MINERALOGY OF SURFACE SEDIMENT IN THE EASTERN AREA OFF THE RYUKYU ISLANDS AND ITS GEOLOGICAL SIGNIFICANCE

The mineral composition of the bulk samples of the surface sediment in the eastern area off the Ryukyu Islands is studied with X-ray diffraction(XRD). It is found that the sediment consisting of smectite, illite+mica, kaolinite+chlorite, quartz, potash feldspar, plagioclase and calcite, is dominated by quartz, illite+mica, calcite and plagioclase, and kaolinite+chlorite and smectite occupy the second place with potash feldspar occasionally observed. According to the mineral composition, it is deduced that the sediment came from terrigenous, volcanic and biogenic sources.