Chemical activity diagrarns, prepared to illustrate the properties expected if mixed-layer mont-morillonite/illite is regarded as a solid solution, are compared to those derived from a treatment of these materials as a mixture of two phases. If the system is a solid solution, the coexisting aqueous solution should range from higher dissolved silica contents in the presence of kaolinite and a montmorillonite end member to lower dissolved silica in the presence of kaolinite and an illitic end member. Silica concentration in the aqueous solution might vary by a factor of as much as six. If the system is two phase, the silica content of a solution in equilibrium with kaolinite and both phases would be fixed at a given T and P, as would a solution equilibrated with both phases and K-feldspar. In the absence of a third phase, silica in equilibrium with both phases should be nearly constant, but increase with increasing ratio of K+/H+ in solution. Available data on coexisting aqueous solutions apparently are more nearly consistent with two phases than with a solid solution.

The formation of fine-grained magnetite (~0.1 μm) at pH 7 and 25°C from aeration of Fe(II) chloride solutions is presented. The magnetite converted at 105°C to maghemite with poorly developed superstructure lines. Under the experimental conditions employed, as the initial [Cl]/[Fe] ratio was increased from the stoichiometric value of 2, the final product contained increasing amounts of lepidocrocite. The degree of crystallinity of this phase, as measured by the width at half height of the 020 X-ray diffraction peak, also increased with this ratio. The hydrolysis rate (base consumption to maintain pH) showed a plateau whose position and extent changed with the initial [Cl]/[Fe] ratio. Through this plateau region the Eh decreased to a minimum value the position of which was directly related to the [Cl]/[Fe] value. The formation of lepidocrocite rather than magnetite is likely due to the high [Cl] where there would be increased difficulty for neighboring OH to condense and eliminate H2O. The formation of Fe-O-Fe bonds in this condensation would be impeded by Cl substitution for OH either in the first formed green rust stage or during its oxidation.

Diffractograms of lepidocrocites formed from the oxidation of Fe(II) chloride solutions at pH 7 and 25°C showed differential line broadening with (0k0) reflections being much sharper than (hk0) or (hkl). As the initial [Cl]/[Fe] ratio was increased from 2, crystallinity increased in all axial directions, as defined by the width at half height of diffraction peaks. At [Cl]/[Fe] ratios greater than ~8, the crystallinity did not increase further, and for reflections involving the a-axis direction, it appeared to decrease. Increased [Cl]/[Fe] ratios changed the rate of the oxidation/hydrolysis reactions. These variations reflect changes in the stability and/or composition of the intermediate green rust phase, (Fe(II)Fe(III) hydroxychloride) in the high [Cl] environment. The influence of the [Cl]/[Fe] ratio was related to the experimental conditions employed, especially where they influenced the rate of oxidation.

Well-crystallized ferrihydrite as indicated by its X-ray powder diffraction pattern and low solubility in acidified oxalate (Feo/Fet = 0.27) was formed by the oxidation of FeCl2 solution containing Si/Fe = 18 × 10−3. The crystallinity of ferrihydrites formed from the solutions containing Si/Fe > 18 × 10−3 was lowered as indicated by weaker and broader XRD lines and increased oxalate solubility. Ferrihydrites formed in the presence of silica did not give the differential thermal analysis exothermic peak between 350° and 450°C that is found for ferrihydrites prepared from the hydrolysis of Fe(III) salts. The transformation of ferrihydrite (formed at Si/Fe = 18 × 10−3) to hematite was inhibited by the presence of 1.48% SiO2 in the oxidation products.

The exchange of Rh(NBD)(Pϕ3)2+, Rh(NBD)(PMe2ϕ)3+, Rh(COD)(Pϕ3)2+, and Rh(PMe2ϕ)4+ on hectorite was studied in methanol/dichloromethane, acetone, dimethylformamide, and acetonitrile. At low initial Rh+ concentration and short contact times, ion exchange was the predominant process, and its selectivity and maximum capacity were solvent-dependent. High initial Rh+ concentrations, long contact times, and the most polar solvents favored intersalation and salt precipitation. In all experiments monolayers of complex formed in the interlamellar space and were very tightly held. The complexes retained their integrity on the surface even after removal of all solvent molecules.

Using Garfield, Washington, nontronite as the model mineral system, methods and apparatus were developed to prepare reduced suspensions in citrate-bicarbonate-dithionite (CBD) solution. These techniques were effective in removing excess, undesired solutes from reduced suspensions while maintaining a high Fe2+ content. They also enabled the preparation of dried, reduced films preferentially oriented with respect to the crystallographic c-axis. Supernatant solutions were collected and analyzed for Fe, Al, and Si, from which the extent of dissolution of the clay as a result of CBD treatment was assessed. Results indicated that very little Fe and Si were released to solution, but as much as about 8% of the total Al was solubilized. The highest levels of Al in solution were observed in CB treatments without dithionite.

A sample of ferripyrophyllite, a mineral with ideal composition Fe2SiO10(OH)2, was analyzed by Mössbauer spectroscopy, magnetization and magnetic susceptibility measurements. The iron is entirely ferric, and the main feature of the Mössbauer spectrum at room temperature is a single absorption line with isomer shift δ = 0.36(1) mm/sec due to iron in M2 sites. The line is broadened by a slight quadrupole splitting Δ = 0.18(1) mm/sec, the smallest yet reported for a sheet silicate. Weaker features corresponding to quadrupole doublets with relative intensities of 7% and 8% having δ = 0.43(1) mm/sec; Δ = 1.22(2) mm/sec and δ = 0.14(1) mm/sec; Δ = 0.59(2) mm/sec are assigned to ferric iron in nonequivalent octahedral and tetrahedral sites, respectively, giving the following formula, based on published chemical analysis: Ca0.05(Fe3+1.87Mg0.11Al0.09)VI(Si3.80Fe3+0.16Al0.04)IVO10(OH)2, where Ca is in interlayer sites. Ferripyrophyllite orders antiferromagnetically at 18(2)°K. The Mössbauer spectrum at 4.2°K consists of a single, resolved magnetic pattern with hyperfine field Bhf = 51.8 T. The relatively high Néel temperature compared with other dioctahedral ferric phyllosilicates provides further evidence that Fe3+ cations tend to be ordered on M2 sites within the octahedral sheet.

Activity expressions are presented for a six end-member, regular solution, site-mixing model for chlorites. The end members are ideal 14-Å chlorites for which experimental stability data are lacking. Estimates were made of the standard state 25°C and 1 bar molar 3rd law entropies, volumes, and the Maier-Kelley heat capacity coefficients. Experimental stability data from the literature for 14-Å chlorites were used with different sets of exchange energies, for cations on adjacent sites, to compute estimates of the standard state chemical potentials of the end members at 25°C and 1 bar. More experimental data are needed for an adequate definition of the exchange energies and the standard state chemical potentials. The model was applied to diagenesis in clastic reservoirs. Aqueous activity ratios of Mg2+:Fe2+ were computed as an equilibrium function of the corresponding molar ratios in authigenic chlorites. The aqueous activity ratio was independent of the chlorite Al content at a constant molar ratio of Mg2+:Fe2+ in the chlorite. The model predicts a wide range of molar Mg2+:Fe2+ ratios in authigenic chlorites in equilibrium with reservoir fluids. Trends in these molar ratios should be independent of the Al content in the chlorites. The model can be applied directly to 7-Å chlorites when experimental data become available to estimate the various thermodynamic parameters of the 7-Å end members.

Ferrous or ferric Perchlorate, 0.01 M, was reacted with calcite in stirred aqueous suspensions which were bubbled vigorously with an oxidizing purge gas. Two and three equivalents of CaCO3 were dissolved per mole of Fe2+ and Fe3+ neutralized, respectively. With Fe(ClO4)2, the crystalline Fe oxide products partially coated the calcite surface. The dominant products were lepidocrocite and goethite when the purge gas was air or 20% CO2 (balance air), respectively. After reaction with Fe2+ the edges and corners of the calcite crystals were generally rounded and the faces were non-uniformly pitted; however, after reaction with Fe3+, a mosaic pattern with distinct ridges and channels was evident on the calcite. These ridges were somewhat pitted, but distinct stepped dislocations were present leading to a featureless and generally flat channel floor. When the calcite was separated from the Fe solution by a semi-permeable membrane, precipitation occurred predominantly on the calcite side and on the Fe side of the membrane in the Fe2+ and Fe3+ systems, respectively.

Fe oxyhydroxides precipitated from the Fe(ClO4)3 and Fe(ClO4)2 solutions by different mechanisms. In the Fe(ClO4)3 system, although the initial reaction may have been at the calcite surface, the bulk of the poorly crystalline ferrihydrite was formed by hydrolysis of Fe polymers in suspension. Neutralization occurred by the reaction with basic products of a surface-controlled dissolution of calcite, rather than by a direct reaction of acidic polymers with the calcite surface. In the Fe(ClO4)2 system, lepidocrocite or goethite formed by the partial hydrolysis of Fe2+ or Fe3+ by reaction with calcite or the basic products of calcite dissolution and subsequent precipitation of simple Fe species on existing FeOOH nuclei.