It is a high honor to be invited to give this first Brindley Memorial Lecture. I view it as taking the first step on a ladder, to be followed by suceeeding talks that climb higher to the pinnacle that George Brindley erected for us in clay mineralogy. If George were with us, he would be sitting on the front row, as usual, keeping the speakers and audience "honest" in our deliberations. In turn, I would be privileged to ask him personally to enlighten us with his valued opinion on the many questions I will be asking in this talk.

13C and 29Si nuclear magnetic resonance spectroscopy with magic-angle spinning bas been used to study the short-range ordering and bonding in the structures of intercalates of kaolinite with formamide, hydrazine, dimethyl sulfoxide (DMSO), and pyridine-N-oxide (PNO). The 29Si chemical shift indicated decreasing levels of bonding interaction between the silicate layer and the intercalate in the order: kaolinite: formamide (δ) = -91.9, ppm relative to tetramethylsilane), kaolinite: hydrazine (-92.0), kaolinite: DMSO (-93.1). The 29Si signal of the kaolinite:PNO intercalate (-92.1) was unexpectedly deshielded, possibly due to the aromatic nature of PNO. The degree of three-dimensional ordering of the structures was inferred from the 29Si signal width, with the kaolinite: DMSO intercalate displaying the greatest ordering and kaolinite: hydrazine the least. 13C resonances of intercalating organic molecules were shifted downfield by as much as 3 ppm in response to increased hydrogen bonding after intercalation, and in the kaolinite: DMSO intercalate the two methyl-carbon chemical environments were non-equivalent (δ = 43.7 and 42.5).

Hydroxide and oxyhydroxide products of aluminum were formed at room temperature at an initial Al concentration of 2 × 10-3 M, pH 8.2, and at varying concentrations of organic and inorganic ligands commonly found in nature. The effectiveness of the ligands in promoting the formation of noncrystalline products over crystalline Al(OH)3 polymorphs was found to be in the following order: phthalate ≅ succinate < glutamate < aspartate < oxalate < silicate ≅ fluoride < phosphate < salicylate ≅ malate < tannate < citrate < tartrate. The lowest ligand/Al molar ratio at which the production of Al hydroxides or oxyhydroxides was inhibited ranged from 0.02 to 15. Above critical ligand/Al ratios, crystalline products were inhibited and ligands coprecipitated with noncrystalline products which remained unchanged for at least 5 months. Polydentate and large ligands generally were more inhibitive than those with fewer functional groups or of smaller size.

The perturbing ligands promoted and stabilized the formation of pseudoboehmite over crystalline Al(OH)3 polymorphs in the following sequence: chloride < sulfate < phthalate ≅ succinate < glutamate < silicate < aspartate < phosphate < salicylate ≅ malate < tannate < citrate < tartrate. The optimal range of the ligand/Al molar ratios for the formation of pseudoboehmite varied, for example, from 0.005–0.015 for tartrate to 600–1000 for chloride. Pseudoboehmite was not formed in the presence of fluoride.

Mobility measurements were made for dry-ground mica particles dispersed in aqueous KCl, Cr(NO3)3, and cetyltrimethylammonium bromide (CTAB) solutions. In the latter solutions charge reversal occurred at about 2 × 10-6 M and 3 × 10-5 M, respectively. Negative zeta potentials in KCl solutions calculated using the Smoluchowski equation are about one third of the corresponding values obtained from streaming potentials and force measurements using mica sheets. Good agreement, however, was obtained when positively charged groups created during grinding were neutralized, and the zeta potentials were corrected according to the procedure of O'Brien and White with an assumed average particle size of 0.25 μm. When the zeta potentials of positively charged particles were corrected in this way, agreement with values calculated from force measurements was also improved.

Spherical and platy kaolinite crystals were prepared under several hydrothermal conditions. Spherical kaolinite was produced mainly at high solid/water ratio (1/4) and at low temperatures (150°-200°C). Platy kaolinite predominated in products from experiments with intermediate solid/water ratios (1/256-1/16) and at high temperatures. Boehmite predominated at low solid/water ratios (1/4096) at all experimental temperatures (180°-220°C). The results indicate that the growth of the spherical kaolinite was favored at high degrees of supersaturation, whereas the growth of the platy kaolinite was favored at relatively low degrees of supersaturation.

Dehydration-induced luminescence (DIL), the emission of light from a clay paste upon dehydration, was characterized experimentally for a colloidal kaolinite. The relationship between total photon count of the emitted light and film thickness is linear up to a thickness of 30 μm. The photon emission was obtained over a critical range of water contents (25-60%) of the oven-dry clay, and the kinetics of photon emission was presumed to be closely associated with the kinetics of film dehydration. Whether drying proceeded throughout the bulk or via a moving front was undetermined, but in either mode it was preceded by the formation of a thin dry film at the interface with the atmosphere. Grinding of the kaolinite for several minutes by mortar and pestle before paste preparation resulted in an overall increase of photon emission compared to unground kaolinite and in the formation of more than one emission peak, as well as a prolongation of the light emission. This effect on the kinetics of light emittance was observed for about two months after the application of the mechanical stress and suggests a means of detecting the mechanical stress history of a clay.

An estimate was made of the spectral characteristics of the emitted light using optical filters and by incorporating tryptophan and salicylic acid into the kaolinite paste where they acted as fluorescent probes. The latter technique shifted the frequency of the light emitted by the kaolinite from the ultraviolet to the visible range where it was less effectively reabsorbed. The first method showed that the wavelengths of 97% of the emitted light was <460 nm and that 75% of the light had wavelengths <410 nm. The second method showed that the total intensity of DIL increased in the presence of fluorescence molecules, suggesting that the emittance was in the ultraviolet range.

Oxygen isotope analyses (δO18) of micas that were artificially depleted in K+ indicate little or no isotope exchange during the transformation. The oxidation of iron in K-depleted, iron-rich micas by H2O2 treatment resulted in 1.6 to 4.6% decrease in SO18 due to the fact that the equilibrium fractionation factor is less than the initial difference between the starting δO18 of the fluid and micas. The oxygen isotope ratio of a saponite formed by the weathering of phlogopite showed a 9.7% increase in δO18 due to authigenic recrystallization. These results suggest that oxygen isotope ratios can be used to determine the nature of chemical transformation during the weathering of mica to vermiculite and/or smectite.

The transformation of ferrihydrite to goethite and hematite in the pH range 9–13 is retarded by the presence of simple sugars (>- 10-4 M concentration). The retarding effect is related to the extent of adsorption of the sugar on ferrihydrite. Maltose and glucose adsorb strongly and inhibit the transformation by preventing both aggregation and dissolution of the ferrihydrite. Sucrose adsorbs to a much lesser extent than the other sugars and appears to hinder the nucleation and growth of goethite in solution.

Hematite formation relative to that of goethite is favored by the sugars in the order: maltose >glucose ≫ sucrose. Maltose and glucose cause hematite to grow as prismatic crystals rather than as hexagonal plates and also lead to a new type of twinned goethite; one with epitaxial outgrowths of goethite on a prismatic crystal of hematite. In alkaline media glucose and maltose are partly transformed into a mixture of different sugars and hydroxycarboxylic acids, and it is probable that modification of the hematite crystal shape is due to the presence of the degradation products rather than to the nature of the original sugar.

The results of this work suggest that cyclic molecules influence the transformation of ferrihydrite to a lesser extent than do acyclic molecules.

Transmission and analytical electron microscopy have been used to study the diagenesis of the trioctahedral component of phyllosilicates (principally chlorite) in argillaceous core samples (depths of 1750, 2450, and 5500 m) from the Gulf Coast. Chlorite was observed as 100-150-Å thick packets intergrown within mixed-layer illite/smectite in the 2450-m sample and was more abundant and larger in packet thickness in the 5500-m sample. The chlorite is disordered in stacking sequence as characterized by diffuseness of reflections with k ≠ 3n in electron diffraction patterns. Berthierine (7-Å) was locally found to be intercalated within chlorite layers. Chlorite from the 5500-m sample is iron-rich and has an average chemical formula of Fe3.1Mg1.1Al2.7Si2.8O10(OH)8. This chemical composition and textural relations suggest that the chlorite formed within mixed-layer illite/smectite utilizing Fe and Mg released from the smectite during its conversion to illite. The berthierine is nearly identical in chemical composition with the coexisting chlorite although it may have a slightly higher Fe content. The 7-Å berthierine is probably a metastable precursor of the chlorite and may be diagnostic of the diagenetic environment.

Small-angle X-ray powder diffraction analyses and high-resolution electron microscopy of allophane samples (SiO2/Al2O3 ratio, 1.12 to 1.68) showed that allophanes consist of nearly identical spherical particles with diameters of about 40 Å and retain their characteristic “hollow” spherical morphology at different ambient moisture and even after dehydroxylation by heating at 500° to 600°C. Unheated allophane samples gave another X-ray powder diffraction band whose maximum position varied from 12.3 to 14.5 A depending on their SiO2/Al2O3 ratio. The appearance of this band may denote some long-range ordering in the structure of allophane. Unlike the spherical particles of allophane, the tube unit of imogolite collapsed on dehydroxylation. This observation suggests that imogolite and allophane are different in their framework structures and that a Si- or Si(Al)-tetrahedral sheet rather than an Al-octahedral sheet constitutes the framework structure of allophane, irrespective of its SiO2/Al2O3 ratio.

To test the double-layer theory of swelling as applied to layer silicates, the interlayer separation, λ, in a Li-saturated vermiculite from Grouse Creek, Utah, was measured as a function of the swelling pressure, II. An oriented sample of the vermiculite (46-105 μm) was placed in an environmental chamber mounted on an X-ray diffractometer and compressed between N2 gas and a porous membrane in contact with a solution draining to the outside atmosphere. After equilibration at each of several successively higher gas pressures, the c-axis spacing was measured by X-ray diffraction, and the corresponding X was calculated by subtracting the thickness of an elementary silicate layer. The results of these measurements showed that. (1) the relation between II and λ for vermiculite is the same as that previously observed for Na-montmorillonite, i.e., II is an exponential function of 1/λ. (2) the values of II predicted by double-layer theory are much smaller than those observed if the surface potential is assigned the appropriate value; an. (3) the observed relation between II and λ does not have the form predicted by this theory. On the basis of these results, a repulsive force not ascribable to double-layer overlap must be primarily responsible for swelling; this force must result from the in-depth perturbation of the water by the surfaces of the vermiculite layers.

Ion-exchange sites with very high selectivity for Cs ($\mathrm{\Delta }{\mathrm{G}}_{{\mathrm{C}\mathrm{a}}^{2+}}^{{\mathrm{C}\mathrm{s}}^{+}}$ = 40 kJ/eq) similar to illite were generated in a controlled way in montmorillonites b. (1) repeated wetting-drying cycles and b. (2) charge reduction using the Hofmann-Klemen effect. An almost continuous range of sites with selectivities varying from ln ${\mathrm{K}}_{{\mathrm{C}\mathrm{a}}^{2+}}^{{\mathrm{C}\mathrm{s}}^{+}}$ = 33 to 5 was observed.