The production of Fe 2 SiO 4 (fayalite) crystalline grains was performed by two processes, namely, grain formation in a plasma field by evaporating a mixture powder of Fe and SiO and heat treatment of the product collected on the radio-frequency (RF) electrode side. Fe grains <20nm in size covered with an amorphous SiO layer selectively formed Fe 2 SiO 4 grains by heating at 800°C. By heating at 600°C, in addition to the formation of Fe 2 SiO 4 crystal grains, the FeO phase appeared. The doping effect of excited oxygen in a plasma field into the Fe small grains may be the trigger on the formation of fayalite through the FeO phase formation. The present experimental result suggests that the probability of Fe 2 SiO 4 grain formation in space is low.