Characterization of vaterite in low quality freshwater-cultured pearls

Vaterite is a very unstable phase of calcium carbonate rarely occurring in nature. We report a discovery of vaterite in the low quality freshwater-cultured pearls of the shell Hyriopsis cumingii (Lea). Experimental evidences are given by optical microscope, micro-infrared spectroscope and X-ray diffraction pattern. The formation mechanism of vaterite in these special pearls is discussed.