Abstract
The paper presents a radiokinetic study on the appearance and growth of *Fe2S3 *Fe(OH)(3), *Fe-2(C2O4)(3), *Fe(IO3)(3) crystals in a colloidal medium of agar and gelatine. The values of the diffusion constants through gels of Fe-55+59(3+) radioactive cations and of the rate of global growth process of these crystals in agar or gelatine were calculated using the experimental data. A new method for the determination of the starting time for the complex nucleation process was proposed. The formation rate of crystals under study decreases in the order: *Fe(OH)(3)>*Fe(IO3)(3)>*Fe2S3>*Fe-2(C2O4)(3), in agar medium and *Fe(OH)(3)>*Fe(IO3)(3)>*FeC2O4)(3)>*FeS3, in gelatine medium.