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Precipitation of Calcium Carbonate in Confinement

In contrast to the regular morphologies displayed by synthetic single crystals, biogenic single crystals frequently exhibit unusual forms and curved surfaces. Such controlled mineralization in biology occurs within restricted volumes constructed for this purpose and there is significant evidence that some crystals with complex morphologies may form via an amorphous precursor phase. We here investigate morphological control of single crystals, using these biological mechanisms as inspiration. Calcite was precipitated within the cylindrical pores of track‐etch membranes via an amorphous calcium carbonate (ACC) precursor phase. Perfect replication of the pore channel to yield rod‐shaped single crystals of calcite was only achieved when the ACC precursor particles entirely filled the pore channels prior to crystallization, a process dependent on the pore diameter. Misshapen particles were formed in all pore diameters in the absence of an ACC phase. This system provides an ideal opportunity to carry out a systematic study into the effect of pore diameter, and the presence of an ACC precursor phase on crystal growth.