In the nearly 2000 occurrences of zeolites in sedimentary rocks of volcanic origin about 15 zeolite minerals have been identified. The mode of occurrence of six of these, clinoptilolite, erionite, chabazite, phillipsite, analcime, and mordenite, is described, and their morphology is illustrated with scanning electron micrographs.

A semi-micro quantity (10-15 mg) sample of clay is pressed into a 3 mm diameter pellet for differential thermal analysis (DTA) in a STONE-TRACOR ring microsample holder. The pellet is transferred to the sample holder dish with a vacuum tweezers. Platinum sample dishes are also handled by vacuum tweezers to avoid denting the dishes or damaging the thermocouple wires. The DTA curves obtained by the pellet method are highly reproducible. The resolution and sensitivity of reaction peaks are equivalent to or better than those produced by a large sample (200 mg) packed into a nickel block holder.

Dolomite or calcite, quartz and kaolinite in various proportions were reacted at 250–300°C temperatures and pressures up to 90 bars in a hydrous environment. Reactions which approached completion produced talc, calcite, montmorillonite, anorthite (both metastable hexagonal and stable triclinic polymorphs) and the rare Ca-zeolite, garronite. These reactions are applicable to diagenesis, low-grade metamorphism and hydrothermal alteration.

The trimethylsilyl derivative from halloysite was prepared by the reaction of halloysite powder with a trimethylsilylating reagent. The product was organophilic and the results of its infrared spectrum, X-ray powder diffraction pattern, and elemental analysis indicated that the trimethylsilylation occurred on silanol groups in the tetrahedral layer of halloysite after the acid decomposition of the octahedral layer. The thermal stability of the product was evaluated by means of differential thermal analysis. It was not possible to obtain the organic derivative from kaolinite by the same procedure. It is suggested that the differences in the reactivity between halloysite and kaolinite is due to the difference in susceptibility of the clay minerals to acid attack.

The Tang dynasty is the only period of Chinese history to which the word ‘cosmopolitan’ is now routinely applied in Western-language historical writing. This article traces the origins of this glamorous image of the Tang to the 1950s and 1960s, but also links its current popularity to a more recent increase in the appeal of the concept of cosmopolitanism, as well as the idea of a ‘cosmopolitan empire’ among Western intellectuals since the end of the Cold War. The article then proposes a less presentist and more critical and holistic reading of Tang ‘cosmopolitanism’ as part of a larger, interconnected, multi-centred, and changing medieval world of numerous coexisting cosmopolitanisms, and argues for recognizing the existence of a different but equally important mode of ‘cosmopolitanism’ in the Song.

An experimentally determined Ca-Mg exchange isotherm of montmorillonite is reported. The selectivity coefficient of this exchange over a wide range of Mg saturation was calculated and found constant.

Standard free energies of exchange, thermodynamic equilibrium constants and activity coefficients of the exchangeable Ca and Mg ions in vermiculite and montmorillonite, were predicted from knowledge of the microstructure of these two clays, assuming that coulombic forces are the main ones playing a role in the interaction between the counterions and the charged clay surface. The standard free energies of exchange (ΔGCa°Mg = 238 cal/mole) predicted a preference for Ca in montmorillonite and a preference for Mg in vermiculite (ΔGCa°Mg = - 1665 cal/mole). The predicted thermodynamic equilibrium constants were compatible with the experimentally determined selectivity coefficients KsCaMg = 0·67 as compared with KsCaMg = 0·68 in montmorillonite, which remains constant over all the range of Mg saturation, and KCaMg = 16·7 as compared with KsCaMg = 13·9 in vermiculite at 95% Mg saturation. The activity coefficients of Ca and Mg counterions in montmorillonite were found to be and , respectively, and to remain constant. The activity coefficients of exchangeable Ca and Mg in vermiculite were found to be and , respectively, at an equivalent fraction of unity. The activity coefficient of exchangeable Mg increased as the saturation with Mg decreased, and was found to be 1·7 × 10-3 in the range of the low Mg saturation.

The microstructure, the isomorphic substitution and the surface charge density provided an understanding of the changes taking place in the activity coefficients of the counterions.

Mössbauer and i.r. spectra of a series of nontronites show that Fe3+ and Al3+ are distributed between tetrahedral and octahedral sites. The Mössbauer results have reaffirmed the occupation by Fe3+ of octahedral sites at which these ions are coordinated to pairs of OH groups in both cis and trans configurations. The distribution of Fe3+ between these two sites varies considerably but in all of the nontronites some Fe3+ occurs in the trans site in contrast to the all cis occupancy of the centro-symmetric structure proposed by Mering and Oberlin (1967). In one of the nontronites the distribution of Fe3+ between these two sites approaches that in the ideal non-centrosymmetric structure proposed for montmorillonite.

Electron optical observations on Marblehead illite showed the presence of twinned aggregates of lath-shaped crystallites. The selected area diffraction patterns of these aggregates indicate a strict orientational relationship between them.

Original twinned mica flakes display all possible stages of the transformation of these micas into lath-shaped illites, where the a and b dimensions of layers do not show any noticeable changes, but c-dimension becomes shortened in the illites. The transformation seems to involve parting along (110) of the micas, subsequent H2O and OH inclusion in the structure and other possible chemical changes resulting from the hydration. The morphology and the size of lath-shaped crystallites displaying (001) and (110) forms seem to be responsible for the excess of water and K-deficiency in the Marblehead illite compared to the micas.

Individual illite laths commonly have a length 0·1–4 μ, a width of 0·01–0·1 μ and a thickness varying between 10 and 50 Å.

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.

Hexafluorotitanic acid (H2TiF6) selectively dissolves kaolinite and most other phyllosilicate minerals of soils and sediments, concentrating free crystalline (Ti,Fe)O2 minerals (partially substituted anatase and rutile) in the residue. A series of H2TiF6 reagents was standardized by analysis of the Ti content and by tests with pure anatase and commercial kaolinites. The Ti in the H2TiF6 solution selected (made from 49% HF + reagent TiO2) was 16·5% by weight as analyzed by the Tiron method. Treatment of pure anatase with the reagent H2TiF6 resulted in a 98% by weight recovery of TiO2 in the residue. The fraction of TiO2 recovered in the residue of commercial Georgia kaolinites was 88–101% after treatment with the selected H2TiF6 reagent. Isolates from nine Georgia kaolinite samples with varying amounts of TiO2 and Fe2O3 were examined by X-ray powder diffraction, scanning electron microscopy and elemental analysis. The main constituent of the (Ti,Fe)O2 isolates was anatase for all samples, with minor amounts of coarser rutile and mica from coarser kaolinite. The anatase and rutile isolates contained 74–93% (Ti,Fe)O2 with 0·5–3·1% Fe. The other constituents of the isolates were muscovite of mica (0·3–7%), quartz (0–9%) and amorphous relics of vermiculite and/or kaolinite (6–19%). Rutile, muscovite and quartz appear to be detrital but the anatase and relics are probably authigenic. Fine anatase appears to stick on the muscovite flakes as revealed by scanning electron microscopy and heavy liquid data for separation of these two minerals. The (Ti,Fe)O2 isolates from kaolinites which passed with the first magnetic concentrate of anatase were coarse, on the order of a few microns dia., as revealed by the scanning electron microscopy. Those passed with subsequent extensive magnetic concentrates from the same samples were finer. The anatase isolated from kaolinite purified by removal of as much of the impurities as possible by magnetic means was extremely fine, most of the particles being on the order of 0·1 µm dia. More than one third of the total Fe2O3 in kaolinites magnetically separated in the first pass was extracted by the citrate-bicarbonate-dithionite treatment after hot NaOH dissolution of 52–74% of the kaolinite, showing that the Fe2O3 had been mainly associated within the kaolinite. Only 2–6% of the total Fe2O3 was extracted from magnetically purified kaolinite after 40–50% of this kaolinite had been dissolved, indicating that most of the Fe is in the anatase and rutile fraction.

The cell dimensions and compositions of four chlorites whose crystal structures have been determined in detail are used to test existing graphs and regression equations designed to give tetrahedral and octahedral compositions. It is found that the thicknesses of the tetrahedral sheet, the 2:1 octahedral sheet, the interlayer sheet, and the space between the 2:1 layer and the interlayer can vary appreciably from specimen to specimen quite independently of tetrahedral composition. Total octahedral composition, the number of octahedral vacancies, cation ordering, and the distribution of trivalent cations and of charge between the two octahedral sheets must have effects on d(001) that are additional to the effect of tetrahedral composition. Nevertheless, Brindley’s d(001) graph and a regression equation by Kepezhinskas both should give tetrahedral compositions with an average error of 10%, or about 0·1 AlIV, for most trioctahedral chlorites. They are not valid for dioctahedral or di, trioctahedral species. Equations derived from the data of von Engelhardt and of Shirozu relating the b parameter to octahedral Fe, Mn content give results with an average error of 10%, or 0·1 Fe, Mn, for the four test chlorites provided Cr is included with the Fe, Mn, as does a regression equation by Kepezhinskas that contains terms for both the b parameter and d(001). Methods using the (00l) intensities or structure amplitudes give less consistent results for heavy atom contents than the spacing methods, but can be used to give approximate values for the asymmetry in distribution of heavy atoms between the 2:1 octahedral sheet and the interlayer.