Stabilisation of Aragonite: The Role of Mg2+ and Other Impurity Ions

Aragonite formation and stabilisation in seawater is still an area of active investigation since the thermodynamically stable product at room temperature is calcite. In this manuscript, purely inorganic systems that were found to stabilise aragonite were analysed by various techniques. Dynamic Light Scattering was used to characterise the nucleation behaviour of the system and it was found that the presence of magnesium ions during crystal formation inhibits nucleation overall, not just calcite nucleation. In addition, it was found that sulfate is not necessary to stabilise aragonite. Microanalysis by energy dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) revealed that the aragonite that was formed had a disordered core with, sodium, magnesium and sulfate ions incorporated into the structure. To the best of the authors’ knowledge this is the first time an ACC core in aragonite has been visualised in a completely abiotic, synthetic system (in the absence of organic molecules). Inclusion of these impurities into the structure may explain the stability of aragonite in natural seawaters.