The growth of calcite spherulites from solution: II. Kinetics of formation

The reaction rate of calcite sphere formation was investigated. Samples of precipitates and solutions were taken at various times and characterized for morphology, phase, chemistry, and pH. It appears that the Mg 2+ and SO 2− 4 impurities have a controlling influence on both the phase and morphological development of precipitates. The calcite spheres initially precipitate as an amorphous phase, and then go through a transition into a rough intermediate spherulitic morphology before the final development into near-perfect spheres. Slower crystallization and a diffusion-controlling boundary layer of rejected impurities apparently is part of the mechanism controlling spherical growth.