Little attention has been paid to the reaction of mixed calcium-iron carbonate in solutions in comparison with the reaction of other solids such as calcium carbonate, calcium sulfate and barium sulfate. As a result, little information is presently available about the interaction and precipitation of iron carbonate; and mixed calcium/iron. It is known that iron carbonate precipitation kinetics is sensitive to temperature. At high temperature (65 °C), a sharp drop in iron concentration was observed during the first minutes in a solution devoid of calcium. And the drop was gradual at 55 °C. However, adding calcium to the solution under the same conditions had a great influence in reducing the drop in iron concentration. The apperant increases in the solubility of ferrous iron was proportional to the concentration of calcium present in the solution. In addition, presence of calcium in solution also reduced the effect of temperature on siderite precipitation. On the other hand, the presence of iron did not show significant impact in the solubility of calcium. The cumulative molar ratio of ferrous iron to calcium in the precipitated solid was found to be varied based on the amount of siderite that initially precipitated. The X-ray diffraction analysis showed that the presence of ferrous iron inhibited the growth of calcite but did not prevent the formation of aragonite. The crystal shape of siderite, showed by scanning electron microscope, was completely different from that of calcite and the crystal shape of the solid collected in the co-existence of ferrous iron and calcium varied based on the molar ratio of iron to calcium in the solution.