Phyllosilicates are major components of the <2-μm fraction (1–3 wt. % of most bulk specimens) in more than 50 samples of air-fall tephra from several 1980 eruptions of Mount St. Helens. In all samples, trioctahedral smectite is the major clay mineral. The integral series of 00ℓ reflections in ethylene glycol-treated samples indicates a lack of interstratification; absence of a peak near 5 Å after heat treatment, the 060 peak at 1.54 Å, and energy dispersive chemical analyses indicate that the smectite is a Mg- and Fe- rich, trioctahedral saponite. Minor mica and chlorite are present in the <2-μm fraction of most samples, and some samples show a peak near 12 Å after heating to 550°C which is probably due to the presence of an interstratifled chlorite/collapsed smectite or chlorite/collapsed vermiculite. The tephra contains glass and crystals originating from new magma and lithic fragments incorporated from the pre-existing cone. The clay minerals in the tephra are lithic components stripped from older, hydrothermally altered rocks during explosive ejection. Cleaned pumice fragments, which are new magmatic components, lack smectite, but contain rare biotite in xenoliths. Old, hydrothermally altered rocks from the volcano's summit and from the debris-avalanche (former north flank) contain saponite together with chlorite and chlorite/smectite which may have formed from it. Saponite and zeolites that precipitated from neutral to alkaline hydrothermal solutions line cavities in some of these rocks. The saponite was probably not subjected to magmatic temperatures because heating this material for 5 min at 750°C collapses it irreversibly to 10 Å. Kaolinite, alunite, and opal, indicative of acid-sulfate alteration, were found only in the pre-1980 summit crater and the southwest thermal area, but were not evident in the lithic components of the 1980 deposits.

Alteration products of andesite cobbles from wet soils formed in volcanic colluvial material were studied using petrographic, electron microscope, X-ray powder diffraction, and thermal techniques. Augite phenocrysts altered by congruent dissolution leaving voids which were subsequently filled with smectite. Plagioclase also altered to produce micrometer-size spheroidal aggregates of smectite. Halloysite was not observed within the altered cobbles, although it was abundant in the soil matrix. The formation of smectite in the altered cobbles was probably favored by the restrictive drainage of the microenvironment in combination with wet soil conditions.

Berthierine (formerly chamosite) occurs as concretions, lenses, and bands in carbonaceous, kaolinitic shale of freshwater coal-swamp deposits in Paleogene and Upper Triassic coal measures of Japan. Textural relations in thin sections of the Triassic berthierine rocks and a siderite-kaolinite-berthierine-quartz assemblage in Paleogene rocks indicate that the berthierine formed by reaction of siderite with kaolinite. The transformation of siderite and kaolinite to berthierine and quartz occurs progressively under reducing conditions between 65° and 150°C and at burial depths of 2–5 km. Utatsu berthierine is an aluminous, low-Mg variety as compared with berthierine pellets in modern marine and estuarine sediments and in ancient marine ironstones. Fe is the dominant octahedral cation with Fe2+ ≫ Fe3+. The composition of the berthierine varies between different morphological types. Utatsu berthierine transformed to ferrous chamosite when kaolinite in the host shale changed to pyrophyllite. These transformations are estimated to have occurred at ∼160°C and at a burial depth of ∼3 km.

Clayey sediments of marine origin having sensitivities (ratio of undisturbed to remolded shear strength) as high as 1000 at a reduced salt concentration are found around Ariake Bay, Kyushu, Japan. The clay fraction of the sediments contains smectite as a principal mineral (33–42%) in contrast to the illitic composition of most previously described quick-clays. However, this smectite is a low-swelling type, and the Na-form expands only to about the same extent as the Ca-form and gives a sediment volume almost equal to that of the Ca-clay. This low-swelling smectite appears to consist of packets of unit layers even after saturation with Na, and thus reacts like the kaolinite or illite of conventional quick-clays.

The solubility of four different gibbsite preparations was measured, including two commercial hydrated aluminas produced by Alcoa, a Fisher ACS-grade Al(OH)3, and a laboratory preparation. The Alcoa samples and the laboratory-prepared sample had been studied previously by other investigators but without using a long-term acid treatment. Scanning electron microscopy showed globular surface material that was removed by a 14-day, 0.1 M HCl treatment. Solubility was determined at pH 4 from both over-and undersaturation with continuous agitation for 228 days. The acid treatment correlated with a decrease in log*Kso[*KSO = (Al3+)/(H+)3] of about 0.5 units. The mean solubility of the three acid-treated commercial gibbsite samples was log*Kso = 7.55 ± 0.055 (*Kso = 3.5 × 107). The solubility of the acid-treated laboratory preparation was log*Kso = 7.86 (*Kso = 7.2 × 107). The greater solubility of the laboratory-prepared gibbsite is attributed to a greater concentration of structural defects in the crystals.

The ferrous iron content of two vermiculitized biotites decreased by treatment with 0.1 N salts of copper at 70°C from 9.1–14% to 1.8–2.6%. Presumably, interlayer copper ions acted as a catalyst (here, an electron carrier) for the oxidation of iron by dissolved oxygen. The oxidized iron was ejected from the structure and formed crystalline iron minerals, such as hematite and goethite. Weight loss determinations, chemical, and X-ray powder diffraction data suggest that Cu(II) ions were polymerized to hydroxy-hydrous compounds in the interlayer space. Poor exchangeability of the resultant complex is attributed to the formation of strong electrostatic attractions between OH groups of the interlayer complexes and silicate oxygens.

Clay/electrolyte systems are best characterized using a new variable, notional interfacial content (NIC). The NIC approach emphasizes that any division of the total amount of a species present in a clay/electrolyte system into that part which ‘belongs’ to the clay and that part which ‘belongs’ to solution is necessarily arbitrary. It carries out this division by choosing one of the species as a reference species and defining it as being completely in a notional bulk solution which had the same composition, but not extent, as the real bulk solution. The NIC of each of the other species present, that is that part of their total amount not in the notional bulk solution, therefore represents the amounts of those species ‘belonging’ to the clay.

The NIC concept is universal and hence encompasses several other, older terms. For example, by choosing different reference species, the variables hitherto called ‘water adsorption’ and ‘negative adsorption’ (which have been used to describe the same phenomenon) may be obtained. Similarly, certain earlier definitions of exchangeable and adsorbed cations (some being pragmatic are not included) as well as that of ion surface excesses may be accounted for. The NIC approach thus provides a rationalization of several earlier terms which are, in fact, plagued by a multiplicity of definition which makes their use very complicated.

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.

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.