鹿児島県日置郡郡山町の新第三紀安山岩における粘土化作用と蛋白石晶洞生成の関係について
1970 年 10 巻 3-4 号 p. 102-109
詳細
1970 年 10 巻 3-4 号 p. 102-109
Several sheets of intensely montmorillonitized andesite are inserted into the Miocene sediments around Koriyama-machi, Kagoshima Prefecture. They consist mainly of plagioclase phenocryst, montmorillonitized groundmass and a number of opal druse. As result of the observation under the microscope, the X-ray analysis and the chemical analysis, it is concluded that opal druses may have been formed by the precipitation of excess silica accompanying montmorillonitization of groundmass in secondary voids after pyroxine phenocryst. Most of opal druses are composed of the peripheral part, the horizontally precipitated part and the central void. And the inclination of the surface of horizontally precipitated opal is almost zero, though that of the sediments exceeds 10°. Then, this fact may suggest that the precipitation of opal may have lasted after the stage of main tectonic movement in this area.
