Long-range ordering of tetrahedral cations in micas is favored by phengitic compositions, by the 3T stacking sequence of layers, and by tetrahedral Si:Al ratios near 1:1. Phengites of the 1M, 2M1, and 2M2 polytypes are said to show partial ordering of tetrahedral cations, although the amounts of tetrahedral substitutions are small and the accuracies of determination are not as large as desired. The 3T structures of muscovite, paragonite, lepidolite, and protolithionite show tetrahedral ordering, as do the 2M1 brittle micas margarite and an intermediate between margarite and bityite. Muscovite-3T and margarite-2M1 are also slightly phengitic relative to their ideal compositions. Examples of octahedral cation ordering in micas are more abundant and are to be expected when cations of different size and charge are present. Octahedron M(1) with its OH,F groups in the trans orientation tends to be larger than the mean of the two cis octahedra as a result of the ordering of cations and vacancies. In some samples ordering has reduced the true symmetry to a subgroup of that of the ideal space group. If ordering in subgroup symmetry results in ordered patterns of different geometries but similar energies in very small domains, the average over all unit cells may simulate long-range disorder.

The reactions of the tris(acetylacetonato)silicone(IV) cation (Si(acac)3+) with Na+-, Mg2+-, and Co2+-exchange forms of hectorite and montmorillonite have been investigated to understand better the formation process of clays pillared by silicic acid. In acetone as the solvating medium, Si(acac)3+ binds to the Na+- and Mg2+-clays with the desorption of only a small fraction (~5%) of the initial exchange cation, suggesting that the complex binds as the ion pair [Si(acac)3+][Cl−]. With the Co2+-clays, however, the exchange cation is desorbed quantitatively, and Si(acac)3+ binding is accompanied by the formation of an acetone-solvated CoCl2 solution complex which helps to drive the ion-exchange reaction. Thus, Co2+-smectites react with Si(acac)3+ in acetone to produce homoionic Si(acac)3+ intercalates, whereas Na+-and Mg2+-smectites produce mixed-ion intercalates. The interlayer hydrolysis of Si(acac)3+ to silicic acid in the homoionic Si(acac)3+- and mixed-ion Na+/Si(acac)3+- and Mg2+/Si(acac)3+-exchange forms of montmorillonite films is diffusion controlled. In water as the solvating medium, the reaction of Si(acac)3+ with Mg2+- or Co2+-montmorillonite results in the desorption of the exchange cations on a time scale which is comparable to that observed for the solution hydrolysis of Si(acac)3+. Thus, the precipitation of silicic acid from aqueous solution competes strongly with the formation of interlayer silicic acid. With aqueous Na+-montmorillonite dispersions, however, a significant fraction of the exchange cations desorbed rapidly upon Si(acac)3+ binding, and the formation of interlayer silicic acid is favored over the precipitation of Si(OH)4.

Interaction of La3+- and Ce3+-exchanged hectorites with oligomeric hydroxy-Al cations results in the formation of cross-linked hectorites possessing moderately high surface areas (~ 220–280 m2/g) and high thermal stability. The basal spacings of these products were generally in the range 17.0–18.0 A, the exact d(001) value depending on the age of the hydroxy-Al oligomeric solution and on the pH of the starting hectorite dispersion. Interaction of Li- or Ce-fluorhectorite with hydroxy-Al oligocations produced the corresponding cross-linked fluorhectorites, which showed markedly higher basal spacings (18.2–20.0 Å for air-dried samples), surface areas (~300–380 m2/g), and thermal stability, as compared with those of the cross-linked hectorites. The cross-linking agent applied in the synthesis of the hydroxy-Al hectorite and fluorhectorite products consisted of a solution of hydroxy-Al oligomers aged for periods of 7 to 27 days. A constant ratio of 2.0 mmole Al/g of smectite was used in all preparations. The high basal spacings and porosity of the newly synthesized products are consistent with a structure similar to that previously proposed for cross-linked hydroxy-Al montmorillonite.

Air-dried samples of homoionic Na-, Ca-, Al-, and Fe-smectite were equilibrated with 2,6-dimethylphenol vapor for 24 hr. Infrared spectra of the complexes formed indicated that a portion of the sorbed phenol was transformed into quinone-type compounds. Both sorption and transformation were greatly influenced by the nature of the exchangeable cation and followed the order Fe ≫ Al > Ca > Na. Changes in the electron spin resonance spectra of the clays following interaction with the phenol followed the same order, indicating that these reactions are enhanced by a transition metal cation, such as Fe3+, on the exchange complex. The reaction products from the clay complexes were extracted with methanol and identified using ultraviolet/visible spectrophotometry, high-pressure liquid chromatography (HPLC), and mass spectrometry. The extracts contained mixtures of products including the parent phenol, di-, tri-, and tetramers of the phenol, as well as quinone and quinone dimers. The identities of these compounds were further confirmed by the coincidence of the retention times of HPLC peaks obtained from extracts of the clays with those from compounds produced by oxidation of 2,6-dimethylphenol with Ag2O.

Goose Lake, Beavers Bend, and Fithian illites were equilibrated in the presence of goethite (or hematite) at room temperature for as long as 2.6 yr. Kaolinite of known stability was added to some samples. Samples of solution were obtained after centrifuging with, or without, immiscible displacement or column leaching. Equilibrium was indicated by constant values over a long period of time, with kaolinite solubility as an internal indicator, and most importantly, by the approach to equilibrium from both undersaturation and supersaturation. Data plots indicate that the illites contain two or more phases or components in equilibrium with each other. Statistical and graphical techniques were used to analyze hundreds of equilibrations. The constancy of pK values for various expressions indicates that bulk illite composition and pyrophyllite are likely solution-controlling phases or components, but that muscovite, leucophyllite, phlogopite, and talc are not. A muscovite-like phase, of lower K content than muscovite, fit one pK expression well, but failed on two others.

The coarse (2-0.2 μm) and fine (<0.2 μm) size fractions of several soil and reference kaolinite samples were completely intercalated and expanded to 11.2 Å using a simplified CsCl-hydrazine-di-methylsulfoxide (DMSO) treatment. Rapid equilibration of the clay in hot (80°C) hydrazine monohydrate and hot (100°C) DMSO, and the use of ceramic tile mounts, limited the sample pretreatment time to only 15 min. The fine size fraction of kaolinite may be X-rayed immediately after pretreatment, though analysis of the sample 2 or 12 hr after pretreatment produced more intense, sharp basal reflections. This difference may be due to a better ordering of the DMSO-kaolinite complex with time and to a drying of the excess DMSO. The coarse size fraction of kaolinite did not entirely expand to 11.2 Å when analyzed immediately after pretreatment. A 9.6-Å peak was also present and possibly represents a mixed layering of expanded and nonexpanded kaolinite layers. The larger crystals seem to require additional time for the reaction to become complete as evidenced by the presence of an intense, sharp 11.2-Å peak and absence of the 9.6-Å peak when the coarse clay was analyzed 2 or 12 hr after sample pretreatment. Kaolinite particles <50 μm did not react completely even when they were analyzed 24 hr after pretreatment. Therefore, this technique should be limited to <2-μm particles.

Simple equations are presented which allow double-layer potentials of clays to be derived from co-ion exclusion measurements in monovalent and divalent electrolyte solutions. These equations have been used to re-interpret earlier results for illite and montmorillonite. The potentials derived follow the lyotropic series for the various homoionic modification of each clay. We have demonstrated that the Schofield equation, which assumes high double-layer potentials, cannot be applied to co-ion exclusion in clay systems. Re-analysis of earlier measurements has shown that for a given homoionic clay the potentials are almost independent of concentration over the range 0.3 to 0.003 molar. Thus, clay surfaces appear to behave more like constant-potential than constant-charge surfaces.

Resilication of bauxite produced kaolin at and beneath an old erosion surface on bauxite at the Alabama Street Mine of ALCOA in Saline County, Arkansas. The transitional alteration can be traced in morphology by scanning electron microscopy, (SEM) and in Al:Si ratio by energy dispersive analysis. In one illustrated example, the sequence of resilication took place within 1 mm thickness; in another, across 80 mm. The first morphologic alteration of gibbsite (bauxite) appears to be to allophane that occurs in micrometer-size plates which show elongate cracking and/or straight to highly curved elongate edges. The next phase is kaolinite, first in micrometer-size flakes followed by coarser flakes that grade into a zone of typical stacked kaolinite, likewise identified by X-ray powder diffraction. Notably large stacks and small flakes of kaolinite are intimately mixed in the SEMs, thus suggesting that unequal sizes of kaolinite crystals can grow during one episode of an in-situ genesis.

White saponite occurs in joints and open fracture zones in metamorphosed dolomitic limestone near Ballarat, California. The saponite appears to have formed by hydrothermal alteration, possibly during Pliocene times. The material shows a 06l X-ray powder diffraction peak at 1.529 Å, A12O3 and MgO contents of about 4.4 and 23.5%, respectively, and a half-cell octahedral atoms summation value of about 2.82. The saponite appears to consist of a single, uniform clay species; the main impurities are fine shards of diopside and tremolite. The infrared and thermal properties of the Ballarat saponite are similar to those of the Allt Ribhein saponite. It has a lower water-holding capacity than montmorillonite and is characterized by lower Atterberg limits and expansion pressures and higher compaction densities. The apparent density of the saponite, 2.865 g/cm3, is greater than that of montmorillonite. This saponite is available from the Source Clays Repository of The Clay Minerals Society.