Experimental studies on olivine dissolution and ion exchange reaction were performed to understand reaction mechanism and kinetics. In the dissolution experiments, olivine crystals (Fo91) were water treated at 25°C under different pH conditions. X-ray photoelectron spectroscopy and resonant nuclear reaction analysis revealed the different characteristic features of the surface layer with the thickness of 10 to 20 nm depending on pH. The rate controlling step seems to be Si detachment under low pH conditions and Mg detachment under high pH conditions respectively. The ion exchange experiments between olivine (Fo91) and FeCl₂ solution were carried out at 600 to 800°C, 1 kb. Scanning electron microscopic observation and chemical analysis showed that the reaction front advances with precipitation/dissolution mechanism.