pH- and conductometric titration curves of acid sauconite, freshly prepared by the action of H-resin on sauconite showed four segments, each, where H+, Al3+ and Zn2+ ions and a weak acid reacted with the added base in the sequence mentioned. The H+, Al3+ and Zn2+ ions, but not the weak acid, could be exchanged for the cations of a neutral salt. The exchangeable Al3+ and Zn2+ ions were derived from the lateral surfaces by the action of the H-resin. When the acid sauconite was allowed to age in water, the exchangeable H+ and Al3+ ions were gradually replaced by Zn2+ ions giving, finally, a Zn-clay. The pH rose from 4·2 to 6·3 and the total amount of exchangeable cations increased as aging proceeded. When the Zn-clay was formed, the increase in cation exchange capacity was about 70 per cent. Octahedral Al at the edges, carrying positive charges, were discharged by hydrolysis during the aging, causing the net negative charge and, hence, cation exchange capacity, to increase. Aging had little effect on the amount of the weak acid. Zn and Al ions at the edges exhibited the weak acid function. Only edge-Zn was active in the fully aged clay.

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.

This paper documents the first report of flint clay in Mexico, located at Estola, Guerrero, 199 km south of Mexico City, on Mexico Highway 95. It is the first report (known to the writers) of flint clay formed by hydrothermal alteration. It describes the in-situ alteration of a calcareous, silty shale to flint clay (well-ordered kaolinite).

The changes during alteration are mineralogical, chemical, and structural. Calcite, comprising about one-third of the shale, quartz and probably some feldspar comprising a scant third, and a mixture of greenish-yellow (limonitic) clay minerals are dissolved or altered ultimately to white kaolinite (monomineralic). Calcium carbonate, free and combined silica, and iron compounds are dissolved, while simultaneously the alumina is relatively enriched. The fissility, inequigraularity, and cementitous fabric of shale are changed to the massively homogeneous, finegrained, interlocking fabric that is typical of flint clay.

The sequence of changes, which overlap, are; (1) dissolution of carbonate minerals, (2) mobility of iron, replacement of quartz and feldspar by kaolinite; and (3) intensive “digestion” of rock substance to homogeneous, essentially monomineralic, kaolinite flint clay. Alunite, and secondary vein-calcite or gypsum may accompany the flint clay.

This occurrence lends support to the concent that flint clay is formed from presumably only sedimentary parent rock.

Li-, Na-, K- and Ca-saturated Wyoming montmorillonites have been prepared and used to obtain Li,Na-, Li,K-, and Li,Ca-montmorillonites with a range of Li contents. These were heated at 220°C for 24 hr, causing the Li+ ions to migrate mainly into the layer structure and leaving varying amounts of Li+, Na+, K+, and Ca2+ ions in the interlayer positions as determined by exchange with NH4+ ions. The results are only partially consistent with a migration of the Li+ ions into vacant octahedral sites up to the limit of the octahedral layer charge. Solvation of the resulting clays with water and various organic liquids showed the following results: With water, acetone and 3-pentanone, expansion of the montmorillonites increased in a step-wise manner with increasing numbers of interlayer cations qualitatively in accord with the field strength of the cations and the dipole moments of the molecules. With ethanol, ethylene glycol and morpholine, swelling with each liquid was practically independent of the number of interlayer cations, within the limits of the prepared materials. It is suggested that for the second group of liquids some mechanism additional to cation-dipole interactions, such as hydrogen bonding to silicate oxygen surfaces, may play an important part.

The sorption of commercial K-Cu chlorophyllin by a sample of montmorillonite saturated with different exchange ions was studied. The organic anions are sorbed on external surfaces while K displaces most of the exchangeable cations. The samples sorb the constituents of chlorophyllin selectively and in different amounts, depending on the exchangeable cations of the clay. These also affect the amount of material peptized and the relative orientation and aggregation of the particles.

One-g samples of a montmorillonite, a metabentonite, an illite, two kaolinites, and three halloysites were treated with 50 ml of hydrochloric acid (6·45 N, 1: 1), acetic acid (4·5 N, 1: 3), sodium hydroxide (2·8N), sodium chloride solution (pH 6·10; Na = 35‰; Cl = 21·5‰), and natural sea water (pH 7·85; Na = 35·5‰; Cl = 21·5‰) for a 10-day period in stoppered plastic vials. The supernatant solutions were removed from the clay minerals and analyzed for SiO2, Al2O3, CaO, MgO, Na2O, and K2O. All the solutions removed some SiO2, Al2O3, and Fe2O3 from the samples, but the quantities were small. Sodium hydroxide attacked the kaolin group minerals more strongly than it did montmorillonite, metabentonite, or illite. Halloysite was more strongly attacked by hydrochloric acid than was any of the other experimental minerals. Hydrochloric acid removed iron oxide coatings from soil clay minerals, but acetic acid did not remove them completely. The samples most strongly attacked by HCl and NaOH were examined by X-ray diffraction. Acid treatment did not destroy the structure of the clays, but the halloysite structure was partially destroyed. Sodium hydroxide attacked the halloysite structure, as shown by chemical analysis and X-ray diffraction. These experiments show that treatment in dilute acids has no harmful effect in the preparation of clays for X-ray diffraction. Acetic acid is preferred to hydrochloric acid for this purpose. Hydrochloric acid cleans clay minerals by removing free iron oxide from the surface; acetic acid is less effective.

Previous studies of the line profiles of the basal reflections of microcrystalline muscovites were refined by an adaptation of the method developed by Maire and Méring. In order to evaluate the variation of interlayer spacings, the method required only relative values of Fourier coefficients, without the correction for instrumental broadening, which was the source of one of the most critical problems previously. Instead of Kα radiation, Kβ radiation was used to record line profiles since difficulties associated with the separation of Kα1 and Kα2 radiations could not be overcome satisfactorily.

The data reconfirmed that the line broadening of 00l reflections was due not only to a small particle-size effect, but also to structural disorders involving the variation of the interlayer spacings. For the four specimens investigated here, the mean squares of the variation of interlayer spacings ranged from 0 to 0·0358, the square roots of which were inversely proportional to the total number of interlayer cations. It is considered that the observed distortions were mainly attributed to non-uniform interlayer spaces between silicate layers arising from an irregular distribution of interlayer cations. The data also indicated that the crystallites of all four specimens consisted of a similar number of layers. The method showed promise for the study of the nature and extent of structural disorders in micas or other silicate minerals.

The hydrophilic-hydrophobic properties of four thermally decomposed organoclays, the octadecylammonium-, the dimethylaryloctadecylammonium-, and the dimethyldioctadecylammonium-bentonites and the dimethyldioctadecylammonium-hectorite, were examined through adsorption isotherms with nitrogen, water vapor, and hexane. Along with DTA and TGA results, these clay complexes appear to undergo transitions from low to higher degrees of hydrophilicity as more and more of the hydrocarbon chains are dehydrogenated at successive temperatures up to 400°C.

Sequential alteration of volcanic rock of rhyolitic composition to a precursor of endellite, and thence to tubular endellite, may be observed at a hot spring about 27 km north of Ciudad Hidalgo, Michoacan, Mexico. Ojo Caliente de Laguna Larga (or Verde) yields H2S-SO2-containing water, temperature about 45°C pH 3·5–3·7, from multiple orifices in vesicular and slabby rock with which the water reacts.

First-stage alteration of the rock consisted of permeation and dissolution, accompanied by deposition of clay substance in vesicle walls. The clay substance, although “amorphous” to X-rays, yields a weak DTA of endellite, and kaolinite. It is interpreted as a precursor of endellite. Further reaction included continued filling of vesicles and spreading argillation which coalesced between vesicles and other rock pores. Ultimately, the rock was completely “digested” to well-defined endellites.

Strong desilication and depotassication of the rock is indicated by the dissolved substances in the spring water: Si 59·1 (equivalent to 127 SiO2) ug/ml: Al, 1·63; Fe, 0·65: Mg, 0·21: Ca, 178: Na, 0·73: K, 13·7. Despite high K+, predominantly high H+ and Al3+ induce formation of endellite. The clay-water system accords well with stability diagrams.

Allophane-endellite in Indiana and endellite at Stanford, Kentucky, are formed from cold, strongly acid, meteoric-water solutions high in Si and Al relative to kaolinite dissolved in water. Factors of genesis common to both hot- and cold-water endellite are cited, suggesting that they are premissively critical, but not necessarily restrictive, to the origin of endellite.

The author regrets that in the photograph section on p. 50 the caption to the “top” Fig. 2 should read:

Fig. 2(b). Rock sample of attapulgite from Yucatan, Mexico (Tertiary).

the caption on the “bottom” Fig. 2 should read:

Fig. 2(a). Spray-dried attapulgite from Yucatan, Mexico.

Also the bar scales on Fig. 9 were inadvertently juxtapositioned:

Fig. 9(a) should carry the 10 μL scale, and Fig. 9(b) the 1 μ scale.