The volcanic ash soils with different colours, textures and hardnesses were collected from the soil profile according to different depths in northeast Japan. The mineralogical properties of the soils were studied.
1. The soils usually have a clay pan at about 30 cm in depth from the surface, strong adhesion, and are very poor in plant growth.
2. The soils have low saturation degree, and these pH values are low.
3. The mineralogical compositions of the sand fraction is composed of quartz, oligoclase-andesine hypersthene, opaque minerals, pumice, volcanic glass and a very small amount of augite and hornblende. In the lower layer which is the weathered product of the dacitic tuff referred to upper Pliocene age, hornblende did not be found.
4. The clay fraction is mainly composed of montmorillonite with a small amount of halloysite, gibbsite, quartz, cristobalite. From the surface layer to the middle montmorillonite slightly decreases, and gibbsite and halloysite increase. In the lower layer which has a large amount of gibbsite and cristobalite, any clay minerals except a very few amount of halloysite did not be found.