Calcite and/or aragonite were formed from calcium bicarbonate solutions containing sodium sulfate, sodium chloride and magnesium chloride of various concentrations. Sodium, chloride and sulfate contents of synthetic calcite or aragonite were measured. Sodium and chloride ions are incorporated into aragonitic calcium carbonate more easily than into calcitic calcium carbonate, although sodium and chloride ions in the parent solution favor the formation of calcitic calcium carbonate. On the other hand, sulfate ions are incorporated into calcitic calcium carbonate more easily than into aragonitic calcium carbonate, although sulfate ions in the parent solution favor the formation of aragonitic calcium carbonate. Sodium content of aragonite, which is precipitated from calcium bicarbonate solution containing sodium sulfate, sodium chloride and magnesium chloride, exhibits a maximum value together with sulfate content of aragonite.