A hydrotalcite-type layered double hydroxide Al₂Li (OH)₆ [Fe (CN)₆] _1/4·nH₂O (Fe (CN)₆-LDH) was synthesized by a coprecipitation method and its thermal change under oxidizing and reducing atmospheres were investigated. The synthesized Fe (CN)₆-LDH consisted of plate shaped particles of 0.1-0.2μm in size and the lattice parameters were those of a hexagonal cell with a=5.06 and c=31.92Å. The interlayer spacing between the LDH octahedral layers was estimated to be 5.8Å and was occupied by 0.25 [Fe (CN)₆] ^4- anions and 1.8H₂O as the above chemical formula. The [Fe (CN)₆] ^4- anions in the interlayers were octahedral in structure and oriented with their individual 3-fold axes perpendicular to the LDH layers. The specific surface area measured by the BET method using N₂ gas as the adsorbate was 108.9m²/g. The Fe (CN) ₆-LDH decomposed upon firing up to 260°C and changed into LiAl₅O₈ and Li₂CO₃, and finally into LiAl5O8 and α-LiAlO₂ at higher temperatures. For sample fired under an oxidizing atmosphere of flowing dry air the Fe component in the Fe (CN)₆-LDH incorporated into LiAl₅O₈ by substituting for Al atoms whereas it segregated and dispersed in the samples as fine particles by firing under a reducing atmosphere of flowing H₂ gas. The resulting particles were γ-Fe₂O₃ in the samples fired at temperatures between 450° and 490°C and α-Fe above 500°C. The γ-Fe₂O₃ particles were several nm in size but increased rapidly upon elevating the firing temperature, up to submicron meter in α-Fe particles.

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Observation of the pyrophyllites from Nakamuraguchi and Takinotani under SEM showed typical particles morphology and sizes in the range of 0.1-1μm in thickness and several μm in diameter. Chemical analyses conducted with the use of WDS spectrometers proved classical pyrophyllite composition, with minor admixture of Fe. By IR method location of Fe³⁺ in octahedra has been confirmed.
Based on the diffraction patterns it was demonstrated that pyrophyllite from Nakamuraguchi mainly consists of the monoclinic form whereas pyrophyllite from Takinotani consists of mixture up to 20% of the triclinic form.
X-ray diffraction patterns from powdered samples, displayed sharp basal and subfamily reflections and strongly blurred polytypic reflections indicating a significant structural disorder. Transmission diffraction patterns from non-powdered needlelike aggregate displayed in addition the basal reflections of a series d₀₀₁·l=18.4Å. They are due to the superstructure where d₀₀₁ spacing is double of the spacing of pyrophyllite. Simulated pattern for the superstructure displayed d_00l·l=18.4Å series of basal reflections also a reflection 111 at 4.16Å of similar intensity to the one in experimental pattern. A mixture of 70% superstructure, 25% of monoclinic and 5% of triclinic structure gives the best match to the experimental diffractogram of pyrophyllite from Nakamuraguchi and Takinotani. Evidently these pyrophyllites have complex composition in which apart of domains built up of triclinic one layer per unit cell arrangement the important role plays layer pairing. Two-layer domains are created in which all layers have similar composition or every second layer has different electron density. In that latter case superstructure is observed.

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The smectite conversion can be divided into diagenesis and low degree hydrothermal metamorphism stages in the Nanatani formation (depth: 4250-6300m; middle Miocene) basalt and interstratified rocks in the Niigata sedimentary basin, Japan. In the diagenesis stage, the features of smectite conversion are crystallization and recrystallization from glass or primary minerals, precipitation as fillings of vesicle and crevice in basaltic rocks. In the low grade hydrothermal metamorphism stage, the prior smectites are dissolved and recrystallized as corrensite on the early hydrothermal progression and as chlorite and talc associated with epidote, prehnite and others on the late hydrothermal progression.
The thin section, XRD, SEM, TEM, EDS and bulk rock chemical analysis have documented that the mixed-layer Chl/S conversion from smectite to chlorite via corrensite is a discontinuous transformation process between diagenesis and low degree hydrothermal metamorphism. Although smectite and randomly mixed-layer Chl/S exhibit crystal growth from fine to coarse size in diagenetic process, the chlorite layer percentage has been only slightly changed in the mixed-layer Chl/S (chl, <15%). The low grade hydrothermal metamorphic corrensites are close to ideal 1:1 interstratified structure of mixed-layer Chl/S (chl, 45-60%) and the discrete chlorites contain a little smectite layers (chl, >90%).
The Al₂O₃-FeO-MgO relation and ratio of octahedral Fe/Fe+Mg indicate that the smectite and precipitated chlorite composition are controlled by host rocks and environmental fluid in diagenesis. However the hydrothermal corrensite and chlorite have similar compositions to those in other hydrothermal metamorphism.

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Photochemical isomerization of p-aminoazobenzene intercalated in the interlayer spaces of swelling fluor-tetrasilicic micas (TSM) was investigated. Long chain alkylammonium ion exchanged TSMs were used as the host materials to obtain hydrophobic interlayer spaces for the azo-dyes. Intercalation compounds were obtained by the solid-solid reactions between the organoammonium-TSMs and p-aminoazobenzene or p-dimethylaminoazobenzene. The intercalated azo dyes showed reversible photochromic reactions by UV irradiation and subsequent thermal treatment. The hydrophobic interlayer spaces of the alkylammonium-silicates were proved to be attractive reaction media for the immobilization and photochemical isomerization of the azo dye.

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The weathering process of a granitic rock was mineralogically investigated with XRD, XRF, SEM and TEM at one weathered profile (Ca. 20m in height) in the western part of Cameroon where climate is the intermediate of humid and arid tropical condition. Halloysite and kaolinite are main constituent clay minerals in the granite saprolite (weathered granite). Halloysite predominantly occurs at the lower part of the investigated profile associating with small amount of kaolinite. Numerous spherical-shaped halloysite were observed in the bottom of the profile under TEM. The granite saprolite at the top part of the profile consists mainly of platy kaolinite with small amount of tubular halloysite.
Detailed observation of morphological variation by TEM together with X-ray analysis revealed that the spherical-shaped halloysite crystals (0.05-0.5μm) are first unrolled and then transform to tubular halloysite (0.05-2μm), and finally unrolled again producing platy kaolinite (0.2-3μm). Close relationship between crystal size and morphology is obtained.

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Substitution of Mg²⁺ with Cu²⁺ in a fibrous clay mineral sepiolite having intracrystalline tunnels has been studied in aqueous solutions of CuSO₄ and Cu (CH₃COO) ₂. Anisotropic spectra of ESR showed that the Mg²⁺ ions on the tunnel wall in sepiolite crystal lattice were substituted with Cu²⁺ ions. The initial Cu²⁺-substitution rate in aqueous solution of CuSO₄ increased with an increase of the concentration of Cu²⁺ ions. On the other hand, the initial substitution rate in aqueous solutions of Cu (CH₃COO) ₂ was independent of the concentration of Cu²⁺ ions. The Cu2²⁺-substitution rate in CuSO₄ solution was faster than that in Cu (CH₃COO) ₂ solution. Apparent activation energies for the Mg²⁺ ion-substitution of sepiolite with Cu²⁺ were determined to be 21.2 kJ/mol and 19.4 kJ/mol in the CuSO₄ and Cu (CH₃COO) ₂ solutions, respectively.

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Quantitative estimation of clay minerals in the clay fractions of the surface sediment samples from South Yatsushiro Kai is obtained from the X-ray diffraction patterns of the clay mineral suite that contains illite, chlorite, kaolinite, smectite and 10Å halloysite. Among the clay species, illite and chlorite are exceptionally abundant and they comprise more than 60% of the total clay minerals present in most sediments. Relative amounts of other clay minerals varies markedly with locality particularly kaolinite and 10Å halloysite and they tend to concentrate only near the point source except smectite which has a more unique behavior of transport and settling characteristics than other minerals.
The relatively high supply of land-derived materials from various rock lithology surrounding South Yatsushiro Kai is the dominant contributing factor in outlining the trend of clay mineral distribution. Most, if not all, clay minerals are believed to be current-transported which shows that bottom water flow and shallow water currents are significant agents responsible for the distribution of various clay minerals.

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