熊本県人吉市大塚地域の変質火山岩中の粘土鉱物

抄録

Hydrothermally altered volcanic rocks are widely distributed in the Otsuka district, Hitoyoshi City, Kumamoto Prefecture. These altered rocks can be divided into two zones based on the clay minerals contained. They are smectite zone (Zone I) and mixed-layer mineral with kaolinite zone (Zone II). Zone I is a weakly altered area characterized by existence of smectite, and Zone II is characterized by a regularly interstratified smectite/illite and kaolinite. Many specimens of mixed-layer mineral found in this area have 30-35% of smectite layer, whereas specimens of mixed-layer mineral in quartz veins and rocks affected by silicification in the Zone II have 45-50% of smectite layer. The mixed-layer mineral was probably formed from smectite under a certain hydrothermal condition.