Solid-state transformation of amorphous calcium carbonate to aragonite captured by cryoTEM

Early stage reaction mechanisms for aragonite promoting systems are relatively unknown, compared to the more thermodynamically stable calcium carbonate polymorph, calcite. Using cryoTEM and SEM, we identified the early reaction stages taking place during aragonite formation in a highly supersaturated solution using an alcohol-water solvent, and described an overall particle attachment growth mechanism for the system. We provide the first in vitro evidence for the solid-state transformation of amorphous calcium carbonate to aragonite, demonstrating the co-existence of both amorphous and crystalline material within the same aragonite
needle. This supports non-classical formation of aragonite within botha synthetic and biological context.