent complete dissolution of kaolinite which supports the precipitation of fluoroaluminate and the appearance of an X-ray amorphous silica phase. In samples Z1 and Z2, the soil adsorbs fluoride at a rate of ∼68.5 mg/g and is highly resistant to acidic attack.

Thirty six bentonite samples from 16 different locations were examined in order to demonstrate the applicability of a new Rietveld description approach for quantitative phase analysis. X-ray diffraction patterns of the bulk material were obtained and analyzed by the Rietveld method. The samples contain up to ten different minerals, with dioctahedral smectite as the major component. A model for turbostratic disorder of smectites was formulated inside a structure-description file of the Rietveld program BGMN. The quality of the refinements was checked using an internal standard mineral (10.0 or 20.0 wt.% corundum) and by cross-checking results with X-ray fluorescence (XRF) data. The corundum content was reproduced with only small deviations from the nominal values. A comparison of the chemical composition obtained by XRF and the composition as re-calculated from quantitative Rietveld results shows a satisfactory agreement, although X-ray amorphous components such as volcanic glasses were not considered. As a result of this study, the Rietveld method combined with the new structure model for turbostratic disorder has proven to be a suitable method for routine quantitative analysis of bentonites with smectites as the dominant clay minerals.