From the symmetry point of view, micas may be classified as follows: those with all three octahedrally coordinated sites occupied by the same cation (homo-octahedral micas), those with only two of these sites occupied by the same cation (meso-octahedral micas), and those with the three sites occupied by different cations or by two different cations and a void, in an ordered manner (hetero-octahedral micas). For any of these three classes, mica polytypes, idealized in accordance with the generalized Pauling model, can be interpreted as OD structures consisting of octahedral OD layering and tetrahedral OD layering in which an interlayer cation plane is sandwiched between tetrahedral sheets. A mica layer built up by an octahedral sheet and two halves of tetrahedral sheets on either side consists of two OD packets linked by a two-fold rotation.

The orientation of any OD packet may be given by a number from 0 to 5 (related to a hexagonal coordinate system). A dot behind or before these numbers is used to denote the position of the octahedral layer (number + dot = orientational character). The displacement of a packet against its predecessor is characterized by a vector from the origin of a packet pn (or qn-1) to the origin of the adjacent packet pn+1 (or p2n). These displacements may also be symbolized by numbers from 0 to 5 (displacement characters); a zero displacement is symbolized by *. Any mica polytype (ordered or disordered) can thus be described by a two-line symbol. The orientational characters are located on the first line, and the displacement characters on the second. Any symbol, therefore denotes unequivocally the stacking layers in a polytype. The space-group symmetry of ordered polytypes follows directly from the symbol.

The specific conductivity, κg, of Na/Ca montmorillonite gels (0.02 and 0.04 g clay/cm3) as a function of the specific conductivity of the interclay solution, κw, was measured. For low values of κw (<3 mmho/cm) the conductivity curves were convex with respect to xw; at higher values they were linear. The κw at which deviation from linearity began increased with increasing sodium content from 0.7 mmho/cm for the Ca-montmorillonite gel to 2.6 mmho/cm for Na-montmorillonite gel. The intercept of the linear portion of the conductivity curve increased and its slope decreased with increasing exchangeable sodium. The experimental results were described by a conductance model comprised of two elements connected in parallel: an element consisting of the solid and solution phases connected in series, and another consisting of the solution phase. At low electrolyte concentrations, the first element accounts for the curvature of the κg-κw curve, whereas at high electrolyte concentrations, the second element dominates, and the curve is linear with a slope determined by a formation factor and an intercept determined by exchangeable cation mobility.

An adjustable parameter in the conductivity term for the first element, which accounts for the thickness of the clay particles, increased with exchangeable Na, and its numerical value indicated that the solid phase also includes the diffuse double layer. The mobility of the exchangeable cation relative to that in water increased from 4% for Ca to 41% for Na with the largest increase occurring between 20 and 40% exchangeable Na. Similar effects of exchangeable Na were evident on the axial ratio of the clay particles calculated from the slopes of the linear lines. These observations are consistent with an exchangeable-ion demixing model where the initial exchangeable Na is adsorbed on the external surfaces of the Ca-montmorillonite tactoids without affecting exchangeable ion mobility or tactoid size. Further additions of exchangeable Na result in Na adsorption on the internal surfaces of the tactoid and tactoid breakdown with a subsequent increase in both exchangeable ion mobility and the axial ratio of the clay particles.

A standardless method of energy dispersive X-ray fluorescence in conjunction with scanning electron microscopy was used to analyze selected areas of clay-size particles of talc, pyrophyllite, and kaolinite supported by a carbon planchet. Peak intensity ratios of fluorescing elements relative to silicon were converted directly to weight or mole ratios using conversion factors determined theoretically. The conversion factors depend upon particle thickness and mass adsorption coefficients of the sample for the elements analyzed. The effects of particle thickness become significant above ~0.1 μm. Without using particle thickness corrections, the mean molar ratios of metal to Si agreed to within 6.1,0.5, and 9.7% of the theoretical ratios for kaolinite, pyrophyllite, and talc, respectively.

Uranyl acetatye solutions, ranging in concentration from about 100 ppm to 3700 ppm, were re-acted with the Na-, K-, and Ca- forms of zeolite A. The crystalline products from the Na- and K-A zeolites resembled compreignacite (K2O·6UO3·11H2O) and from the Ca-A, becquerelite (CaO·6UO3·11H2O). With higher concentrations of uranyl acetate, only X-ray-amorphous products were obtained. The compreignacite-like products gave sharp X-ray powder diffraction patterns and were indexed with orthorhombic, quasi-hexagonal unit cells which showed a significant variation of the axial ratio b/a from values just greater than, to values just less than √3. The becquerelite-like phase was always accompanied by unreacted zeolite. Compreignacite was synthesized from uranyl acetate and KOH solutions at room temperature over a period of several days.

The Mössbauer effect of Fe57 was used to probe and characterize iron ions adsorbed on the interlayer surfaces of montmorillonite. Measurements were performed with Fe- and Ca-saturated mont-morillonites. At 210°K the intensity of the Fe2+ line was greatly reduced, apparently due to the melting of interlayer water. Neither the structural Fe2+ in Ca-montmorillonite nor the adsorbed Fe3+ in Fe-mont-morillonite were affected by the melting process. From the temperature dependence of the absorption intensity, the effective Debye temperature of all the iron species appears to be approximately the same (θD = 189 ± 5°K). This result allowed for an accurate determination of the population of Fe2+/Fe3+ in various samples.

A combination of X-ray diffraction, infrared, and chemical data has established that the ion exchange of vermiculite with singly charged benzidine cations in an aqueous solution at pH 1.6 results in a black, highly ordered benzidine-vermiculite intercalate. The intercalate has a basal spacing of 19.25 Å and a primitive unit cell with “a” and “b” edges parallel and equal to those of vermiculite. The number of benzidine molecules per cell is equal to its electric charge. In this structure the benzidine molecules are steeply inclined to the silicate surfaces and close-packed within domains. The domains contain alternating rows of benzidine cations; from row to row the planes are either approximately parallel or perpendicular to the (120) plane, but along any one row the planes of the aromatic rings are parallel to each other. Hydrogen bonding operates between amine nitrogens and surface oxygens.

The broad charge heterogeneity typical of nearly all smectites is not necessarily characteristic of vermiculites. In addition to vermiculites with pronounced heterogeneity, minerals with no or only limited charge heterogeneities are known. Layer charge and charge heterogeneity of 25 vermiculites were determined by alkylammonium ion exchange. The comparison of experimental basal spacings with dL/n-plots provided a simple determination of the average charge density. The spacings of high-charged vermiculites (≥0.8 eq/(Si,Al)4O10) with paraffin-type interlayers follow a straight line in the dL/n-plots. Lower-charged vermiculites were recognized by stepwise increasing spacings due to mono-, two-, or three-layer chain packings. Charge heterogeneity produced a superposition of the dL/n-curves for different charges, and the basal reflections of some of the alkylammonium derivatives became nonintegral.

The adsorption of sodium, chloride, and phosphate ions by allophane, imogolite, and halloysite has been studied in relation to the surface structure of the mineral samples. The high adsorption of phosphate (>200 μmole/g) and chloride (10–30 meq/100 g at pH 4) by allophane is ascribed to the small particle size of allophane, its high surface area (∼800 m2/g), and the presence at the surface of Al-OH-Al groups and defect sites. In contrast, halloysite has a relatively large particle size and a Si-O-Si surface. Accordingly, the adsorption of phosphate (5–10 μmole/g) and chloride (1 meq/100 g) by halloysite is very much lower as compared with allophane. Phosphate adsorption by halloysite is also related to particle morphology and the number of edge sites. Thus, a sample consisting entirely of spheroidal particles adsorbed only 5 μmole/g at a solution concentration of 1 × 10−4 M, whereas the tubular types of comparable surface area adsorbed 7–10 μmole/g at the same concentration. This is because spheroidal halloysite particles have few, if any, edge sites at which phosphate can adsorb. The relative degree of order and hydration of halloysite, as indicated by infrared spectroscopy, also affects phosphate adsorption. However, this factor is apparently less important than particle morphology and surface structure. Although imogolite also has an Al-OH-Al surface, it contains relatively few defect sites where phosphate can adsorb. Consequently, much less phosphate (120 μmole/g) was adsorbed as compared with allophane.

Methane solubilities at 25°C were measured at 350, 550, and 750 psia in dilute (< 11 wt. %) clay slurries of Na-montmorillonites and argillaceous sediment. Methane solubilities were not significantly affected by the presence of clay. Water hydrated onto the external clay surfaces did not appear to exclude methane. In addition there was no detectable sorption of methane onto the clays. The measured solubilities are consistent with an open structure of the water hydrated onto the clay surface for which the partial molal volume is larger than that of normal water. The results imply that aqueous methane solubilities measured in the laboratory can be used to determine degrees of methane saturation in interstitial solutions in unconsolidated sediments.

An electrostatic model for the stability of clay tactoids (stacks of parallel clay platelets at ~10 Å separation) in an aqueous solution has been developed. The counter ions located in the interstitial water layers are assumed to be in equilibrium with the bulk solution. Generally, the counter-ion charge density is slightly different in magnitude from the platelet charge density. Approximating the discrete charges by homogeneously charged planes, a one-dimensional potential distribution can be calculated. From this the Gibbs energy of electrostatic interaction (using single platelets as a reference) can be computed. The model predicts that clay minerals with high (vermiculite, mica) and low (pyrophyllite, talc) degrees of cationic substitution form stable tactoids. For smectites, charge density, electrolyte concentration, and counterion species determine the swelling characteristics. At a particular charge density, lower valences of the counter ions and lower electrolyte concentrations lead to increased swelling. If tactoids are formed, the number of platelets is governed by a dynamic equilibrium between electrostatic forces, van der Waals forces, and external forces, such as shear forces due to hydrodynamic flow.

The hydrolysis and decomposition of M-hectorite (M being Na, Li, Mg, or Ca) in dilute solutions of M-chlorides were studied by recording the changes in electrical conductivity (EC) of the clay suspensions with time, and by chemical analyses of the interclay solutions and resulting solid phases. The rate of hydrolysis of the hectorites in suspension, as evaluated by the change of EC with time, was found to decrease with increase in salt concentration (to zero for Na-hectorite in NaCl concentration of 47 meq/liter), and to decrease with increase in the valency of the adsorbed cation (the rate of hydrolysis of Ca-hectorite was one sixth of that of Na-hectorite). The rate of Na-hectorite hydrolysis was determined by the concentration of protons at the clay surface as calculated from the diffuse double layer theory.

Conversely, in suspensions of Al-hectorite saturated with Na, the hydrolysis rates were not dependent on the electrolyte concentrations. This result can be explained by assuming that the hydroxy-Al polymers at the clay surface determine the proton concentration at the clay surface. Hectorites saturated with structural cations (such as Mg and Li) are chemically more stable than those saturated with Na and Ca. The presence of Li and Mg at the clay surface slowed down the diffusion release of these octahedral ions to the clay surface, compared with Na and Ca hectorite, respectively.

Adsorption and catalytic decomposition of 4-nitrobenzenesulphonylmethylcarbamate (herbicide Nisulam) on Upton, Wyoming, bentonite saturated with different cations was studied using thin-layer chromatography and infrared spectroscopy. Nisulam is adsorbed at room temperature by coordination through the NO2 group to the exchange cation regardless of the cation's nature. On moderate heating (75°–90°C) this molecule decomposes to 4-nitrobenzenesulphonamide whereas a similar compound (herbicide Asulam) containing the NH2 functional group instead of NO2 is adsorbed by protonation at room temperature and decomposes into different products. For cations having a high polarizing power, a coordination bond between the Asulam molecule's C=O group and the exchange cation is established, and the molecule decomposes to sulphanilic and carbamic acid. In contrast, for cations having a low polarizing power there is no coordination, and the molecule decomposes mainly into sulphanilamide. Nisulam's coordination to the exchange cation through the NO2 group instead of C=O is ascribed to inductive and conjugation effects, typical of the nitro group.