During studies of CoO-CoF2 mixts. in air at 1000 Deg, incomplete drying of air established the excellent transport property of the reaction SiO2 (s) + 4HF (g) = SiF4 (g) + 2H2O (g) (1). Traces of water in the air hydrolyze CoF2 to HF which reacts with SiO2 according to (1). Then the synthesis of Co2SiO4 proceeds by SiF4 (g) + 2CoF2 (g) + 4H2O (g) = Co2SiO4 (s) + 8HF (g) (2). The HF formed in (2) may react with CoO to produce CoF2. The possibility of 2CoF2 (g) + 2SiO2 (s) = Co2SiO4 (s) + SiF4 (g) is also considered. Carrier gas methods and closed transport cycles are contemplated in the extension of this gas phase synthesis to other metals.