The i.r. spectra of mixtures of different Na-montmorillonites were determined at several water contents between 2 and 22 g of water/g of montmorillonite. It was found that Si—O absorption is represented by four closely-spaced bands, one of which is pleochroic. The pleochroic band appeared only at higher water contents. All of these bands, excepting that with the highest wave number, shifted in frequency with increasing isomorphous substitution. None of them shifted in frequency with increasing water content.

The absorption coefficient for the principal Si—O absorption decreased with increasing isomorphous substitution but increased with increasing water content. Niether isomorphous substitution nor water content appeared to have any significant effect on absorption due to O—H stretching or H—O—H bending in the interlayer water.

At a critical water content for each montmorillonite, an abrupt change occurred in the absorption coefficient for the principal Si—O absorption. This change was ascribed to a sudden rearrangement of the particles.

The nature of the parent material from which flint clay or flint-like clay is derived may modify the texture of the clay as observed by SEM. Flint clays occurring in Pennsylvanian-age swamp basins into which were transported residues weathered from sedimentary country rock exhibit a texture of interlocked kaolin pockets and sheaves. On the other hand, flint clay or flint-like clay derived by weathering of volcanic ash exhibits a texture resembling, on a micro-scale, the scalloped, “oak-leaf” pattern of montmorillonite. The interpretation is that an expanding clay having a transitional role between the ash and the kaolinite is the donor source of the micro-scalloped pattern inherited by kaolinite. X-ray powder diffractograms of the clays support the interpretation.

A steady state reaction of apparent equilibrium of K mica + Ca2+ ⇄ Ca vermiculite + K+ was indicated by prolonged dissolution extractions from Blount soil clay (from northern Indiana) abundant in dioctahedral mica and vermiculite, with log Keq = 2.92 for the reaction when extrapolated to infinite time. From this and published free energies of formation of mica and kaolinite, a mineral phase stability diagram depicting the phase joins of Ca vermiculite, muscovite, and kaolinite was constructed with the solute activity functions pH-pK+, 2pH-pCa2+, and pSi(OH)4. These solute functions for 14-day reactions of calcareous (and dolomitic), poorly drained Harps soil (from central Iowa) fell near the calcite-dolomite-CO2-H2O phase join, suggesting equilibrium. These functions for Harps soil and the control minerals muscovite, biotite, and (or) vermiculite plus calcite were plotted on the mica-vermiculite stability diagram for various CO2 partial pressures. The points fell on the vermiculite-stable side of the mica-vermiculite plane at CO2 partial pressures of 0.15 and 0.20 atm (similar to soil air that would exist under frozen soil during winter and early spring; 2pH-pCa2+ ≃ 10.3). They fell on the muscovite-stable side of the muscovite-vermiculite plane at CO2 partial pressures of 0.0001 and 0.001 atm (similar to soil air under natural summer conditions; 2pH-pCa2+, 13.6 and 12.6, respectively) and therefore K+ (and 137Cs+ in rainfall) would be expected to be fixed.

The 2pH-pMg2+ values determined for Harps soil at the various CO2 partial pressures plotted either in the Mg montmorillonite stability field or on the Mg-montmorillonite-kaolinite phase join, in concordance with the abundance of montmorillonite and some kaolinite in the medium and fine clay fractions. The solute values for the nearby Clarion soil (upland, noncalcareous) plotted on the montmorillonite-kaolinite join, or with higher CO2 partial pressure, in the kaolinite stability area. The Gibbs free energy of formation (△Gf0) for a dioctahedral Ca vermiculite of −1303.7 kcal per 010 was determined from the Keq. The solute functions for the Blount soil showed kaolinite to be the thermodynamically stable phase with respect to dioctahedral mica and (or) vermiculite. The 14-day solute values for the Harps and upland Clarion soils were also on the kaolinite stability side of the kaolinite-vermiculite join. The kinetics of kaolinite formation in the upper midwestern U.S.A. are apparently slow on a scale of ~ 104 years.

The hydrothermal aging of pure silica—alumina gels in presence of 10 ml of 0.1 N sodium hydroxide solution at 175, 150 and 130°C for 8–30 days led to the synthesis of zeolites and the phyllosilicates, beidellite and kaolinite. The solution was neutralized by a partial hydrolysis of the gel which readily reorganized into a prezeolitic material. At pH values ⩾ 9, with 300 or 600 mg of gel, it evolved towards the crystalline zeolites P and S, with low surface area (7–100 m2/g) but high exchange capacity (300–475 m-equiv./100 g). With gel amounts of 600–2400 mg, and pH values of 8–5.5, the prezeolitic material provided rows of O—Si—O—Al—OH which recombined to form the phyllosilicate structures. Surface area increased (170–325 m2/g) but exchange capacity decreased (100–250m-equiv./100 g). The results obtained by various techniques (XRD, DTA, IR) indicated a moderate degree of crystallinity of these phyllosilicates; in addition, X-ray powder diffraction suggested that hk bands were the first to develop.

The positive results obtained with a 0.40 ratio Al2O3 gel compared with the negative results obtained with 0.30 or 0.50 Al2O3 gels indicate that the gel composition is very important for the formation of phyllosilicates under the experimental conditions.

The variation with time of exchangeable surface charge of amorphous ferric hydroxide in aqueous suspension was monitored by a titration technique. After 120 days, the surface charge of suspensions with initial pH from 8.5 to 10.5 was about one-fourth of the initial value, and goethite had formed from the ferric hydroxide. After the same time interval, the exchangeable surface charge of suspensions with initial pH from 5.5 to 8.0 was about two thirds the original value and the ferric hydroxide was still largely amorphous. The initial rate of crystallization and surface charge reduction increased with initial pH for suspensions with pH from 8.5 to 10.5, whereas the rate of surface charge reduction appeared to be independent of pH for suspensions with initial pH between 5.5 and 8.0. Based on these results it is suggested that at pH from 8.5 to 10.5 ferric hydroxide ages to goethite via a solution stage involving the Fe(OH)4- ion, whereas at pH values below 8.5 ferric hydroxide aging proceeds via mechanisms which do not involve the particle surface or bulk solution.

The structural formula for K and Mg saturated beidellite was calculated from the total elemental analysis of the < 0.2 μm clay fraction of the B2t horizon of a Mexico soil. The free energies of formation (ΔGfo) of K-beidellite and Mg-beidellite as determined from their apparent solubilities were -2491.3 and -2484.0 ± 3.2 kcal per mole, respectively. The free energies of formation correspond to a clay mineral structure calculated on the basis of a 24 oxygen cell.