Altered volcanic rocks are distributed in the Kuwanokizuru area, Hitoyoshi City, Kumamoto Prefecture. Constituent minerals in the altered rocks are smectite, mixed-layered mica/smectite, mixed-layered chlorite/smectite, chlorite, kaolinite, pyrite, quartz and α-cristobalite. Distribution of clay minerals in this area could be divided into two zones, mixed-layered mica/ smectite zone and smectite zone. In the mixed-layered zone, mixed-layered mica/smectite having high % of mica is present at two places. Furthermore, smectite % of this mixed-layered mica/smectite decreases and its Reichweite changes from 1 to 3, from the margin toward these places.
