Particle size distribution, minerals and chemical composition of red soils from silicate rock area of Central Okinawa

摘要

The study was conducted to determine the characteristic of Kunigami mahji from central part of Okinawa Island. The samples were collected from Gushikawa recreation center (GRC) and nearby Royalgolf (RG). Particle size distribution, mineralogy of clay, silt and fine sand and chemical composition experiments were carried out. The influence of soil erosion to amend distribution of particles and soluble cations was observed in surface sample from GRC. Pure, intergrade and irregular mixed layer minerals were found. In RG sample even in fine sand clay minerals were observed. We assumed that weathering have proceeded more in GRC than in RG sample. This is also supported by the difference of their chemical compositions. The ratios of oxides of soluble cations (alkalis and alkaline earth) to that of insoluble (Al, Fe and Si) were very higher for RG (0.042) than for GRC (0.011). Chlorite widely appeared in RG sample and only once as vermiculite-chlorite intergrade mineral in GRC, hence suggests that samples were formed from different parent materials.