The precipitation and dissolution processes of the iron phosphate system may be of particular interest for the mechanism of phosphorus binding in the soils. The system of Fe(NO3)(3)-H-3 PO4-H2O was investigated at pH 2.00 and 25 degrees C. At high supersaturations a crystalline phase of the Formula Fe(H2PO4)(HPO4) . xH(2)O forms spontaneously at rates strongly dependent on the solution supersaturation. The solubility product of the spontaneously precipitating phase was found. Seeding of stable supersaturated solutions with the spontaneously precipitating solid resulted in ferric phosphate dihydrate overgrowth, with a second-order dependence of the rate on the relative solution supersaturation, suggesting a surface diffusion - controlled mechanism.