Calcite spherulites have been observed in many laboratory experiments with different bacteria, and spherulitic growth has received much interest in mineralogy research. However, the nucleation and growth mechanism, as well as geological significance of calcite spherulites in solution with bacteria is still unclear. Herein, spherulites composed of an amorphous core, a Mg-calcite body and an organic film were precipitated by the Curvibacter lanceolatus HJ-1 bacterial strain in a solution with a molar Mg/Ca ratio of 3. Based on the results, we provide a possible mechanism for the biomineralization of Mg-calcite spherulites. First, amorphous calcium carbonate particles are deposited and aggregated into a stable sphere-like core in combination with organic molecules. The core then acts as the nucleus of spherulitic radial growth. Finally, the organic film grows on the surface of Mg-calcite spherulites as a result of bacterial metabolism and calcification. These findings provide insight into the growth mode and crystallization of biogenic spherulites during biomineralization, and are of significance in the application of novel biological materials.

The spherulitic and lamellar morphologies of melt crystallized isotactic polypropylene (iPP) have been investigated according to various crystallization temperatures and times. In this study, an appropriate chemical etching condition for the observation of iPP morphology by scanning electron microscopy (SEM) is determined. The optimum etchant formulation is 3 wt% potassium permanganate with the mixed solvent of sulfuric acid and phosphoric acid. The morphologies after etching reveal the microstructure of iPP clearly, such as the characterization of α/β spherulites and the different lamellar growth patterns.