Aragonite crystals with unconventional morphologies

Abstract

Conventionally, the aragonite polymorph of CaCO₃ possesses a ‘needle-like’ morphology. Aragonite crystals with unconventional morphologies, like ‘cauliflower’ and ‘flake’, have been synthesised by combining aqueous solutions of CaCl₂ and Na₂CO₃ under ambient reaction conditions. The unambiguous characterisation of these aragonite polymorphs is based on their characteristic powder X-ray diffraction patterns, Raman and FTIR spectra. The morphologies of these aragonite crystals have been confirmed by scanning electron microscopy. Both ‘cauliflower’ and ‘flake-like’ aragonites are spectroscopically similar to their needle-like congener, except that they are less crystalline in nature and they exhibit minor differences in their FTIR spectra. A plausible mechanism for the formation of these aragonites has been proposed based on the phase transformation behaviour during their syntheses.