Rounded pebble of metamorphosed iron-formations from conglomerate of the Miocene deposits in Yatakayama, Kibi Plateau, Okayama Prefecture

The Kibi Plateau was a part of the Eurasian Continent and separated by the event of opening of Japan Sea. The rounded pebble which is considered to be continental origin was discovered. The pebble is siliceous and attracts magnets. Prepared thin-sections were observed under microscope. Selected minerals were analyzed by EPMA. The rock is composed of recrystallized quartz, magnetite, riebeckite, stilpnomelane and associated with very tiny minerals with very high relief and interference colors. The assemblage suggests that there is a possibility that the rock is a metamorphic rock of iron-formations and derived from continent.