Identification of High-Luster and Lusterless Freshwater-Cultured Pearls by X-Ray Absorption Spectroscopy

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An aragonite phase was present in the prismatic layer of high-quality freshwater-cultured pearls, whereas a vaterite phase was present in low-quality pearls. The Ca K-edge XANES spectra of high-luster freshwater-cultured pearl samples indicate the aragonite phase at 4040 eV, with binding energy around 4045 eV, a shoulder on the trailing edge at 4054 eV, and hump peaks at 4061 and 4065 eV. The XANES spectra of lusterless or low-luster pearls show the broader absorption of combined aragonite and vaterite phases at 4050 eV, and a specific vaterite peak at 4058 eV.