The thickness of the two-layer ethylene glycol complex of dioctahedral smectites varies under room conditions between 17.3 and 16.5 Å because of such factors as layer charge density, type of interlayer cation, and relative humidity. Neglecting this variability can give up to 30% error in the X-ray powder diffraction estimation of the smectite:illite ratio of the mixed-layer structures. Three methods have been developed for the interpretation of X-ray powder diffraction patterns of glycolated mixed-layer illite/smectite which take layer-spacing variability into account. The methods include a technique for quantifying the degree of layer ordering. In addition, the proposed techniques minimize the error due to the influence of domain size on positions of reflections. The experimental error can be kept below 5% or below 1% smectite layers, depending on the method applied, provided that the peak positions are measured with the accuracy of ± 0.02°2θ.

A regularly interstratified chlorite/vermiculite occurs in red beds of the East Berlin Formation (Early Jurassic age) in the Connecticut Valley. The mineral is restricted to a 2.5-m wide zone of contact metamorphosed strata adjacent to and underlying the Hampden Basalt. Chemical and X-ray powder diffraction data indicate that the chlorite/vermiculite formed in response to lava-induced elevated temperatures and the availability of magnesium in the muds during and shortly after emplacement of the lava flow. Near the contact, hydrothermal fluids originating from the lava and from the synchronal weathering of basalt fragments by superheated pore waters provided a source of Mg. Further from the contact, magnesium was primarily derived from the thermal dissociation of dolomite. K2O concentrations and the distribution of clay minerals in the red mudstone suggest that the interstratified chlorite/vermiculite formed from preexisting illite or vermiculite as potassium was released and brucitic sheets were incorporated into interlayer positions.

The hydroxyl orientations in the 2H2 polytype of amesite, Mg2Al(SiAl)O5(OH)4, have been determined by minimizing the electrostatic potential energy as a function of OH orientation. The angles, ρ, between the hydroxyls and (001) vary between 81.5 and 88.8°. All surface hydroxyls form hydrogen bonds with oxygens of the adjacent layer. The OHs tend to tilt away from the higher charged A1VI ions, and the spread in ρ values is due to variations in the positions of the receptor oxygens. The inner hydroxyls noticeably weaken the interlayer bonding. The substitution of Al in both T and M sites creates a dipolar layer charge and the resulting attraction between layers forms an important part of the interlayer bonding. The 2H2 polytype of amesite has substantial interlayer bonding even with all surface hydroxyls replaced by fluorine. This is not true for a composition of Mg3Si2O5(OH)4 where a similar F for OH substitution destroys all interlayer bonding as in kaolinite.

Two variables must be considered when calculating exchange free energies (ΔG°ex) for 2:1 clays: (1) anionic field strength, as expressed by equivalent anionic radius (ra), and (2) interlayer water content, as expressed by interlayer molality. For smectites that are in a state of high hydration, interlayer molality is determined by the cations undergoing exchange. Thus ΔG°ex for an exchanging cation pair can be calculated solely from measurements of ra. ra is related to layer charge per half unit cell (C) and ab unit cell area (A) by: ra = (-A/8πC)1/2. The layer charge necessary for cation fixation can be predicted by calculating the ra at which cation exchange with an illite structure expresses a AG°ex equal to that of exchange with a smectite structure. The theory can also be applied qualitatively to understand the high selectivity of illite for Cs+, the fixation of K+ rather than Na+ in shales during diagenesis, the stability of illite over muscovite in the weathering environment, and cation segregation in smectite.

The Tulameen coal field is part of an Eocene nonmarine basin which received extensive volcaniclastic sediments due to its location within an active magmatic arc. Bentonite partings in the coal originally consisted of glassy rhyolitic tephra with phenocrysts of sanidine, biotite, and quartz. During the initial alteration, which took place within the swamp or shortly after burial, glass was transformed to either smectite-cristobalite-clinoptilolite or to smectite-kaolinite. The formation of kaolinite depended on the degree of leaching of silica and alkalies in the swamp environment. Some beds are nearly 100% kaolinite and can be designated as tonsteins. The smectite shows no evidence of interlayering; the kaolinite is well ordered. During alteration, sodium, originally a component of the glass, was lost from the system.

A later thermal event, which affected only the southern part of the basin, metamorphosed the smectite to a regularly interstratified illite/smectite with 55% illite layers and rectorite-type superlattice (IS-type). The source of potassium was dissolution of sanidine. Vitrinite reflectance measurements of the coal suggest that the smectite was stable to 145–160°C, at which temperature it transformed to K-rectorite.

The absence of randomly interstratified intermediates, even in beds rich in potassium, suggests that the transformation of smectite to K-rectorite was controlled by a steep thermal gradient possibly resulting from local magmatism or circulating geothermal fluids.

Zn- and Ca-adsorption equilibria of five Ca-saturated halloysite samples were measured at equilibrium Zn concentrations up to 10−2 M in 10−4 to 10−2 M CaCl2. The results were interpreted on KCaZn vs. [Zn]/CEC (%) plots, where KCaZn is the selectivity coefficient (= [Zn][Ca]/[Ca][Zn]), Zn and Ca represent the adsorbed species, and CEC is the cation-exchange capacity. All Zn adsorption occurred at cation-exchange sites, and 0.77 to 36.0 meq Zn/100 g clay, which constitutes 9 to 83% of the CEC, was adsorbed with “high selectivities” (KCaZn > 10). The higher values were found for two spherical and one “filmy” halloysites, whereas the lower values were found for two tubular halloysites. The magnitude of their 001 intensity, hydration in interlayer space, CEC, and “free” iron oxide content did not correlate with the selective Zn adsorption, but a good correlation was found between the proportion of “high selectivity” sites for Zn and proportion of “high affinity” sites for H+. The adsorption of Zn at the “high selectivity” sites was not completely reversible, and KCaZn values >1000 were recorded in 0.5 M CaCl2 for Zn which occupied 10–40% of the exchange sites. Selective Zn adsorption decreased with decreasing pH, and all adsorbed Zn was extracted with 0.1 M HCl.

Adenosine-5-phosphates (ATP, ADP, AMP) are adsorbed by clay minerals at very low concentrations (≤2 mg/liter). In contrast to quartz, the clay minerals exhibit a strong preference for ATP over AMP. The experimental data are expressed as recovery rates (adenosine-phosphate in solution to total nucleotide added). For example, the recovery rates of ATP, ADP, and AMP in the presence of sodium montmorillonite are 0,17, and 100%; in the presence of quartz 95, 100, and 99%. The recovery rate of AMP on clays is markedly decreased by the presence of ATP, that is, ATP increases the adsorption of AMP by cooperative interactions.

A part of ATP not recovered in the equilibrium solution is dephosphorylated to ADP. For example, 45% of ATP not recovered in equilibrium solution with calcium montmorillonite is recovered as ADP; with sodium montmorillonite only ADP can be recovered in solution.

Samples containing allophane with molar Al/Si ratios from 1.0 to 2.0 have been examined by infrared spectroscopy, X-ray fluorescence, and phosphate adsorption methods. The infrared spectra of allophane with Al/Si ratios close to 2.0 showed that the wall of the allophane spherules is made up of imogolite structural units similar to “proto-imogolite.” X-ray fluorescence gave no clear evidence of Al in tetrahedral sites (AlIV), while pyridine adsorption results suggested that a small number of Bronsted acid sites (AlIVOH) are present in silica-rich allophanes. Lewis acid sites (AlH2O) are present in both silica-rich and alumina-rich allophanes. The results suggest that the framework for the allophane structure is an Al octahedral sheet.

Allophanes with Al/Si ratios close to 1.0 contain condensed silicate units either on the outside surface of the Al octahedral sheet, giving rise to a halloysite-like structure, or bonded on the inside surface of an imogolite-like structure. Allophanes with Al/Si ratios between 1.0 and 2.0 appear to be mixtures of the “proto-imogolite” structure and the allophane (Al/Si = 1.0) structure.

High resolution imaging by transmission electron microscopy has revealed a mechanism for the weathering of intermediate microcline in a humid, temperate climate. Dissolution of the feldspar begins at the boundary of twinned and untwinned domains and produces circular holes which enlarge to form negative crystals. Amorphous, ring-shaped structures develop, about 25 Å in diameter, within the larger holes. These rings, in turn, crystallize to an arcuate phase having a 10-Å basal spacing and then to crinkled sheets of illite or dehydrated montmorillonite. The 10-Å layer silicate shows an irregular stacking sequence, including 10-,-20-, and 30-Å sequences. Included plagioclase crystals show a similar mechanism of weathering and, moreover, are more intensely weathered.

Model cation-exchange curves are presented for an idealized kaolinite surface where the charge on the surface (1) has its origin in cation substitution in the structure, and hence, is pH independent; and (2) is produced by protonation/deprotonation reactions of oxide-like sites, and hence, depends on the acid and base strengths of the surface sites, as well as the ionic strength. Two pH-independent situations are considered: one where the exchanging ions have no selectivity for the surface and are all in the diffuse layer; and one where selectivity exists for one ion and where that ion is partly in a Langmuir-Stern layer and partly in the diffuse layer. If one of the exchanging ions is a proton, the shape of the curves and their position on the pH scale depend on ionic strength and ionic selectivity.

The model curves are compared with data for actual kaolinites. Under most conditions exchangeable Al is released from the structure, and the shape of the charging curves becomes similar to that of an oxidelike surface. However, if titration is carried out rapidly, or account is taken of the presence of Al, the proton binding curves are similar in shape to those expected for sites resulting from cation substitution in the structure of kaolinite, either near the surface or at the edge of the crystal.

Ion-exchange experiments in expanding clay minerals conducted over a wide range of surface ionic compositions and ionic strength produce variable mass-action selectivity coefficients. When the exchanging ions are of unequal charge, tactoid structure appears to influence selectivity, although configurational entropy of adsorbed ions may also generate variable selectivity. The degree of deviation from ideal mass-action exchange is related to the dissimilarity of the ions undergoing exchange. Data involving trivalent ion adsorption on smectites suggest that mass-action is a poor approximation when the adsorbing and desorbing ions have different hydration energies and charge. No form of exchange equation is successful in describing ion exchange for a wide range of experimental conditions, although the fluctuation of the selectivity coefficient follows consistent trends with changing experimental conditions. The strong adsorption of high-charge ions on clays is not exothermic, but must be driven by the increasing disorder of ions and/or water.

Chloride-, sulfate-, and perchlorate-exchanged forms of hydrotalcite have been prepared and their layer spacings determined after equilibration in hydrous atmospheres and after heat-treatments up to the temperature of decomposition in the range 300–400°C. The initial carbonate form of hydrotalcite and also brucite, for purposes of comparison, have been similarly studied. Only chloride-hydrotalcite and brucite exhibit a single phase stable to the decomposition temperature. The other anionic forms exhibit various phases with different layer spacings which are interpreted in terms of the size, orientation, and stability of the anions and, in some cases, the presence of additional water. A regularly interstratified form of sulfate-hydrotalcite (layer spacing = 19.80 Å) is obtained at room temperature and relative humidity <50%; at higher humidities, a fully hydrated phase is obtained, and at 50°C a collapsed form is obtained. In the preparation of perchlorate-hydrotalcite, an interstratified phase (layer spacing = 17.0 Å) was recognized with alternating carbonate and Perchlorate layers, although the evidence is less certain.

Differences were found in the differential thermal analysis curves and in the temperatures of new-phase development between allophanes of high (1.91–1.99) and low (1.47–1.53) SiO2/Al2O3 ratios. The endothermic peak due to continuous dehydration and dehydroxylation was at higher temperatures (153°-185°C) for allophanes with high SiO2/Al2O3 ratios and at lower temperatures (148°–165°C) for those with low SiO2/Al2O3 ratios. The temperature of the exothermic peak was lower and the height affected more by the exchangeable cation content for allophanes with high ratios than for those with low ratios. New phases did not develop in allophanes having high Si02/Al2O3 ratios even after they were heated to 1000°C, above the temperature of the exothermic peak. In contrast, a symptomatic development of new phases was noted in allophanes with low SiO2/Al2O3 ratios at 900°C, below the temperature of the exothermic peak. The effect of SiO2/Al2O3 ratio in the thermal behavior of allophane strongly suggests that differences in the structure are closely associated with the chemical composition of this material.

The pH, Eh, electrical conductivity (EC), and the amounts and valency of replaceable iron were measured periodically on Fe2+- and Fe3+-saturated montmorillonite and cation-exchange resin at three temperatures. Differences in the pattern of change of pH, Eh, and EC with time appear to be related more to the histories and modes of preparation of the systems than to intrinsic differences in the hydrolysis of the iron in them. Electron transfer reactions involving crystal components of the clay can cause oxidation of adsorbed Fe2+ ions; the activation energy (Ea) for oxidation on the clay's surface was 6 kcal/mole, less than a third of the activation energy reported for Fe2+ oxidation in solution. In the Fe2+-resin, where Ea = 10.7 kcal/mole, perturbed surface-water molecules may act as electron acceptors enhancing Fe2+ oxidation.

Polymerization and precipitation of the adsorbed iron is affected by the necessity to maintain electroneutrality, the ability of the iron-hydroxy ions and small polymers to move about in the voids of the ion exchanger, and the steric hindrance posed by the matrix of the ion exchanger to the formation of large polymers. In resin, little or no iron precipitates, probably due both to steric hindrance and the inability of the resin to release ionic components to maintain electroneutrality. In clays, steric hindrance is small, and Al and Mg are released from the crystal to maintain electroneutrality, thus the precipitation of iron is abundant and is controlled by the rate of release of Al and Mg from the crystal.

In the absence of oxygen, Fe(II) chloride, sulfate, and carbonate solutions react at pH 6.5 to 7 with aluminum hydroxide suspensions to form new Fe(II)-Al(III) hydroxy anion compounds of the pyroaurite group. The Fe(II)-Al(III) hydroxy-chloride and -sulfate compounds are isostructural with Fe(II)- Fe(III) “green rust” compounds with A1 essentially substituting for Fe(III). Where CO32- is the only anion in the system, an Fe(II)-Al(III) compound isostructural with hydrotalcite is formed. Either in the dried or wet state, these compounds are unstable in air due to oxidation of Fe(II). Oxidation of the dried sample in air yields akaganeite or aluminous ferrihydrite, whereas, if the sample is maintained in a moist condition and oxidized by air under water, lepidocrocite or aluminous goethite is produced along with small amounts of ferrihydrite. On X-ray powder diffraction, the lepidocrocite so formed commonly shows no diagnostic (020) basal reflection, or one with a markedly reduced intensity. The products of oxidation, and the rapidity of their formation, appear to be dependent on the composition of the initial double hydroxy compound and the conditions under which the oxidation is carried out.

The green colored compounds commonly observed in gleyed soils also rapidly become yellow brown on exposure to air, and difficulty arises in the identification of the Fe oxide phases assumed to be present. Similar conditions and reactants to those involved in the formation of the compounds described above are expected in these soils, and it is suggested that Fe(II)-Al(III) members of the pyroaurite group may form in such an environment.

Neutron diffraction measurements for a preferentially oriented aggregate slab sample of deuterated Na-montmorillonite from Upton, Wyoming, are described for a series of clay-water contents ranging from 0 to 500 mg/g. A neutron wavelength of 2.39 Å was used with extended detectors to collect much of the “out of plane” component of the diffraction peak intensities.

The diffraction pattern intensities from the 00ℓ planes of the clay, corresponding to a reflection geometry, are a strong function of sample water content and show a variation in basal spacing from 9.8 to 19.0 Å. The hk reflections from transmission geometry measurements show, however, that the lattice a and b axes are constant within experimental uncertainty (0.02 Å) over the range in water content and their intensities vary only by a few percent. In this geometry, a broad, water-like diffraction pattern was noted as a background under the usual hk peak intensity series. This underlying water-like pattern varies in proportion to the sample water content.

Data reduction steps included consideration of background removal, multiple scattering, flux normalization, and attenuation of scattering due to sample thickness. Analysis of the reduced data revealed that the clay-water has a “liquid-like” ordering, with a density increase of approximately 5% over bulk water. An association between a few interlayer water molecules and the silicate superstructure is indicated by the slight change in the hk band intensities, but this change seems to be complete at water contents below 100 mg/g. Fourier analysis of the basal peak series from the dry clay shows that the hydrogens of the lattice hydroxyl groups lie in the same basal plane as their associated oxygen atoms.

Mixed-layer kaolinite/smectites containing 40–90% kaolinite layers have been synthesized from Wyoming smectite. Run times were 4 months at 156°C in solutions of A1C13∙6H2O and KCl or CaCl2. Similar KCl runs devoid of Al3+ yielded mixed-layer illite/smectites. The supply of Al3+, rather than pK or pH, seems to control the alteration of smectite toward kaolinite or illite.

A relation was derived which describes negative adsorption (salt exclusion) in systems in which double layer interaction takes place but where the surface potential remains finite, such as in clay pastes and sediments. Exclusion volumes calculated for montmorillonite pastes in equilibrium with 1:1 type electrolytes were found to compare favorably with data obtained by F. A. M. de Haan in an earlier study.

To explain the large values of the quadrupole splittings and line widths in the Mössbauer spectrum of oxybiotite, a formalized analysis of the distribution of effective charges in the anion network was conducted using an idealized model of the biotite octahedral layer. Based on this analysis, a qualitative physical model has been proposed, according to which the Mössbauer spectrum consists of a superposition of six quadrupole doublets. The proposed model explains the appearance of residual magnetization well below the biotite decomposition temperature. Annealing the biotite at 1070°K leads to the formation of nuclei of the magnetic phase in chains consisting of R3+ and vacancies. This phase is the decomposition product of biotite at 1370°K, i.e., a ferrispinel having Fe2−xMgAlxO4 (x = 0.5–0.6) composition.

Chelating organic acids hampered the hydrolytic reactions of Al and affected the nature of the crystalline aluminum hydroxides. Chemical composition, structure, size, nature of functional groups, and concentration of each organic anion, as well as the pH of the system, controlled the rate of Al(OH)3 crystallization. The order of effectiveness of the various acids was: glutaric < succinic = phthalic < glycine < malonic < glutamic < aspartic < oxalic < salicylic = malic < citric < tartaric. An increase in the stability of complexes formed between the organic ligands and Al decreased the rate of crystallization and changed the final aluminous products from bayerite to nordstrandite and/or gibbsite and then to pseudoboehmite and/or amorphous material. In the presence of anions with a great affinity for Al, particularly at pH equal to or less than 9.0, the reaction products were commonly poorly crystalline or structurally distorted. In the range of pH 8.0 to 10.0 moderately or strongly chelating anions acted to retard or prevent olation and facilitated the formation of stable pseudoboehmite or X-ray-amorphous products. The stronger the chelating power or the higher the concentration of organic anions, the easier was the formation of pseudoboehmite or amorphous material.