Naturally occurring and biomimetic synthesized calcite spherulites

Abstract

Naturally occurring calcite spherulitic particles were collected from East Kirkton Quarry in Bathgate, Scotland. Their microstructure has been revealed, by using XRD, EDX, SEM and HRTEM, to consist of a low crystallinity core with deposition of multilayer radially oriented calcite microrods. The sur-rounding materials of the spherulites are mainly Ca-free silicates. To understand the formation mechanism of this construction of calcite crystals, biomimetic synthesis of similar spherulites have been carried out by using alginate and stevensite as structure directing agents. It is found that algi-nate is essential for growth of the spherulites, since the spherulites are developed only when they are embedded in the alginate network, a soft matter substrate. Stevensite also plays an important role of adjusting the hardness of the alginate substrate, offering a suitable network for the self-aggregation and self-orientation of the calcite nanocrystals. Possible inter-particle interactions or driving force of the particle aggregation and self-orientation are discussed.