Thermal transformation of chrysotile from Uruaçu District, state of Goiás, Brazil, heated in dry conditions at temperatures from 600°C to 1300°C was studied by high resolution electron microscopy and selected area electron diffraction (SAD). Up to 600°C, no morphological or SAD pattern changes were observed. At 600°C, the fibrils were still crystalline with the characteristics of the clinochrysotile. In addition, a new fringe system of 10–15 Å spacings appeared sporadically parallel to the 7.3 Å fringes of chrysotile. Areas of these extra fringes seem to constitute favorable sites for the nucleation of forsterite. At 650°C, forsterite nuclei appeared inside the nearly amorphous fibrils in the shape of patches consisting of flaky crystallites. At 700°C the chrysotile structure had disappeared; the new spots present in the SAD pattern were indexed as those of forsterite. Between 800–900°C the crystallinity of the patches was clearly demonstrated. From the lattice images in the patches, topotactic relations between chrysotile and forsterite were analyzed. At 1000°C very tiny grains of enstatite were formed mixed with forsterite grains. The SAD pattern is complex due to the coexistence of forsterite, enstatite, and silica-rich amorphous areas. From 1100°C to 1300°C the tridimensional growth of enstatite was promoted. The present results support the topotactic relations between chrysotile and forsterite found by X-ray analysis although differences up to several degrees may exist when these phases are observed microscopically. Evidence suggesting a topotactic growth between forsterite and enstatite was also obtained.

The addition of a 10% talc internal standard to North Pacific sediments allows the relative abundances of clay minerals to be determined both accurately and precisely by X-ray powder diffractometry. Linear programming can be used to generate factors for converting talc-normalized peak areas to weight percentages; hence, absolute clay-mineral abundances can be estimated. This procedure minimizes residuals (nondiffracting or poorly crystalline components), but its accuracy is untested. Even this procedure results in an average residual of almost 30% for North Pacific sediments; other peak-area to weight conversion schemes generate even larger values.

In general, there is no correlation between clay-mineral abundances estimated from talc-normalized peak areas and abundances derived from the assumption that the sum of smectite, illite, kaolinite, and chlorite is 100%. This accounts for the past difficulties in relating bulk-sediment chemistry to clay mineralogy.

Clay minerals in the upper 50 cm of sediment that surround the Cu- and Ni-rich manganese nodules in the North Equatorial Pacific form two fractions: terrigenous (mostly eolian) illite, chlorite, and kaolinite, and authigenic smectite. Smectite increases with depth in box cores from 26 to 39% and from 53 to 66% in the easternmost and westernmost areas respectively, and with distance seaward from the Americas from 26 to 53% in surface deposits. The change in the amount of smectite relative to other clay minerals is due to dilution by terrigenous debris; smectite probably forms at a uniform rate over much of the North Pacific deep-sea floor. The δO18 value for the smectite is +29.6‰ which suggests that it formed authigenically at a temperature characteristic of the deep-sea floor. The smectite is an Fe-rich montmorillonite that probably forms by the low-temperature chemical combination of Fe hydroxides and silica. Silica is derived from dissolution of biogenic debris, and the Fe hydroxide is from volcanic activity at the East Pacific Rise, 4000 to 5000 km to the east. Al in the authigenic montmorillonite may be derived from the dissolution of large amounts of biogenic silica or from river-derived Al that is adsorbed on Fe-Mn hydroxides in the oceans. The Fe-montmorillonite contains relatively abundant Cu, Zn, and Mn and is of possible economic importance as a source of these and other metals.

Ferrihydrite was transformed to goethite and/or hematite at various temperatures, [OH], and [Al]. Increasing temperature and [Al] favored hematite, increasing [OH] favored goethite. A given [Al] induces hematite more effectively at lower [OH]. Al substitution in goethites increased linearly with log[Al], but was independent of temperature. At a given [Al], substitution increased with decreasing [OH]. In a plot of Al/Fe in the goethite against [Al]/[Fe(OH)4−] in solution a straight line was obtained for all preparations independent of [OH].

When aqueous dispersions of Na+-smectite or n-butylammonium-vermiculite react with sulfate salts of Fe(II), Co(II), or Ni(II) bipyridyl or 1, 10-phenanthroline complexes in excess of the cation-exchange capacities, intersalated phases with spacings of about 29.5 Å are obtained. Thermal decomposition of the intersalated complex cations affords expanded phases with a d(001) spacing near 18 Å for the smectites and near 28 Å for the vermiculites. These phases are stable to temperatures of at least 550°C. Nitrogen surface areas of the fired products are as high as 400 m2/g.

Imogolite occurs as tiny bumps less than 0.05 µm in diameter and about 0.3 µm long on amorphous thin layers on the surface of weathered plagioclase. The bumps grow outward from the surface to form projections, which then develop into a fibrous imogolite. The fibers branch out and grow into widespread networks or thin films which finally cover the entire surface of the plagioclase grain. The fibers are about 0.05 µm in diameter as seen by transmission electron microscopy.

The hydroxyl orientations in 31 dioctahedral and trioctahedral 2:1 phyllosilicate structures have been determined by electrostatic energy calculations. These structures included micas, brittle micas, and other related minerals exhibiting ordered as well as disordered cation distributions. The dioctahedral micas and brittle micas were examined with and without the interlayer cation. A range of orientations from 1.3° to 183.3° (the angle ρ between the O-H and (001) measured with respect to the M1 site) were found. The orientations for the dioctahedral structures represent a continuum of values whereas the trioctahedral species exhibit two possible orientations separated by an energy barrier. One orientation is near 90° the other is near 180°. The latter orientation results from a concentration of charge on the interlayer (IC) and tetrahedral (T) sites at the expense of the octahedral (M) sites. A multiple regression analysis of all 31 structures, using as predictors the a and b cell parameters, d001, and the charges for T, IC, M1, and M2 sites, was performed. This analysis indicated that the important factors are the charges for IC, T, and M2 sites. When treated as a separate group, one finds the same factors for the dioctahedral structures. The trioctahedral orientations are determined by the charge on the M2 site and the amount of tetrahedral rotation. Using these two predictor equations, the value of ρ can be estimated with a standard deviation of 4.7° and 2.9° for the dioctahedral and trioctahedral cases, respectively.

The roles of different forms of Fe(III) impurities in a hectorite with respect to the oxidation of benzidine in aqueous suspension have been evaluated using electron spin resonance and UV-visible spectroscopy. Natural surface-adsorbed Fe(III) showed no detectable activity in the oxidation process, while very small quantities of structural octahedral Fe(III) apparently promoted a relatively rapid conversion to the radical cation. However, extremely small quantities of benzidine were oxidized in comparison to the exchange capacity of the clay. Freshly adsorbed Fe3+ cations effectively oxidized benzidine, but lost much of this ability upon aging. The Fe(III)-benzidine electron transfer could be distinguished from an O2-benzidine reaction, since the latter reaction was slow and limited by the rate of O2 diffusion into the clay-water system. The O2-benzidine reaction was also inhibited at high pH. The existence of two reaction mechanisms and the involvement of only a small fraction of the total structural iron, as shown by comparison of the hectorite and a montmorillonite, may explain the conflicting interpretations in the literature. The benzidine blue reaction not only requires an oxidizing agent to form the radical, but also a clay surface to adsorb and stabilize it against further oxidation.

Natural erionite was exhaustively ion exchanged with Na+ to give the anhydrous unit-cell composition (K1.9Na5.4Ca0.1Mg0.1)[(AlO2)7.4(SiO2)28.6]. A thermodynamic study of alkali and alkaline earth metal ion exchange in this zeolite was made and the selectivity series found to be Rb > Cs ≥ K > Ba > Sr > Ca > Na > Li. In all cases approximately two K+ ions per unit cell (probably those in the cancrinite cages) could not be replaced by conventional ion exchange. It was also found that two Na+ ions per unit cell are extremely difficult to replace with alkaline earth ions. It is believed that complete replacement of the approximately six Na+ cations in the two large cages per unit cell of erionite would result in a non-uniform, divalent cation population in these cages. A more stable anhydrous composition is (K2Ca2Na2)[(AlO2)8(SiO2)28] in which each large cage contains one Ca2* or other alkaline earth cation and one Na+ ion.