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 forma tion 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.

(1) There are some differences in the mode of coprecipitation of phosphate ions with calcium carbonate formed from calcium bicarbonate solution between stirring and non-stirring (keeping still) the solution as follows: The amount of phosphate ions coprecipitated with calcium carbonate is larger when stirred than when kept still. In the keeping still system the amount of phosphate ions coprecipitated with calcite is approximately equal to that with aragonite, whereas in the stirring system the amount increases with increasing proportion of aragonite in calcium carbonate formed.

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