Microscopic Morphology of Porcelaneous Layers on Surface of Freshwater Cultured Pearls

The Scanning electron microscopy is used to study the morphological features of porcelaneous layers on surface of freshwater cultured pearls from Zhuji, Zhejiang Province, and the calcium carbonate polymorph of porcelaneous layers is identified by X-ray powder diffraction. It can be concluded that the porcelaneous layers are composed of vaterites with two kinds of microscopic morphology. The vaterites occur as elongated thin tablets with dimension of 4.4~7.1 μm×1.4~2.6 μm and length/width ratio of 2.3~3.7∶1, or as elongated fibers with dimension of 7.0~11.6 μm×0.9~1.5 μm and length/width ratio of 7.5~9.1∶1. These two kinds of microscopic morphology of vaterite crystals in porcelaneous layers of the pearls are clearly different from that of aragonites in nacreous layers.