The Late Westphalian to Artinskian Haushi Group in the Sultanate of Oman consists of the glaciogenic Al Khlata Formation and the Gharif Formation which contains marginal marine, coastal plain, and fluvial sediments. The sequence was deposited during a global-warming event following the Permo-Carboniferous glaciation of Gondwana. Because of a varied subsidence history, these sediments range from the surface in the SE to almost 5000 m in the NW of the basin.

Mixed-layer illite-smectite (I-S) is an important constituent of the <2 µm size fraction of sandstone and shale samples in both formations at all depths. Different starting compositions lead to three distinct trends of illite layers in I-S versus temperature for different sedimentary environments and paleoclimatic conditions. The starting compositions of I-S at the surface range from an ordered I-S in the Al Khlata Formation to smectite-rich in the Upper+Middle Gharif members.

Physical, chemical and environmental factors were investigated as causes for the different starting compositions of I-S. Both formations share an identical burial history, paragenesis, thermal evolution, and source of detrital material. They differ only in environmental conditions during sedimentation. Thus, the variation in starting composition of I-S appears to be best explained by distinct weathering conditions during sedimentation of the three units. In particular, the expected low intensity of chemical weathering during glaciogenic conditions is marked by the presence of higher amounts of unstable volcanic and sedimentary rock fragments in the Al Khlata Formation.

Redox properties of iron-bearing mineral surfaces may play an important role in controlling the transport and transformation of pollutants into ground waters. Suspensions of seven iron-bearing minerals were reacted with pH and redox indicators under anaerobic conditions at the pH of the natural suspension. The responses of the indicators to the mineral surfaces were monitored by UV-visible spectroscopy using a scattered transmission technique. The Hammett surface acidity function (Hs) and the surface redox potential (Ehs) of these iron-bearing minerals were measured. These measured values were used to calculate Eh values for the seven minerals: goethite = +293 mV; chlorite = +290 mV; hematite = +290 mV; almandite = +282 mV; ferruginous smectite = +275 mV; pyrite = +235 mV; and Na-vermiculite = +223 mV. Calculated surface redox potentials of minerals are different from their potentials measured by platinum electrode in bulk suspensions. UV-visible spectroscopy provides a quick and non-destructive way of monitoring organic probe response at the mineral surface.

The effect of freezing and thawing on the rheological behavior of illite suspensions was studied by examining viscosity and plasticity. Stability of suspensions was characterized by a hysteresis loop of thixotropy. Thermal gravimetric and differential scanning calorimetry analysis were also used. After initial freezing and thawing, the flow curves of the suspensions show an increased viscosity, an “irregular up line”, and a greater hysteresis loop of thixotropy. The ratios of mean viscosity of previously frozen (F) and control (O) samples (ηF/ηO) for non-expandable 2:1 phyllosilicates ranges from 1.3 to 2.1. Addition of monovalent (0.1% Na2SiO3) and divalent cations (0.3% CaCl2 or BaCl2) increase and decrease the shear-stress difference between F and O samples, respectively. Prior freezing of clay samples results in an increase of plasticity by ∼20–30%. The thermal analysis data of F samples show an increase in weight loss, and a decrease in enthalpy of dehydration. The changes of physico-chemical properties from cycles of freezing and thawing are long lasting. The freezing memory effect of illite-type clays is expected to play an important role in ceramic processing, i.e., casting processes, plastic formation, and sintering.

The decomposition of kaolinite by treatment with trimethyl phosphate (TMP) and the composition of the new crystalline phase formed were studied. On hot treatment with TMP, kaolinite forms a crystalline white compound that is soluble in hot water. The X-ray diffraction pattern of the kaolinite treated shows both the typical reflections of kaolinite and, furthermore, a very strong reflection at 8.84 Å. After 30 days of treatment with TMP, the silicate structure of kaolinite is completely destroyed and a crystalline phase identical with that resulting from treatment of aluminium oxide (Al2O3) with TMP is formed. The results show that the compound in question is formed by hydrolysis of TMP, catalyzed by the hydration water of exchange cations of kaolinite, followed by removal of Al from the silicate structure by incompletely hydrolyzed TMP. The new crystalline phase thus formed is an aluminium alkyl phosphate of formula Al(CH3)6(PO4)3.

X-ray absorption spectroscopy (XAS) was used to determine the local molecular environment of Co(II) surface complexes sorbed on three different kaolinites at ambient temperature and pressure in contact with an aqueous solution. Interatomic distances and types and numbers of backscattering atoms have been derived from analysis of the extended X-ray absorption fine structure (EXAFS). These data show that, at the lowest amounts of Co uptake on kaolinite (0.20–0.32 µmol m−2), Co is surrounded by ≈6 O atoms at 2.04–2.08 Å and a small number or Al or Si atoms (N = 0.6–1.5) at two distinct distances, 2.67–2.72 Å and 3.38–3.43 Å. These results indicate that Co bonds to the kaolinite surface as octahedrally coordinated, bidentate inner-sphere mononuclear complexes at low surface coverages, confirming indirect evidence from solution studies that a fraction of sorbed Co forms strongly bound complexes on kaolinite. In addition to inner-sphere complexes identified by EXAFS spectroscopy, solution studies provide evidence for the presence of weakly bound, outer-sphere Co complexes that cannot be detected directly by EXAFS. One orientation for inner-sphere complexes indicated by XAS is bidentate bonding of Co to oxygen atoms at two Al-O-Si edge sites or an Al-O-Si and Al-OH (inner hydroxyl) edge site, i.e., corner-sharing between Co octahedra and Al and Si polyhedra. At slightly higher surface sorption densities (0.51–0.57/ µmol m−2), the presence of a small number of second-neighbor Co atoms (average NCo < 1) at 3.10–3.13 Å indicates the formation of oxy- or hydroxy-bridged, multinuclear surface complexes in addition to mononuclear complexes. At these surface coverages, Co-Co and Co-Al/Si distances derived from EXAFS are consistent with edge-sharing between Co and Al octahedra on either edges or (001) faces of the aluminol sheet in kaolinite. Multinuclear complexes form on kaolinite at low surface sorption densities equivalent to <5% coverage by a monolayer of oxygen-ligated Co octahedra over the N2-BET surface area. These spectroscopic results have several implications for macroscopic modeling of metal ion uptake on kaolinite: 1) Primary binding sites on the kaolinite surface at low uptake are edge, non-bridging Al-OH inner hydroxyl sites and edge Al-O-Si bridging oxygen sites, not Si-OH sites typically assumed in sorption models; 2) specific adsorption of Co is via bidentate, inner-sphere complexation; and 3) at slightly higher uptake but still a small fraction of monolayer coverage, formation of Co multinuclear complexes, primarily edge-sharing with Al-OH octahedra, begins to dominate sorption.

In the Tertiary lacustrine sediments of the Jbel Rhassoul (Morocco), stevensite and sepiolite, confined to the dolomitic facies, are commonly mixed at lower parts of the so-called “Formation Intermédiaire”. Transmission electron microscopy (TEM) observations reveal a relation between these 2 magnesian clay minerals. One can observe the different transition steps, from the initial folded layers of stevensite to the fibers emerging from the layers, and finally to the complete replacement of stevensite by sepiolite. That transition can also be observed by scanning electron microscopy (SEM), where the fibers seem to grow at the expense of stevensite. Thermodynamic calculations have been applied to provide geochemical conditions for the formation of sepiolite after stevensite. Early deposition of the “Formation Intermédiaire” occurred under climatic conditions varying between dry and wet. During dry periods, the relative silica enrichment and the pH decrease in the lake water should destabilize stevensite, leading to the formation of sepiolite. Subsequently, a perennial wet climate would lead to the formation of pure stevensite without any trace of sepiolite.

The crystal structure of single crystals of kaolinite from Keokuk, Iowa, was refined using data measured at the microfocus X-ray beamline at the ESRF, Grenoble, France (λ = 0.6883, T = room temperature). The volume of the crystals was 8 and 0.8 μm3, respectively. Unit-cell parameters are: a = 5.154(9) Å, b = 8.942(4) Å, c = 7.401(10) Å, α = 91.69(9)°, β = 104.61(5)°, γ = 89.82(4)°. Space group Cl is consistent with the observed data. All non-hydrogen atoms were independently refined with anisotropic displacement parameters. The positions and isotropic displacement parameters for the three interlayer H atoms were refined also. The position of the intralayer H was found by difference-Fourier methods, although refinement was not possible. Difference-Fourier maps suggested large anisotropic displacement vectors of this intralayer H, however, no evidence for a second maximum was found. The diffraction patterns show diffuse scattering in streaks parallel to [001]* through hkl reflections with hk ≠ 0, which is caused by stacking faults. No twinning was observed for either of the two crystals.

One Tertiary and two Cretaceous gray kaolin sites in Georgia were examined using X-ray radiography of core sections to determine the processes of formation of the deposits. The Tertiary kaolin was oxidized in the upper 3 m of the deposit and reduced below that point. The two Cretaceous kaolins were reduced from the top of the deposit to an abrupt boundary with oxidized red kaolin below. Radiography of the first Cretaceous core revealed thin laminar bedding in the gray kaolin and in the underlying red kaolin. The laminae continue without interruption across the gray kaolin/red kaolin boundary. The laminae were not visible in the gray kaolin except in radiographs. Sedimentary bedding was not observed visually or radiographically at the Tertiary site nor in sections of the core from the second Cretaceous site where kaolinite was recrystallized to large vermiforms. The original sedimentary structure in the first Cretaceous kaolin was preserved possibly due to the inhibition of kaolinite recrystallization by a higher organic matter content. Recrystallization of kaolinite and iron compounds may have destroyed sedimentary structures in part or all of the other two kaolin cores. It is hypothesized that the first Cretaceous physical and biological mixing. The same hypothesis may apply to the other two kaolins but recrystallization after deposition has destroyed sedimentary structures.

Electrophoretic mobility of imogolite has been reported as positive (migration toward the negative electrode) below pH 9, and zero above pH 9. However, when mobility of dilute imogolite suspensions (5 × 10−3 kg/m3) was measured, it was found to be negative above pH 9. The reason that imogolite does not behave as a negative colloid when the clay concentration is not very dilute is because the imogolite forms floccules large enough to prevent migration. Imogolite has a PZNC at about pH 6, and has a PZC at pH 8.5–9.0 showing a relatively low absolute mobility under alkaline conditions compared to that under acid conditions. The fact that imogolite behaves like this is understandable given the location of negative charge appearing on the inside surface of the thin fibrous tube, according to the structural model of imogolite.

Variation of the NH4+-exchange and CO2-adsorption capacities with zeolite content was investigated in detail to assess the potential use of these capacities for the estimation of the zeolite contents of the samples taken from the Bigadiç clinoptilolite deposit in western Anatolia, as an alternative to the widely used semi-quantitative X-ray diffraction (XRD) technique. Samples with known clinoptilolite contents taken from 2 different zones with fine- and coarse-grained tuffs of the Bigadiç deposit were used for this purpose. Na-enriched forms of the samples were prepared by repeated ion-exchange with NaCl solutions, and NH4+-forms by repeated Na exchange followed by NH4+ exchange with NH4Cl solutions, which in turn were calcined to obtain the H-forms. NH4+-exchange capacities by Kjeldahl analyses of the NH4+-forms and CO2 adsorption isotherms in the 0 to 100 kPa range of Na- and H-forms of the samples were determined. Dubinin-Astakhov model parameters were calculated from the isotherm data.

A strong relationship exists between the experimental CO2-adsorption capacities at 100 kPa of the Na-forms and the zeolite contents of the samples. Although the Dubinin-Astakhov model represented the isotherm data quite well, the relationships between the amounts of adsorbate at saturation pressure, calculated from the model, and the zeolite contents of the samples were weaker. The strength of the relationship between NH4+ exchange capacities and zeolite contents was seen to vary with the zone of origin. There is a very strong relationship between the adsorption and ion-exchange capacities of the samples in their Na-forms taken from the fine-grained zone, indicating that either ion-exchange or adsorption capacity measurements can be used to estimate the zeolite contents of the samples taken from this zone, whereas, significant diffusion hindrance was observed against ion-exchange of hydrated cations from aqueous solutions for some samples from the coarse-grained zone. Inspection of the data pointed to systematic errors in the zeolite contents determined by a semi-quantitative XRD technique. When both zones are considered together, CO2-adsorption capacities at 100 kPa of the samples in their Na-forms can be used as a reliable measure of the zeolite content, which in turn is an important index to predict the performance of natural samples in various applications.

The interactions of the following three kinds of racemic and enantiomeric cobalt(III) chelates with montmorillonite and saponite are studied: [Co(en)3]3+ (en = ethylenediamine), [Co(diNOsar)]3+ (diNOsar = (1,8-dinitro-3,6,10,13,16,19-hexaazabicyclo[6,6,6]-eicosane)cobalt(III))and [Co(diAMsar)]3+ (diAMsar = (1,8-diamino-3,6,10,13,16,19-hexaazabicyclo-[6,6,6]eicosane)-cobalt(III)). At neutral pH, these complexes are adsorbed as a trivalent cation up to 90%–100% of the cation exchange capacity of a clay. No difference is observed in the maximum adsorption amount between the racemic and enantiomeric isomers. The basal spacings of the clay-chelate adducts are determined by the X-ray diffraction measurements of non-oriented powder samples: 14.3 Å for [Co(en)3]3+ montmorillonite, 16.5 Å for [Co(diNOsar)]3+ montmorillonite, and 16.9 Å for [Co(diAMsar)]3+ montmorillonite. The results imply that the chelates form a monolayer in the interlayer space. From the one-dimensional Fourier analyses of the diffraction pattern of [Co(diNOsar)]3+ montmorillonite, the chelate is concluded to be adsorbed with its three-fold symmetry axis in parallel with the layer surface. This is in contrast with the previous results of [Ru(phen)3]2+ and [Ru(bpy)3]2+, which are adsorbed with their three-fold symmetry axes perpendicular to the surface. The conclusion is consistent with the angular dependence of the infrared absorption spectrum of the film of the adduct.

The effect of heat treatments on the swelling, dispersion, particle charge and particle aggregation of Li-, Na-, K-, Mg-, Ca- and Al-Wyoming bentonite was investigated. Before thermal treatment, unheated (25 °C) Li-, Na- and K-clays showed increased d001 spacing on glycerol solvation and dispersed spontaneously in water. Mg-, Ca- and Al-clays did not disperse spontaneously in water, but the d001 spacing increased upon glycerol solvation. After heating at 300 °C or above, none of these clays dispersed spontaneously. However, swelling varied with the type of cation and the temperature of heating.

The results generally suggested that swelling and dispersion of homoionic Wyoming bentonite after heating at various temperatures depended upon the nature of bonding between clay particles and the cations. Enhanced swelling and dispersion of clays indicated the more ionic character of the cationic bonding than cases where heating resulted only in swelling, with polar covalent bonding of cations to clay surfaces allowing limited hydration. It is also suggested that, when both swelling and dispersion as a result of thermal treatment are absent, a covalent bond is formed between cation and clay surface.

Thermal treatment apparently affects the bonding in different ways. It appears that the smaller cations (ionic radius <0.7 Å) Li, Mg and Al migrate to octahedral vacant sites and form covalent bonds after heating at 400 °C; this drastically reduces the negative charge. This process for Li-clays occurred even at 200 °C. The larger cations (ionic radius > 0.9 Å) Na, K and Ca apparently did not migrate into the lattice sites after heating to 400 °C; a high proportion of them were exchangeable. The data for exchangeable cation, particle charge and clay particle size were consistent with the postulated effect of the nature of cationic bonding upon swelling and dispersion properties.

The objective of this study was to investigate the influence of layer charge on the hydration of Mg-saturated expandable 2:1 phyllosilicates. Water retained by 12 Mg-saturated clays at 54% relative humidity was quantified gravimetrically. X-ray diffraction and total chemical analysis were used to determine the hydratable surface area (447–759 m2 g−1) and layer charge [0.327–0.754 electrons per formula unit (e f.u.−1)] of each sample. Water retained by the clays increased with both hydratable surface area and layer charge of the clays. However, the increase in H2O content with layer charge occurred only on external surfaces of the clays. This result suggests that the H2O on external surfaces is localized around the cation/charge sites rather than forming multi-layers as was suggested previously. A model is proposed for the hydration of expandable 2:1 phyllosilicates. The model assumes that interlayer volume controls interlayer hydration and that the number of cation/charge sites on external surfaces controls hydration of external surfaces.

Nonexchangeable polymers in interlayers of expansible phyllosilicates influence thermal dehydration in ways not completely understood. Thermal dehydration of hydroxy-interlayered vermiculite (HIV) from Florida soils, for example, results in irreversible d001 shifts. This study was conducted to characterize HIV dehydration as a function of time (t) and temperature (T), and to determine how reversibility of dehydration is affected by elevated T. Clay-sized HIV from 3 soils was heated incrementally and d-spacing shifts (Δd) were monitored by X-ray diffraction (XRD) at low relative humidity (RH). Samples were then mounted on a metal heating strip in the XRD focal plane and scanned repeatedly at constant T levels to monitor Δd with t. Finally, Δd in response to RH shifts from <5% to >85% was determined at 25°C and at elevated temperatures. Incremental heating revealed a Δd plateau roughly corresponding to the z dimension of hexameric octahedrally coordinated Al. The initial slope of Δd-vs-t curves increased with T. The same maximum Δd reached at 200°C was reached at 160°C, but more slowly. All samples exhibited reversible and irreversible dehydration, the former being attributable to sites in equilibrium with external vapor and the latter to sites requiring heat for desorption. Reversible sites were not perturbed by moderate heating, but were apparently eliminated by polymer dehydroxytation. The dehydration behavior of HIV could be explained by steric resistance of water vapor diffusion within a tortuous interlayer polymeric network. Alternatively, new polymer/oxygen-surface bonds exceeding the hydration energy of interlayer components could form via heat-induced re-articulation of polymer/oxygen-surface bonds at smaller basal spacings.

Thermal analysis involves a dynamic phenomenological approach to the study of materials by observing the response of these materials to a change in temperature. This approach differs fundamentally from static methods of analysis, such as structural or chemical analyses, which rely on direct observations of a basic property of material (e.g. crystal structure or chemical composition) at a well-defined set of conditions (e.g. temperature, pressure, humidity). Clay minerals are highly susceptible to significant compositional changes in response to subtle changes in conditions. For example, changes in the fugacity of water affect the stability of interlayer H2O in a clay mineral (see below). Therefore, care must be taken that all experimental conditions are known with accuracy and precision

Nacrite, dickite and intermediate dickite-nacrite phases have been identified from the upper Paleozoic sequences of the Maláguide Complex (Betic Cordilleras, Spain). Nacrite developed as euhedral, pseudohexagonal or elongated crystals within sandstones and thin, irregular veins. Dickite developed preferently within extensive zones of fractures as very irregular, compact packets. Intermediate phases occurred in the sandstones and veins similar to the nacrite, or accompanying dickite. The mineral assemblage of the sandstones includes quartz-muscovite-kaolinite-type minerals, with or without albite, carbonates, chlorite and mixed-layers containing chlorite. The metamorphic conditions in which these minerals formed belong to anchizone, as can be deduced from the IC values. Dickite, nacrite and intermediate phases were studied by X-ray diffraction, infrared spectroscopy, differential thermal analysis and micros-copy. The results for dickite indicate a well-ordered mineral and agree with most of the published data. Conversely, IR spectra and DTA curves of nacrite show some differences in relation to the available data for this mineral. Based on the comparison with dickite and nacrite data, intermediate phases can be interpreted either as disordered varieties or as mixed-layered dickite/nacrite.

Otay-type waxy bentonites of San Diego County are illite-smectite (I-S) with 85% dioctahedral smectite mixed with dioctahedral illite showing a Reichweite of 0. Primary or secondary waxy bentonite exposures are found in all Eocene and Oligocene formations of southwest San Diego County and western Baja California north of Ensenada. Primary waxy bentonites formed when hot volcanic ash fell into quiet marine or brackish coastal water. The transformation from glass to bentonite occurred within hours or days but consolidation of the bentonite into its waxy consistency took longer. Primary waxy bentonite consists of 95 wt% I-S with the remainder consisting of volcanic glass shards, sanidine fourling twins, hexagonal biotite crystals and amorphous manganese oxides and hydroxides. Secondary waxy bentonite is primary waxy bentonite that was mixed with nonvolcanic detritus either before consolidation or after consolidation and subsequent erosion. The hydrophobic character of primary waxy bentonite allows it to reflect, accurately, the chemistry and petrology of the original volcanic material. Chemical analysis of primary waxy bentonites shows that the original lava was subduction-related and exhibited petrologic variations nearly identical to those of the modern Cascades of the northern Pacific coast of the lower United States. Primary and secondary waxy bentonites as well as smectites derived from the weathering of volcanic ash that fell outside the waxy bentonite-producing environments are the previously unrecognized products of extensive Eocene and Oligocene subduction-related volcanic activity. Baja California exposures of waxy bentonite demonstrate pre-Pliocene subduction tectonics that gave way to rifting tectonics.

Experiments on zeolitization were conducted on four synthetic monocationic glasses (Na, K, Ca, or Mg-rich glass) with Si/Al molar ratios of 2.67, similar in acidity to many volcanic glasses of partially zeolitized Italian tuffs. The products of the hydrothermal treatment at 100, 150, and 200°C of single glasses or glass mixtures with deionized H2O or monosaline solutions (NaCl, KCl, CaCl2) were characterized by X-ray diffraction, thermal, microscopic and chemical analyses. Chemical analyses of mother liquors were also performed. Mineral assemblages, containing chabazite, phillipsite, analcime, and K-feldspar, very similar to those found in altered, volcaniclastic alkali-trachytic or trachytic glass deposits were produced. Potassium was essential to chabazite and phillipsite crystallization, although phillipsite was obtained also in Ca-Na mixed systems. Sodium was necessary for analcime formation. Calcium plays only a secondary role in zeolitization, and magnesium does not favor zeolite crystallization but promotes the formation of smectite. Glass composition determines the mineral assemblages obtained and hence in those commonly found in nature.