The K-Ar systematics of illite/smectite (I/S) mixed layers in deeply buried shales from the Gulf Coast, the North Sea and the Mahakam Delta basins have been compared to provide additional perspectives on the diagenetic evolution of these minerals. Comparison of the results suggests that illitization proceeds similarly in the 3 basins, at least for the increase in the illite-layer and K contents, despite differences in the provenance of the detrital components, the ages of deposition, the depths of burial and the tectonic history of the basins. Analysis of the trends with depth in the illite-layer and K contents of I/S-enriched size fractions of shales in the North Sea and the Mahakam Delta basins shows that these trends represent segments of the more complete trends from I/S minerals of the Gulf Coast area.

The trends with depth in the radiogenic 40Ar contents and in the K-Ar ages of the I/S-rich fractions in the North Sea and Mahakam Delta basins suggest that, relative to the reference trends of the Gulf Coast area, the K-Ar system of the clay material is more dependent on the behavior of the radiogenic 40Ar than on the occurrence or non-occurrence of detrital grains in the size fractions. Recasting of the available data suggests that retention of radiogenic 40Ar by the illite-type minerals occurs in the intense illitization zone and release occurs in the deeper part of the basins. We therefore speculate that the illitization process of the I/S mixed layers of progressively buried shale-type sediments could be controlled by a transformation process integrating dissolution of detrital components in poral rock environments relatively impermeable to radiogenic 40Ar. These excesses, which might be partly or completely erased in deeper parts of the sedimentary basins, question the application of the K-Ar dating method on clay minerals extracted from shales.

The chemical composition of mixed-layer serpentine/chlorite (Sp/Ch) in Tuscaloosa Formation sandstone was analyzed by energy dispersive X-ray spectroscopy (EDX) in the scanning electron miscroscope (SEM) and by X-ray diffraction (XRD). EDX results indicate little depth-controlled variation in composition, whereas XRD results suggest distinct decreases in octahedral Fe and tetrahedral Al. XRD-determined compositions appear to be erroneous and actually reflect progressive changes in Sp/Ch unit-cell dimensions caused by polytype transformations of Ibb layers to Iaa layers in a mixed-layer Ibb/Iaa polytype. The relative lack of variation in Sp/Ch composition, especially when compared to other studies of chlorite minerals over similar temperature ranges, is attributed to a reaction mechanism whereby mineralogic transformations (serpentine layers to chlorite layers and Ibb layers to Iaa layers) occur on a layer-by-layer basis within coherent crystallites, rather than by dissolution-precipitation crystal growth.

The lack of titanium in chlorite minerals is attributed to high levels of octahedral Al3+ that prohibit inclusion of the highly charged Ti4+ in the octahedral sheet. Anatase (TiO2) in the Tuscaloosa Formation apparently formed when Ti was liberated during crystallization of Sp/Ch following the breakdown of a Ti-bearing precursor (detrital ultramafic clasts and/or odinite). Odinite, an Fe-rich 7-Å phyllosilicate that forms in some shallow marine sands, apparently existed as a short-lived, poorly crystallized intermediary between dissolution of the ultramafic clasts and formation of Sp/Ch.

An Fe-berthierine occurs in a buried laterite from the Late Cretaceous (Cenomanian) in southwestern Minnesota. It formed beneath a lignitic horizon in which reducing solutions percolated through a laterite comprising gibbsite, kaolinite and goethite. Morphologic differences suggest 2 separate conditions of Fe-berthierine formation. Early forms of Fe-berthierine include radial bladed or radial blocky crystallites coating pisoids, along with alteration of kaolinite at crystal boundaries. These morphologies formed in the vadose zone. Later forms precipitated under subaqueous conditions as macroscopic, pore-filling cement. The large size of the later-formed Fe-berthierines enabled microprobe characterization. This 1st reported occurrence of Mg-free berthierine has a structural formula close to an idealized Fe-berthierine: Fe2Al2SiO5(OH)4. Apart from their chemistry, the unique feature of the Minnesota Fe-berthierines is their formation in an exclusive nonmarine depositional environment. They formed in situ as part of a lateritic weathering profile developed on a broad, low relief peneplain. Physical evidence of formation under nonmarine conditions includes the presence of 1) scattered lignitic fragments; 2) concretions forming casts and molds of woody material; and 3) a nonmarine fossil (Unio sp. undet). Chemical evidence includes siderites collected from the berthierine-bearing horizon having stable isotope values indicating freshwater formation.

Vermicular glaucony grains observed by transmission electron microscopy (TEM) show three irregularly alternating zones. Zone A has a high degree of linear orientation, no void space, and relatively defect-free lattice-fringe images. Zone B has an amalgamated bundle texture with a sub-parallel, linear orientation of bundles to each other and to zone A. Zone B has little or no void space, and lattice images appear to be a combination of those typical of zone C with minor amounts of modified zone A forms. Zone C has a randomly oriented, curved, and circular or semicircular bundle texture. In addition, zone C has much void space and curvilinear and linear lattice-fringe images with numerous defects, including edge dislocations. Such morphologic and crystallographic characteristics indicate that zones B and C probably comprise the glauconitic minerals of the vermicular glaucony grains, and that zone A comprises non-glauconitic micaceous minerals of higher structural order. Zone B is sharply demarcated from zone A, but B zone bundle textures merge gradationally to those of zone C. These spatial relationships suggest that zone B forms first on the surface of zone A. Sub-parallel orientation in the B zone could be produced by initial confinement between adjacent A zones. Once constraints change or are removed, the randomly oriented, curved, and semicircular or circular bundles of zone C develop.

The sedimentation behavior of a fine kaolinite, comprising a substantial proportion of colloidal particles as well as non-colloidal ones, has been studied when fresh FeCl3 or F2(SO4)3 electrolytes are added. The sedimentation behavior depends on the pH and the nature of electrolytes and can be explained qualitatively, in our study, by the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO theory). Fe helps also to aggregate the kaolinite particles in flocs. Two extreme kinds of qualitative sedimentation have been observed: flocculation-sedimentation and accumulation-sedimentation. However, the transition between the two kinds of sedimentation is quite progressive. The present results are discussed in reference to the DLVO theory and the hydrolysis behavior of Fe electrolytes.

The colloidal state (stable, coagulated, or gel-like) and the rheological properties of Na-rich montmorillonite (Wyoming) dispersions are strongly influenced by organic cations. This effect is shown for homologous organic cations: alkyl trimethylammonium ions, paraquat, diquat, alkyl bispyridinium ions, and the triphenylmethane dyes crystal violet, methyl green, and tris (tri-methylammonium phenyl) methane chloride. The critical coagulation concentrations, cK, are small (often < 1 mmol/L) because the cations are enriched in the Stern layer and influence the solvent structure near the surface. The strong adsorption of the counterions at the clay-mineral surface causes cK values to increase with the solid content. Charge reversal (recharging) of the particles was observed with the longer chain alkyl trimethyl-ammonium ions, dodecyl bispyridinium ions, and crystal violet. Other cations reduced the electrophoretic mobility to zero but positive particle charges were not observed.

The plastic viscosity increased sharply at the critical coagulation concentration and showed a minimum slightly below cK, which was caused by the electroviscous effect. Yield values were developed at concentrations above cK. In most cases, yield values reached a plateau where the amount of organic cations was ∼0.5 mmol/g, i.e., about half of the cation-exchange capacity. The cK values decreased with increasing hydrophobicity of homologous compounds, but the yield value showed maxima at intermediate chain lengths. The yield value of several 0.5% dispersions was high, e.g., dodecyl trimethylammonium ions, 71 Pa; paraquat, 100 Pa; diquat, 42 Pa; hexyl bispyridinium ions, 53 Pa (vs. Ca2+, 0.2 Pa; Al3+, 0.7 Pa). The storage modulus as a function of the number of organic cations changed in a similar way as the yield value, and high values were observed (e.g., dodecyl trimethylammonium ions, hexyl bispyridinium ions: 1000 Pa, paraquat: >4000 Pa). Thus, dispersions with high viscosity, yield value, and pronounced viscoelasticity are obtained by coagulating Na-rich montmorillonite dispersions with organic cations.

Solutions containing hydroxy-FeAl oligocations (HFA) were prepared by two procedures: (1) treatment of a mixture of FeCl3 and AlCl3 with aqueous Na2CO3, followed by aging of the product and (2) preliminary preparation and aging of hydroxy-Al13 oligocations followed by reaction of the latter with aqueous FeCl3. Ion-exchange of Na-montmorillonite with HFA yield pillared clay (designated as FeAl-PILC) with d(001) values of 1.98–1.56 nm and a surface area of 230 m2/g. The pillar structure, thermal stability, surface acidity, and reduction behavior of the pillared clays were determined by 27Al-NMR, XRD, DTA, Mössbauer spectroscopy, Py-IR, TPD, TPR. Fe/Al ratios greatly affect the pillar structure, surface area and thermal stability of FeAl-PILC. The pillar in FeAl-PILC with Fe/Al ratio <0.5 has a Keggin structure, similar to that of Al-PILC, but the pillar structures of FeAl-PILC with Fe/Al ≥0.5 are the ferric tripolymer species similar to those of Fe-PILC. The basal spacings, surface area, and thermal stability are decreased with increasing Fe/Al ratio. There is relatively strong interaction between Fe and Al in the pillars. The interaction is enhanced with decreasing Fe/Al ratio. Reduction of the Fe phase in FeAl-PILC was reduced by the interaction of Fe with Al.

X-ray diffraction of four natural samples of ferrihydrite indicates the presence of crystalline domains within the primary particles. The average diameter of the primary particles (determined from low-angle powder patterns) decreases from 4.1 nm to 2.5 nm as the domain size in the xy-plane (determined by applying the Scherrer equation to the broad [110] XRD peak at 0.26–0.27 nm) decreases from 1.0 nm to 0.77 nm. The Si content (measured by acid-oxalate extraction) increases from 4.1% to 6.1% as both the domain and particle sizes decrease; other factors, however, are likely to be important in influencing particle size. For one sample of ferrihydrite, the smallest possible domain (i.e., c = 0.94 nm in the z-direction) contains 36 O atoms and three Si atoms. A model for ferrihydrite is suggested in which silicate bonds to, and bridges, the surfaces of the domains. The model can account for several aspects of the behavior of siliceous ferrihydrites.

The influence of surfactants on the flow behavior of sodium montmorillonite dispersions (2% w/w) was studied for a cationic (cetylpyridinium chloride, CPCl) and an anionic surfactant (sodium dodecylsulfate, SDS). When the dispersion pHs were >3.5 and <7, CPCl concentrations >10−4 M increased the shear stress but the Bingham yield value remained virtually unchanged (τo ≈ 100 mPa). At pH ≈ 7, the shear stress and yield point decreased with increasing CPCl concentration (τo from 430 to 100 mPa). The flow properties of sodium calcium bentonite dispersions were independent of pH and CPCl concentrations ≤ 10−4 M; they increased modestly at higher concentrations. At pH < 4, SDS addition to the sodium montmorillonite dispersions increased the shear stress and yield value to a maximum value (τo = 2100 mPa) at 10−3 M SDS; higher SDS concentrations reduced the shear stress and yield value. At pH > 4, the flow values decreased to a minimum value at 10−2 M SDS (τo from 430 to 50 mPa). The flow of the sodium calcium bentonite dispersions at pH > 4 was independent of SDS concentrations ≤ 10−3 mole/liter; at higher SDS concentrations, the flow values increased more strongly in sodium calcium bentonite than in sodium montmorillonite dispersions.

Surfactants influence the flow behavior of sodium montmorillonite dispersions by their action on the card-house networks in strongly acidic medium and, at higher pH, by the electroviscous effect. At the highest surfactant concentrations without flocculation, the shear stress and yield value are increased by interacting chains of opposed particles.

Addition of the surfactants increases the salt (NaCl) stability of the dispersions because the adsorbed surface active agents influence the counterion distribution between the Stern and the diffuse ionic layer.

Highly tectonized contact between serpentinite and younger pegmatite in the magnesite mine of Wiry contains various layer silicates. Vermiculite, chlorite, smectite, and interstratified mica-vermiculite were recognized by means of routine XRD examination. Two three component interstratifications of mica-vermiculite-chlorite and chlorite-swelling chlorite-smectite were identified by a combined procedure of deconvolution of the XRD patterns and simulation of XRD tracings. A mineral with large diffraction maxima, displaying “chlorite intergrade” characteristics, appeared to be a mixture of chlorite, mixed layer chlorite-smectite, and vermiculite. Polytypes of phyllosilicates were determined by the X-ray transmission method. Due to the heritage of parent mineral polytype structure by transitional products of alteration, two distinct sequences of layer silicates were observed: one formed from trioctahedral mica (vermiculite, mixed layer mica-vermiculite); and one evolved from chlorite (e.g., mixed layer chlorite-swelling chloritesmectite). A tentative scheme of the primary contact zone structure, not obscured by subsequent brittle tectonics either by transformation of layer silicates, is proposed.

NEXAFS is shown to be an excellent technique, of potentially widespread application, for the determination of the orientation of organic molecules intercalated in preferentially oriented thin films of polycrystalline, layered minerals. A NEXAFS study of [Mg2Al(OH)6]+C7H5O2 · nH2O, a layered anionic clay, is described. This material shows a transition from a layer spacing of 15.4 Å to only 9 Å at a remarkably low temperature (below 100°C). This is shown to be accompanied by a change in the angle of the plane of the benzoate molecule to the 00ℓ planes from 35° ± 10° to 0° ± 10°. The tilt of the benzoate anion in the room temperature structure demonstrates the presence of an interaction between the phenyl ring and the positively charged, brucite-like layers. Furthermore it is suggestive of the importance of hydrogen bonding in determining the interlayer spacing and stability.

Chlorite minerals, found in a great variety of rocks and geological environments, display a wide range of chemical compositions and a variety of polytypes, which reflect the physicochemical conditions under which they formed. Of particular importance for studies dealing with ore deposit genesis, metamorphism, hydrothermal alteration or diagenesis is the paleotemperature of chlorite crystallization. However, in order to understand the relationship between chlorite composition and formation temperature and hence use chlorite as a geothermometer, one must determine how other parameters influence chlorite composition. These parameters may include fO2 and pH of the solution and Fe/(Fe + Mg) and bulk mineral composition of the host rock.

Four approaches to chlorite geothermometry, one structural and three compositional, have been proposed in the past: 1) a polytype method based on the (largely qualitative) observation that structural changes in chlorite may be partly temperature-dependent (Hayes, 1970); 2) an empirical calibration between the tetrahedral aluminum occupancy in chlorites and measured temperature in geothermal systems (Cathelineau, 1988), which has subsequently been modified by several workers; 3) a six-component chlorite solid solution model based upon equilibrium between chlorite and an aqueous solution, which uses thermodynamic properties calibrated with data from geothermal and hydrothermal systems (Walshe, 1986); and 4) a theoretical method based on the intersection of chlorite-carbonate reactions and the CO2-H2O miscibility surface in temperature-XCO2 space, which requires that the composition of a coexisting carbonate phase (dolomite, ankerite, Fe-calcite or siderite) be known or estimated (Hutcheon, 1990). These four approaches are reviewed and the different calculation methods for the compositional geothermometers are applied to a selection of chlorite analyses from the literature. Results of this comparative exercise indicate that no single chlorite geothermometer performs satisfactorily over the whole range of natural conditions (different temperatures, coexisting assemblages, Fe/(Fe + Mg), fO2, etc.). Therefore, chlorite geothermometry should be used with caution and only in combination with alternative methods of estimating paleotemperatures.

Clay mineral compositions from 2 paleosol profiles (Chu-Wan, CW, and Shiao-Men Yu, SMY, profiles) on the late-Miocene sediments in Penghu Islands (Pescadores), Taiwan, are characterized by random X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). By the clay assemblage of the paleosol profile, we want to explore the probable formation mode of the Penghu paleosols.

The paleosol profiles in study are overlain by a layer of basalt flow. However, the clay mineralogy of the 2 paleosols was not altered metasomatically after burial. Results show that 3 distinctive zones of different dominating kaolin-group minerals are apparent in the profiles. In descending order, they are: 1) spheroidal, hollow 7Å-halloysite, 2) platy, irregular-shaped and disordered kaolinite, and 3) platy, irregular-shaped, disordered kaolinite. The relative crystallinity of kaolin minerals of the 3 layers is: layer 2 > layer 3 > layer 1. On the basis of the XRD, TEM analyses and the crystallinity calculations, the distribution of kaolin in Penghu paleosol profiles appears to be unique. Penghu paleosol profiles show systematic change in kaolin crystallinity and polymorphs with depth. Because the clay type is heterogeneous within the profile, this represents that Penghu paleosol profiles were polypedogenic.

The contact between the upper basalt and the paleosol is the erosion surface, so we do not know exactly what the thickness of the original paleosol was. The first layer (about 20 cm) of the profiles appears to be constituents of the original paleosol. It contains high contents of pedogenic (in situ weathering) hematites and 7Å-halloysites, which implies that the local climate of the Penghu Islands at late Miocene was warm and humid. Intense leaching and dry/wet cycle should be the reason for high contents of halloysite (>60%) in the Penghu paleosols. Laterization was the probable pedogenic process for the formation of the paleosols.

Saponite, hectorite, and laponite have been pillared with cationic Al clusters, and special attention has been given to the solution chemistry or Al. Pillared saponite is obtained after exchange with refluxed Al solutions; while for hectorite, Al solutions treated with ammonium acetate give a pillared product with 1.8–1.9 nm spacing and thermal stability up to 873 K. In both types of solutions, the Keggin ion Al cluster is a minority species or totally absent. The typical 1.8–1.9 nm spacing is only obtained after washing. The quality of the pillared material can be judged from its thermal stability, its surface area, and the width of the d001 line before and after pillaring. The width should not exceed 0.3 nm before calcination and 0.5 nm after calcination. The latter criterion reflects the importance of the crystallinity of the parent clay for successful pillaring. Pillaring in concentrated conditions occurs by a combination of ion exchange and precipitation of Al and gives materials that exhibit poor thermal stability.

A kaolin clay occurring in Carboniferous mudstone near the Jiangshan-Shaoxing deep fault in Zhejiang Province, eastern China was characterized by XRD and IR. Although the dominant mineral appeared to be kaolinite, IR also suggested the possible occurrence of nacrite. This was confirmed by forming intercalation complexes with potassium acetate and with hydrazine hydrate, both water complexes having the same characteristic spacing at 8.35 Â. Different particle size fractions of the kaolin clay were studied and the results indicated that nacrite content increased with increasing particle size. This occurrence of nacrite is consistent with previous findings of the polytype in high temperature and pressure environments.

A swelling mica, Na2Mg3(Al2Si2)O10F2·xH2O, (hereafter “Na-4 mica”) was synthesized from metakaolinite + MgO and Mg aluminosilicate gels at different temperatures and durations using NaF flux. The various samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and 27A1 and 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The results showed that phase-pure Na-4 mica was obtained from metakaolinite which serves as a cost-effective aluminosilicate source. 27Al MAS NMR spectra showed that all or nearly all Al is in tetrahedral coordination whereas 29Si MAS NMR spectra showed that the nearest neighbor environment of Si is mainly Si(3Al), as expected based on the Si:Al ratio.

Hydroxyaluminosilicate (HAS) ions prepared from hydroxy-Al (HyA) ions and orthosilicic acid at different NaOH/Al molar and Si/Al atomic ratios were fixed in the interlayer spaces of vermiculite (Vt). The electric charge and surface characteristics of HAS-Vt and HyA-Vt complexes formed were investigated in the pH range of 4 to 8. At pH 4 to 6, the magnitude of negative charge (CEC) of HAS-Vt and HyA-Vt complexes was drastically reduced by a HAS- or HyA-interlayer formation of Vt. At pH 7 to 8, especially in NaOH/Al molar ratio of 2.5, the magnitude of negative charge was from 62 to 89% of CEC in untreated Vt, suggesting that part of HAS or HyA ions fixed on Vt was excluded from its interlayer spaces. The positive charge did not develop on HAS-Vt and HyA-Vt complexes at pH between 4 and 8. The fixation of HAS or HyA ions on Vt caused the significant reduction of its total and internal surface areas as well as the slight increase of its external surface area. The HAS- or HyA-fixation in the interlayer spaces of Vt was confirmed by X-ray diffraction analysis. Our results provided evidence of a possibility that Vt could fix HAS ions in the same way as HyA ions, transforming to chloritized-Vt. These interlayer materials could play a significant role in modifying the surface and mineralogical properties and cation exchange capacity of clays and soils.