The original igneous rocks of weakly metamorphosed greenstones are basalt-dolerite and limburgite in Mikabu Green Rocks of the Ogose area, and basalt-dolerite-bostonite and limburgite in the Chichibu melange zone of the Agano area, both of Kanto Mountains. Relict phenocrystic clinopyroxenes of basaltic and limburgitic rocks of both areas are chromian augite (Cr₂O₃ 0.4-0.8 wt.%) to chrome augite (Cr₂O₃ more than 0.8 wt.%), but, in general, comparatively poor in TiO₂ (less than 0.1 wt.%). However, limburgitic pyroxenes of the Chichibu melange zone are slightly richer in TiO₂ and Cr₂O₃ and higher in Mg/(Fe+Mg) than those of the Mikabu rocks. The phenocrystic clinopyroxenes are generally similar in Cr₂O₃/TiO₂ ratios to clinopyroxenes of ocean-floor basalts and of peridotite xenoliths derived from the mantle.

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A digital image processing system composed of personal computer, TV camera and image digitizing board, was developed for the analysis of optical properties of ore minerals under the microscope. The system can quantitatively carry out surface, line and point analyses of brightness and chromaticities in minerals.
Under reflected light, chromaticities of electrum were measured using the system. Good correlations were observed between Ag contents and chromaticities. Brightness and chromaticities of sphalerite with color zoning was also measured under transmitted light. They suggest that the color in sphalerite changes from pale yellow to orange with increase of Sb and Cd contents. This method is applicable for various studies on mineral textures.

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The gallium content of 21 plutonic rocks of the Miocene ring complex of the Cape Ashizuri, Kohchi Prefecture, Southwest Japan, has been determined by X-ray fluorescence spectrometry. From the correlation of gallium with the previously reported aluminium data, we have suggested two contrastive trends of differentiation, high-Ga trend and low-Ga trend. The former trend was operative during the evolution of the cogenetic syenitic rocks, i.e., melanocratic syenite→quartz yenite→alkali granite→quartz syenite porphyry, all of which occur in the inner zone of the ring complex. The Ga values are almost constant or slightly increasing (23 to 27 ppm) but in the last stage increase abruptly up to 33 ppm in the quartz syenite porphyry having the characteristics of a residue of syenitic magma. In contrast, the latter trend is exhibited by gabbroic rocks, coarse-grained quartz syenite, rapakivi granite and coarse-grained biotite granite occurring in the outer zone of the complex, and the Ga values slightly decrease from 23 to 15 ppm as the Al₂O₃ content decreases.
The qualitative analyses revealed that the gallium has been concentrated mainly in La-Ce-Nb-F minerals in the quartz syenite porphyry. The rocks on the high-Ga trend have higher fluorine content than those on the low-Ga trend, and the Ga/Al ratio of some A-type granitoids in the world shows a positive correlation with fluorine content. These data indicate that the two differentiation trends of the Ashizuri plutonic rocks have been caused by the difference of fluorine content in the magma.

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Dark-brown micro-minerals scattering in the wine red part of lava-coated anorthite megacryst, from the island of Miyakejima, were identified as native copper by using the conventional EPMA equipment and the enhanced X-ray microdiffractometer of a new type developed by the authors. Tiny lamellae of these native coppers are distributed on ( ?? 04) of anorthite. Their chemical compositions are near pure copper metal, whereas the anorthite around their coppers is slightly rich in silica and contains a small amount of chlorine. Comparison with the X-ray CuLα and CuLβ spectra, measured by EPMA, of native and metallic coppers, and cuprite and tenorite, brings out that the peak shift and band shape of CuLα radiation from this Cu inclusion agree well with those of native and metallic coppers. The present microscopical investigation implies that after exsolution of the H₃CuSi₃O₈ feldspar endmember possibly forming a solid solution of the primary anorthite, decomposition of this Cu-bearing feldspar in the process of descent temperature conduces to yielding native coppers and the anorthite slightly rich in SiO₂. The present paragenesis of euhedral anorthite megacrysts including native coppers with fused olivines asserts that there is some high temperature region (>1400°C) underneath Miyakejima, namely beneath a volcanic front and over the subduction zone, where such an idiosyncratic anorthite can crystallize.

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A middle Miocene alkali dolerite was found on Rebun Island in the northeastern part of the Japan Sea. It has ophitic texture and consists of plagioclase laths, titaniferous augite and ilmenite. Chemically, this dolerite is characterized by high Na₂O, TiO₂, P₂O₅ and Fe₂O₃. The K-Ar age of this rock is 18.2±1.2 Ma, suggesting alkaline basaltic magmatism took place during the formation of the Japan Sea.

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