Two series of interstratified illite/smectite (I/S) minerals from the Shinzan, Japan, hydrothermal alteration products (100-0% of smectite layers) and the Kinnekulle, Sweden, diagenetic bentonite beds (60-30% of smectite layers) have been examined by infrared (IR) spectroscopy in the 4000-250 cm^-1 frequency range as functions of percentage of smectite layers (%S), tetrahedral Al, and octahedral Fe+Mg contents. The band shift and intensity variation in the IR spectra of the I/S series did not show an additive nature as if interstratified minerals were a simple mixture of each component layer, but showed characteristic features at each %S and for different origins in some specific bands. The Shinzan I/S series can be classified into three groups taking into account the band shift and intensity variation of IR spectra and the other mineralogical properties: one I/S with 100-50%S, the second I/S with 50-30%S, and the third I/S with 20-0%S. Such a classification may be responsible for that I/S has different basic structures of silicate layers at each %S stage. The basic structure of silicate layer in the first group of I/S is fundamentally that of smectite, the third group is that of pure illite, and the second group is an intermediate. The Kinnekulle I/S did not follow the above classification. This may be due to differences in the basic structures of silicate layers and the chemical composition between the two I/S series. The Kinnekulle I/S is more phengitic and poorly ordered than the Shinzan I/S even at a given %S.

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The rehydration properties for Ca-, Mg-, Na-and K-saturated montmorillonites after heating at various temperatures were examined and positions of interlayer cations for unheated, dehydrated and rehydrated specimens were investigated by means ofone-dimensional Fourier analysis.
Mg-saturated specimen dehydrated irreversibly after heating at 400°C, while rehydration was recognized after heating at 600°C for Ca-and Na-saturated specimens and at 700°C for K-saturated specimen. After heating at 600°C for the Na-saturated specimen, the interlayer cations (Na⁺) migrated into shallow part of the hexagonal holes, and the heated specimen restored its original hydrated configuration of interlayer region after water saturation. In the case of after heating at 800°C, the interlayer cations (Na⁺) migrated into deep part of the holes, and rehydration did not occur even after water saturation. These results are due to the fixation of interlayer cations (Na⁺) to the hexagonal holes of SiO₄ network after heating at 800°C, and it becomes difficult to extract these fixed cations from the holes. Therefore, the migrated positions of interlayer cations play an important role in its rehydration properties.

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Cobalt aluminum double hydroxides were formed by a coprecipitation method. The solid solution range of the double hydroxides was 0.20≤x≤0.32, where x=Al/(Co+Al) in the resulting products. Anion exchange capacities of the Cl-type compounds were 2.01-2.74 mequiv/g. The interlayer anions were ion-exchanged by various inorganic and organic anions, and the basal spacing increased in the following sequence;CO₃^2-<Cl^-<NO₃^-<SO₄^2-.

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The expansion-collapse characteristics of rectorites are investigated by X-raydiffraction under conditions of relative humidities, ethylene glycol and glycerol treatments and Greene-Kelly test. The expandability of rectorites is similar to that of beidellite rather than montmorillonite. The distinctive nature is shown under the conditions of 30-90% relative humidity (Na-and Ba-form), ethylene glycol treatment (K-form) and Greene-Kelly test. The difference of expandability between montmorillonite and beidellite is not observed on glycerol treatment (Mg-form). The expandabilities of the minerals are somewhat different from sample to sample. The relationships between chemical compositions and expansion characteristics are discussed.

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