Shape-constraint as a route to calcite single crystals with complex morphologies

Sponge-like polymer membranes, formed by templating sea urchin skeletal plates, were used as an environment in which to precipitate calcium carbonate. Using double diffusion conditions and under a specific range of reagent concentrations single crystals of calcite with sponge-like morphologies were precipitated, whose form was dictated by the confines of the polymer membrane. Investigation of the mechanism of formation of these particles showed that both templated calcite and vaterite particles nucleated at early times, but that the proportion of vaterite present decreased with time due to dissolution and reprecipitation as calcite. All evidence suggests that the templated calcite single crystals grew in the absence of an amorphous calcium carbonate (ACC) precursor phase, demonstrating that the presence of ACC is not a necessary prerequisite to the formation of single crystals of calcite with complex morphologies.