Expansion-collapse characteristics of interstratified chlorite-montmorillonite were compared with those of montmorillonite and vermiculite. The expansible component of interstratified chlorite-montmorillonite is neither entirely montmorillonitic nor entirely vermiculitic. It shows resistance both to expansion on glycerol solvation after Mg-saturation and to collapse on K-saturation. A model is proposed to explain these experimental results.

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Dissolution by acid oxalate solution was investigated as a means of determination and removal of allophane and iron and aluminium oxides in clays. Allophane and amorphous oxides of iron and aluminium were selectively dissolved in 0.15 M acid oxalate solution of pH 3.5 by shaking for 1 hour at 30°C or 3 hours at 20°C, provided the ratio of sample weight to solution volume was 100 mg to 200 ml. Dissolved silica was determined directly by a heteropoly blue method and aluminium and iron were determined as ferron complexes after removal of the oxalate by H₂SO₄-HNO₃ treatment. Crystalline clay minerals such as kaolinite, halloysite, metahalloysite, montmorillonite, gibbsite, hematite and goethite were hardly dissolved by the same procedure.

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A mixture of equal amounts of calcined flint clay and kaolinite was thoroughly ground (mixture 2). A 50 % alumina-silica refractory brick [HE 50 (2)] was prepared by firing this mixture. Physical and chemical properties and mineralogical composition of the ground mixture and the brick were examined. They were compared with the properties of a mixture of calcined flint clay and kaolinite of which each component was ground prior to mixing (mixture 1) and of a brick obtained from this mixture [HE 50 (1)]. Amorphous material, surface area and water sorption are higher in mixture 2 than in mixture 1. By grinding, small particles of kaolinite adhere to the larger particles. Mullitization in HE 50 (2) is greater than in HE 50 (1); this leads to a lower porosity. Differencesbetween the two bricks seem to be associated with differences between the fine structures of the two mixtures.

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Formation of interlayer complexes of 2:1 lattice type clay minerals with KC₂H₃O₂ was investigated by x-ray analysis. The basal spacing of the Na-or K-saturated montmorillonite increased from 12 A to 15 A when the increasing amounts of KC₂H₃O₂ were added and air-dried. No further expansion of the spacing occurred even if KC₂H₃O₂ was added in a greater amount. The 15 A spacing of KC₂H₃O₂-added montmorillonite contracted to 13.6 A by heating at 150-200°C, whereas the spacing of Kor Na-saturated (salt free) one contracted to 10 A. The rate of the salt addition required for the development of the 15 A spacing was 3.5 and 2 m. mols perg clay for Na-and K-saturated montmorillonites, respectively, and this difference may be correlated with the CEC value 1.2 me perg clay. It was concluded that the complex, “montmorillonite-K⁺-KC₂H₃O₂”, was formed and that KC₂H₃O₂ formed a monolayer in the interlayer region of the mineral. Vermiculite also formed a similar interlayer complex with KC₂H₃O₂, but illite and chlorite did not.

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The surface area of allophane and imogolite which had been dried over P₂O₅ in vacuo or heated at various temperatures was determined by the ethylene glycol monoethyl ether (EGME) and nitrogen (N₂) methods. The result was compared with that of montmorillonite.
A part of water adsorbed on allophane and imogolite could not be replaced by EGME, being different from water adsorbed on montmorillonite. Adsorbed water must be completely removed prior to the treatment with EGME for the determination of the surface area of allophane and imogolite. For this determination the P₂O₅ vacuum-drying of the sample was suitable but the oven-drying at 105°C was not suitable on account of the collapse of pores of these minerals. The pores collapsed by heating was, however, recovered by remoistening. Heating at 200 to 300°C increased, whereas heating at temperatures above 300 to 400°C decreased the EGME and N₂ specific-surface-areas of allophane and imogolite. The former increase was ascribed to the removal of strongly adsorbed water from the minerals, and the latter decrease to a destruction of the structure of the minerals which would result in decrease in their porosity. Infrared analysis revealed that some Si-O-Al linkages in allophane and imogolite were destroyed by heating between 300 and 400°C.

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Six specimens of sericite minerals collected from wall-rock alteration zones of the Kuroko deposits of the Hanaoka, Kosaka and Shakanai mines, Akita Prefecture, have been examined by x-ray, chemical, infrared absorption and differential thermal analyses. The results reveal that one specimen is sericite, and the other five are interstratified minerals of sericite and montmorillonite with 5 to 40 percent montmorillonite layers. Polytypes identified in the specimens are 2M₁, 1M and 1Md.
Chemically the specimens are characterized by high aluminium and low magnesium and iron contents, and have a dioctahedral structure. The slight differences in octahedral composition due to substitution of aluminium by magnesium and iron can be correlated with their polytypes: the 2M₁ type has a composition close to that of muscovite, but the 1M type is phengitic. The d(060) spacings and the vibration frequencies of the IR bands at about 530 cm^-1 also indicate these chemical variations. The differences in appearance of the endothermic peaks between 500° and 700°C of the DTA curves seem to be related to the octahedral composition.

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