Optical, chemical, X-ray and infrared studies on several manganoan alkali-calcic amphiboles from manganese ore deposits were performed. Optical properties are as follows: extinction angles are large (c∧X or c∧Z 30-44°) and dispersion is very strong (2 V_x=20-40° for yellowish species and 2 V_x = 30-88° for others). Al₂O₃ content is very small for the all amphiboles examined. Manganese is contained generally in smaller amounts than 2.0 per formula unit except for kozulite (3.7), and it distributes in M1·M2·M3 sites rather than in M 4 site. A site is occupied by alkali ions in vari-ous amounts. The spacing a_Osinß and cell volume increase in proportion to occupancies of alkali ions in the A site. Infrared OH stretching bands can be divided into two ranges: 3725-3680 cm^-1 and 3680-3640 cm^-1. The former bands may be shifted to the higher wave number side by the effects of alkali ions in the A site, and the intensity ratios to the latter bands are interpreted to be controlled by the A site occupancies of alkali ions. OH deformation (bending) bands appear also near 700 cm^-1 and near 600 cm^-1, and they are correlated with the oh stretching bands in a reversed frequency relation.

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Optical absorption spectra of synthetic (Ni, Mg)₂SiO₄ and (Co, Mg)₂SiO₄ olivines have been reexamined at room temperature in the near ultraviolet, visible and near infrared ranges, by the method of diffuse reflection attenuance. The samples were synthesized by sintering the pellets of NiO, MgO and SiO₂ mixture and CoO, MgO and SiO₂ mixture. Both of the spectra of the two kinds of olivines consist of three bands, which are consistent with the crystal field theory, and two kinds of bands which were assigned to transition metal in the distinct octahedra, are superposed on each three bands. The spectra of (Co, Mg)₂SiO₄ olivine series are more complicated, because two bands of high energy side are superposed on each others. High and low spin configurations of Ni²⁺ ion (3d⁸) have theoretically no difference. But it was revealed that the Co²⁺ ion in olivine has high spin state. After the assignments of these spectra, the value of Dq and Racah value B were determined as(Ni, Mg)₂SiO₄ Dq (cm^-1) B (cm^-1)M(1) 856 980M(2) 762 902(Co, Mg)₂SiO₄M(1) 940 920M(2) 720 820The excess CFSE is a few kcal/mole in M (1) site of both olivines.

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Recent advances in X-ray studies of electron-density distributions in crystals of transitionmetal compounds are reviewed. To obtain quantitative information on electronic states from the observed electron-density distributions, structure refinements are required to be carried out with orbital scatterering factors for various electron configuration models. Formulation of the orbital scattering factors are first explained, and then several examples are described. In the case of KFeF₃ with a perovskite-type structure, the spin state was unequivocally determined from X-ray diffraction data. On KCuF₃ with a Jahn-Teller distortion, mixing of the d_x²-y² and d_z² orbitals revealed. The obtained value for the degree of mixing is in coincidence with the value estimated theoretically based on the bond distances. The electron distribution around the Cu⁺ ion in CuAlO₂ showed hybridization of 3 d_z² and 4 s orbitals. The degree of hybridization was determined by the analysis with the aspherical scattering factors for the hybridized orbitals.

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Outlined principle and application of crystal-field theory have been described. Some spectral data on chromium ions constituted of diopside and larnite were interpreted on the basis of energy diagrams. Emphasis was placed on the presence of tetrahedrally coordinated low spin Cr³⁺ ions in these synthetic silicates. Following crystal-field parameters were obtained for each solid solution series in average. Characteristic colours are presented in brackets and energies of crystal field splitting (Δ) and Racah parameter (B) are represented by cm^-1. A. CaMgSi₂O₆-NaCrSi₂O₆ series (green). Δ₀=15, 160 B=726 B. CaMgSi₂O₆-CaCrCrSiO₆ series (blue). Δ_t=10, 340 B=431 C. CaMgSi₂O₆-CaCrAlSiO₆ series.C-1. High temperature series (green). Δ₀=15, 860 B=575C-2. Low temperature series (blue). Δ_t=10, 170 B=424 D. CaCaSiO₄-CaCrCrO₄ series.D-1. β, larnite-series (green). Δ_t=13, 870 B=462D-2. α-series (green), One specimen. Δ_t=13, 710 B=457Though coexistence of octahedrally coordinated high spin Cr³⁺ ions was estimated for the series of B, C-2, D-1 and D-2, octahedral parameters were scarcely determined due to superposition of spectra.

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