The crystal structure of amesite-2H1 from the Postmasburg Mn ores of South Africa has been refined to R = 4.7% using Siemens P4 rotating-anode MoKα X-ray data and SHELXL-93 software. Partial ordering of tetrahedral Si,Al and especially of octahedral Mg,Al has reduced the ideal P63cm symmetry to triclinic P1 (refined as C1). Tetrahedral rotation of 15° moves the basal oxygens toward the octahedral cations in the same layer but away from the OH H-donors of the next layers. The ordering pattern of AlIV and AlVI is unique in that the locus of Al-rich sites consists of 2 intersecting sets of zigzag lines parallel to X2 and X3, plus 2 Al-rich octahedra in layer 2 instead of the usual 1 site.

Three authigenic muscovite morphologies are associated with Norphlet Formation stylolitization observed in the Texaco Mobile Area Block 872 #1 well: l)large crystals of 1M muscovite, which grew in the stylolites with their c-axes parallel to the plane of maximum compressive stress; 2) fine-grained bundles of muscovite that occur as pore-fillings near stylolites; and 3) pods of fine-grained muscovite that exist within stylolite insoluble residue and that were precipitated as pore-filling muscovite before the host sandstone pressolved.

The population of large crystals of 1M muscovite grew at 51 ± 9 Ma, pore-filling muscovites precipitated at 77 ± 22 Ma, and muscovite pods have ages of 86 ± 16 Ma, as indicated by 40Ar/39Ar laser fusion. Apparent ages indicate that stylolitization was coincident with the beginning of organic maturation Zone 5 and could be the product of reservoir fluid pressure fluctuations induced by gas leakage. The lower Smackover Formation source/seal rock, acting as a pressure relief valve, could have been compromised by microfractures occurring during hydrocarbon generation and expulsion. Decreases in reservoir fluid pressure would have acted upon the sandstone framework by increasing the effective overburden pressure, thus making the rock more susceptible to pressure solution.

Stylolite frequency and quartz cement volume increase in the finer grained portion of the conventional core. Quartz cement volume correlates inversely to percent sandstone porosity. Apparent muscovite ages indicate that stylolitization occurred after hydrocarbon migration. Silica mobility was limited because pressure solution mineral products were precipitated from within grain films of irreducible water within the sandstone.

Stylolitization of quartz grains accounts for a minimum of 34% of the quartz cement in the upper cored section of the Norphlet Formation and minimum of 17% of the quartz cement in the lower cored Norphlet Formation. Quartz cement volumes are based on stylolite insoluble residue thickness and weight measurements of pyrobitumen within and nearby the insoluble residue seams. Stylolitization of K-feldspar and precipitation of muscovite can release additional silica which may have precipitated as quartz cement.

The nomenclature of phyllosilicates is discussed in relation to structural variations of layers and interlayers. Some discrepancies in the nomenclature which arose due to historical reasons and different viewpoints may be reconciled if the choice of the construction units (layers or their parts) is related to definite sets of structures for which these units are common. Features of idealized models approximating real structures should be considered for classification and derivation of nomenclature sets, whereas priority is given to structural variations before lattice and symmetry characteristics. Layer polymorphs, pseudo-polytypes, polytypes (both simple and complex), and OD structures are distinguished. Particular results obtained for micas as a model example of phyllosilicates in relation to modular structures in general are considered in an Appendix.

Inverse gas chromatography at infinite dilution, employing alkanes and alkenes as probes, has been used to characterize the surface properties of a series of smectites of varying chemical composition. The results of this study show that the acidic centers and the interlayer distances have a great influence on the specific interaction of the smectite surface with π-bonds of alkenes. High values of the specific interaction parameter, ɛπ, are caused by the existence of strong acidic centers that are connected with interlayer cations as well as with the chemical structure of the mineral sheets. On the other hand, alkanes, whose interaction with the smectites is predominantly dispersive, are unaffected by changes in the clays’ composition and/or structure.

A procedure for structural investigations by X-ray diffraction of mixed-layer structures incorporating swelling layers has been developed. For each sample, specimens saturated with different cations (Na, Mg, and Ca), are analyzed both as air-dried and as glycolated. One structural model fitting all the observed patterns then provides the structure of the sample. Samples tested include: Mite-smectite (I-S) minerals from Kazachstan (a rectorite), Dolna Ves in Slovakia, Kinnekulle in Sweden, the North Sea, and Scania in Sweden. The fitting of the patterns of the Kazachstan rectorite demonstrated that the instrumental parameters applied in the modeling were correct. For the I-S minerals from Slovakia and Kinnekulle the observed patterns were fitted with one two-component I-S model. However, the Ca-saturated and air-dried specimen of the Kinnekulle bentonites had two types of swelling interlayers. For the Slovakian I-S with Reichweite = 2, an alternative two-phase I-S plus I–V (V = vermiculite) model fitted the experimental X-ray diffraction patterns equally well. The I-S mineral from Scania is in fact a three-component I-T-S (T = tobelite) and the North Sea sample is a four-component I-S-V-V, one type of the swelling layers having swelling characteristics intermediately between smectite and vermiculite. In addition to layer types and distribution, interlayer compositions, such as the amount of interlayer glycol and water and of fixed and exchangeable cations, were determined.

The full structure of dickite from St. Claire, Pennsylvania, including hydrogen atoms, was refined in space group Cc using time-of-flight neutron powder diffraction data obtained at 12 K and Rietveld refinement/difference-Fourier methods (Rwp = 2.62%, reduced χ2 = 1.915, 113 variables, a = 5.1474(6)Å, b = 8.9386(10)Å, c = 14.390(2)Å, and ß = 96.483(1)°). The non-hydrogen structure is essentially identical to published structures for dickite, but the hydrogen positions are distinct. The inner hydroxyl group is approximately parallel to the (001) plane, inclined by 1.3° towards the tetrahedral sheet. Contrary to published low-temperature infrared (IR) spectra, there is no evidence that dickite possess lower symmetry at low temperatures although there is tentative evidence for statistical occupancy of H3 on more than one site. Low-temperature IR spectra of St. Claire and Wisconsin dickites do not show evidence for more than four hydroxyl groups and are consistent with the reported structure. Upon cooling from 300 to 15 K, the position of the OH3 stretching band increased from 3710 to 3731 cm−1. This large, positive shift in frequency was attributed to the increase in the internuclear O-H3 ⋯ O distance upon cooling. The frequency of the 3655 cm−1 band initially decreased by 2 cm−1 to 3653 cm−1 upon cooling from 300–125 K; however, the band increased in frequency by 1 cm−1 upon further cooling to 15 K. This unusual change in frequency upon cooling is consistent with the assignment of this band to OH2 and OH4. The position of the OH1 stretching band decreased from 3622 to 3620 cm−1 upon cooling, which was attributed, in part, to the observed increase in the Al-O(H1)-Al angle at low temperature.

The effect of anions on clay dispersion and the hydraulic conductivity (HC) of clay-sand mixtures has received little attention. This study investigates the effect that adding small amounts of anions has on the dispersivity and HC of reference clays. Mixtures of 3 and 6 g 100 g−1 kaolinite, smectite, and illite with quartz sand were packed in columns. The columns were saturated with Ca and then leached with 1 molc m−3 of one of the following organic and inorganic Na salts: chloride, hydroxide, EDTA, silicate, citrate, formate, oxalate, hexametaphosphate, orthophosphate, tartrate, or humate. Changes in HC and clay concentration in the effluent were measured and clay dispersion was evaluated as a function of the various anions added. In the kaolinite clay-sand mixtures, a significant amount of clay was observed in the effluent for all anions tested, and the HC increased above its original value. The HC of smectite clay-sand mixtures decreased following the addition of the various anions. Dispersed clay appeared in the effluent only upon addition of citrate or hexametaphosphate. In the latter two cases, the HC started to increase once maximum clay concentration appeared in the effluent. Clay concentration in the effluent of smectite was one order of magnitude lower than that of kaolinite. Illite clay-sand mixtures showed dispersion behavior intermediate between smectite and kaolinite but behaved in the same way as kaolinite with respect to HC changes.

Historically, the decarbonation of Mg-Al-CO3 hydrotalcite-like compounds (HTlc) has been thought to occur between 400° and 500°C. The present work demonstrates that when HTlcs having the maximum Al content, Al/(Al + Mg) = 0.33, are heated to 500°C, 20–30% of the carbonates remain. The evolution of the remaining carbonates was observed as two maxima, at 600 and 900°C At these temperatures, Al ions go into MgO, and spinel (MgAl2O4) forms. Therefore, the carbonates are released as the Al ions migrate.

At a lower Al content, Al/(Al + Mg) = 0.25, CO2 evolution is almost complete at 500°C. This HTlc has no maximum of CO2 evolution above 500°C. Lower charge densities, due to lower Al contents, lead to lower amounts of remaining carbonate anions.

Fine clays (<0.1 μm) extracted from an acid soil developed in a granite saprolite from the Massif Central, France, were characterized by X-ray diffraction (XRD) using a curve decomposition program, and high-resolution transmission electron microscopy (HRTEM) associated with a method of impregnation of moist samples. Direct measurement of d-spacings were performed on HRTEM photographs. Decomposition of XRD patterns indicated 5 to 6 different clay phases including chlorite (and/or hydroxy-interlayered vermiculite), vermiculite/smectite, illite/vermiculite and illite/smectite mixed layers. Expandable phases with decreasing layer charge (vermiculite, high- and low-charge smectite) were shown in the clay assemblage. When performed on K-saturated samples subjected to wetting and drying cycles, HRTEM observations were consistent with the XRD results. The major clay mineral phases identified by the decomposition of XRD patterns were also found by direct measurement of d-spacings on HRTEM images. Vermiculite and high-charge smectite appeared to be impregnated with preservation of their initial hydration state, whereas low-charge smectite interlayers were penetrated by the resin molecules during the impregnation procedure. It was concluded that the decomposition of XRD patterns gave a realistic analysis of the clay phases present in a complex soil clay sample, as well as the direct measurement of a limited number (50) of clay crystals on HRTEM images.

The adsorption of the herbicide dimepiperate S-(α;α-dimethylbenzyl)-1-piperidinecarbothioate on homoionic Fe3+-, Al3+-, Ca2+-, and Na+-montmorillonite was studied in aqueous medium. The adsorption is described well by the Freundlich equation. The adsorption capacity decreases in the order Fe3+ > Al3+ > Ca2+ > Na+ clay. The dimepiperate adsorption from chloroform solution was also investigated by analytical, spectroscopic, and X-ray powder diffraction techniques. IR results suggest that the adsorption involves the interaction of the thioester carbonyl group of dimepiperate possibly with the surrounding water of metal ions. On Al3+ and Fe3+ clays, this interaction leads to hydrolysis of the thioester bond and formation of the thiol and carbamic acid derivatives that yield α-methylstyrene and piperidine, respectively.

Boron sorption by hydrous Al-oxide was studied as a function of concentration, pH, temperature and in the presence of oxalate and phosphate. For comparison sorption of B was also measured with charcoal as adsorbent.

At constant pH a Langmuir type equation was found to fit the results well at pH values below 7.2 where only boric acid molecules are present in solution. B sorption was dependent on pH with maximum sorption at pH 8.5. Oxalate and phosphate ligands form strong bonds to AI and were found to reduce B sorption. Sorption of boric acid molecules decreased with increasing temperature and the isosteric heat of reaction was 13.8 kJ mol−1. These results indicate that there are two mechanisms of sorption on hydrous Al-oxide, physical sorption of boric acid molecules and ligand exchange (chemisorption) of borate, and both mechanisms are favored onto the oxide.

X-ray photoelectron spectroscopy (XPS) has been used to characterize the bonding state of Cu2+, Si4+, Al3+, and O2− ions in structural (octahedral and interlamellar) or adsorbed position in phyllosilicates. Five smectites, 5 kaolinites, and 1 chrysocolla with Cu(II) in known positions (octahedral, interlamellar, or surface adsorbed) have been investigated. Their spectra were compared with those of pure Cu metal and of pure Cu(I) and Cu(II) oxides.

The line for Cu 2p3/2 (binding energy of 935.4 eV) and well-defined shake-up lines (binding energy of about 943 eV) observed after 1 hr of X-ray irradiation are characteristic of Cu(II) in phyllosilicate octahedral sites. But due to the photoreduction effect, they show Cu(I) oxidation states (Cu 2p3/2, binding energy of 933.2 eV and near absence of shake-up lines) for the phyllosilicates with adsorbed Cu or in interlamellar positions. The kinetics of photoreduction distinguishes octahedral from interlamellar positions, and the latter from a surface adsorbed position. The enlargement of the FWHM (full width at half maximum) of XPS lines has been used to describe crystallochemical parameters linked to local ordering around the probe cations. Crystallization produces decreasing O 1 s and Cu 2p (octahedral cation) line widths but has no effect on the Si 2p (tetrahedral cation) line width. The enlargement of FWHM for all ion lines of the lattice is linked to the nature (Cu > Mg > Al) and the number and amount of structural cations in the phyllosilicates.

The crystallization kinetics of goethite were studied colorimetrically under highly alkaline conditions (pH 10.1–12.2) at temperatures from 40° to 85°C. Color changes during crystallization from fresh precipitates, plotted on a*-b* colorimetric diagrams, were used to discriminate between pure goethite and mixtures of goethite and hematite. Only the b* value increased as goethite crystallization proceeded, and even a minor increase in the a* value revealed the existence of hematite. The rate of goethite crystallization, estimated from the b* value, could be modeled by a pseudo-first-order rate law. This rate depended both on pH and on temperature. Apparent activation energies for the reactions of 56.1 kJ/mol at pH 11.7 and 48.2 kJ/mol at pH 12.2 were estimated from Arrhenius plots.

Ludox HS SiO2 sols at high concentrations show a peak in small angle x-ray scattering (SAXS) reminiscent to a “structure.” The appearance of such a peak was found to depend crucially on the thickness of the sample cell used for SAXS measurements. The thinner the cell used, the more prominent the peak. When the thickness was larger than 2 mm, it was no longer observable. When sols were treated with activated charcoal powders (in order to remove a surfactant) the peak became less prominent.

For the cases where clear features for structure were absent (thick sample regime), the Smoluchowski scheme was utilized to study the nature of sols. Namely, the distribution of the Smoluchowski species were estimated by numerically calculating the size distribution of particles directly from SAXS data. The distribution was found basically bimodal, and the main distribution peak, particularly for dilute sols (less than 5 wt%), was consistent with primary particles of SiO2. The second distribution peak was strongly dependent on the concentration of SiO2 particles. The observed trend was that the higher the concentration of SiO2 particles, the more prominent the second distribution peak and the locus of the maximum tended to move toward a smaller value in diameter. This behavior of the second distribution peak of the Smoluchowski species is no doubt a manifestation of the interparticle correlation. The observation of such behavior may provide a convenient means to characterize sols with interparticle correlation. This method was also applied for characterizing gels formed when the pH values were altered.

The Madayi clay deposit consists of a thick sequence of residual white kaolinitic clay underlying the sedimentary Warkallai Formation, which includes gray carbonaceous kaolinitic clays, lignite, ferruginous kaolinitic clays, laterite and bauxite with ferricretes. The conditions of clay genesis and the economic significance of the major residual kaolin seam have been investigated. The raw clay and <2 μm fractions were subjected to X-ray diffraction (XRD), chemical analysis, differential thermal analysis (DTA), Fourier transform infrared (FTIR) spectroscopic and scanning electron microscopic (SEM) studies. The firing behavior of the <45 μm fraction of the major residual clay sequence (L), was investigated systematically to determine the potential industrial use of this kaolin.

Geochemical and morphological studies of different strata indicate the following conditions for clay formation. (1) intense lateritized weathering conditions for kaolinization of the residual white clay from parent quartzo-felspathic mica-gneiss. (2) reducing environment for the gray carbonaceous layers; an. (3) oxidizing environment for the uppermost hematite-rich ferruginous clay. Pyrite/marcasite enriched detrital gray carbonaceous clay shows two distinct environments for in situ kaolinite crystallization. (1) within plant fossils influenced by the high organic content and FeS2 leaching; and (2) precipitation from solution.

Incomplete kaolinization of white residual clay is evident from the presence of pyrophyllite, muscovite with lenticular cleavage void and a lower percentage of fines (<2 μm). The plant fossils from the uppermost portion of residual clay show pyrite mineralization. The Hinckley Index, FTIR and rare earth analysis point towards diverse geochemical environments of deposition and technological evaluation indicates its suitability for application in the ceramics industry.

In the copper deposit of Salobo 3A (Brazil), nontronite-like clay samples were found at the bottom of the weathering blanket. Samples were fractionated first by sedimentation and then by a HGMS method. From XRD data, it was found that the samples are essentially smectite with kaolinite in very small quantities. The average structural formula of the smectite, presented in the traditional manner, is:

Chemical analyses show that the smectite samples contain a population of clay particles whose chemistry ranges between a nontronite end-member and an Al-Mg beidellite end-member.

Spectroscopic studies by FTIR, Mössbauer, and ESR show that the three major octahedral cations (Al, Fe, Mg) are present in each octahedral sheet of the smectite, forming a solid solution, and that the chemical trends of the smectite clay detected at a “macroscopic” scale (associated clay particles) can also be observed at the unit cell scale.