Siliceous hard shales, which were found from the Gamanosawa Formation of Tertiary age, Aomori Prefecture, Japan, are mostly composed of opal-CT. The name of the opal-CT rock is used here instead of the hard shale. The content of SiO₂ is in the range of 83 to 94 wt %. Broad diffused X-ray diffraction patterns correspond to the peaks of opal-CT. The spacing of 4 Å peak is in the range of 4.10 Å to 4.11 Å. Bulk density is in the range of 0.90 to 1.25, and apparent porosity in the range of 40 to 60 volume %. Crystallinity of the opal-CT rock is too poor to reveal phase transition. However, when it is heated over 1250°C in air, the crystallinity is improved and reveal phase transition at temperatures ranging from 182°C to 220°C. The spacing of 4 Å peak progressively decreased from 4.11 Å to 4.05 Å by heating it at high temperatures. By hydrothermal treatments at 500°C and 1000 kg/cm² in a high pressure vessel, the spacing of 4 Å peak also decreased from 4.11 Aring; to 4.05 Å, and opal-CT gradually transformed into quartz. The opal-CT rocks may be a transitional stage from opal-CT to quartz due to diagenesis in nature.

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Native iron has commonly been found in the serpentine vein of the second stage of serpentinization of dunites from the ultramafic masses in the Sanbagawa belt, central Japan. It is nearly pure iron but contains small amounts of Ni and Co. In the dunites other metallic minerals and sulfides have not yet been found, though magnetite and primary chromite are present. In serpentinized wehrlites from the same masses native iron is almost absent, but in a few of them native cobalt-iron, CoFe₂, which is chemically different from wairauite (CoFe), has been found. In the serpentinized wehrlites awaruite and native copper have also been found with sulfides such as pyrrhotite and pentlandite, and oxides such as magnetite and primary chromite. An occurrence of ilvaite and andradite in the serpentinized wehrlites has been noted. The chemical composition and occurrence of these minerals are described. These native metals have been formed during the serpentinization of the dunites and wehrlites.

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Hydrothermal rock alteration in the eastern Hachimantai geothermal area including Toshichi, Matsukawa and Kakkonda, Iwate Prefecture can be divided into two types; alkaline and acidic alteration types.
The alkaline alteration type characterized by the presence of chlorite associated with sericite and mixed-layer mineral of sericite and montmorillonite regionally occurs along the valley of the Kakkonda River including the Kakkonda geothermal field (hot water field). The distribution area of sericitic minerals within the area of this type probably shows the upflow area of hydrothermal solutions.
The acidic alteration type characterized by minerals such as pyrophyllite, alunite and kaolinite with sudoite, tosudite, dickite, sericite, zunyite and diaspore are developed in the Matsukawa geothermal field (vapor-dominated field) which is located only 7km northeast of the Kakkonda geothermal field. The hydrothermal systems in the Kakkonda and Matsukawa geothermal fields appear to be derived from the same deep-seated hot water beneath this area.
The Toshichi geothermal field which is covered by kaolinite and alunite zones is estimated to be of a hot water system because alkaline alteration zone is developed beneath this field.

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From the Senzai vein of the Oe mine situated in southwestern Hokkaido, some kinds of rhodochrosite stalagmites are sometimes found out at the bottom of druse within the vein. The stalagmites show the shape of column, 2 to 30mm in diameter and 1 to 12cm in length. They consist of irregular fan-shaped crystals superficially and show the solution growth textures such as concentric bandings. These stalagmites have the chemical compositions of 53 to 89 mole % MnCO₃, 2 to 20 mole % CaCO₃. 7 to 26 mole % FeCO₃ and 1 to 9 mole % MgCO₃, which are mostly within the compositional region of drusy rhodochrosite of the vein. Chemical compositions of the rhodochrosite stalagmites change markedly with the concentric bands as shown in Fig. 7, which shows considerable increase of MnCO₃ content from core to rim. This feature is considered as being due to chemical changes of the ore solution or ground water producing the rhodochrosite stalagmite.

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The Tertiary igenous rocks from the Cape of Ashizuri constitute a small (about 15 kilometers in diameter) ring-like complex occurring in the Shimanto Belt (Mesozoic to Tertiary accretionary terrane), Outer Zone of Southwest Japan. They are composed of five stages of rocks, I (gabbro and dolerite), II (melanocratic syenite to alkali granite), III (coarse-grained syenitic rock and rapakivi granite), IV (coarse- to medium-grained biotite granite) and V (alkali dolerite and syenite porphyry), and characterized by alkalic to midalkalic chemistry. Comparing with the average chemical composition of Japanese granitic rocks (Aramaki et al., 1972), the igneous rocks from the Cape of Ashizuri are highly rich in (Na₂O+K₂O), while poor in CaO and Al₂O₃. In addition, F-analysis indicates exceedingly high content of 600 to 4000 ppm in most of the rocks, attaining to 7000 ppm in syenite porphyry.
Above-described facts together with some mineralogical data indicating the relatively low H₂O fugacity and low to medium oxygen fugacity, suggest the similarity of these igneous rocks with A-type granites (Loiselle and Wones, 1979) which are commonly generated along the rift zone or within stable continental blocks. The reason why the A-type granitic rocks are found within the compressional accretionary terrane has not been made clear and needs further detailed investigation.

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