(1. School of Earth Science and Geological Engineering, Sun Yat-sen University, Guangzhou 510275, China;
2. Guangdong Provincial Key Laboratory of Mineral Resources & Geological Processes, Guangzhou 510275, China;
3. Guangdong Museum, Guangzhou 510623, China)

Abstract: The unique charm of pearl attributes to its unique luster, whose strength is directly affected by the microstructure of nacre, determining the pearl’s quality. In this study, we selected seawater cultured pearls with different luster produced in a stream haven of Leizhou Peninsula, China. By using field emission scanning electron microscope (FE-SEM), the microstructure in different parts of the samples was systematically observed and compared. In addition, combined with X-ray diffraction (XRD) analysis, the crystal orientation of aragonite crystals in nacre and their impact on the pearl luster were understood. Results reveal that luster’s strength is closely related to surface finish, defects, preferred orientation degree of aragonite crystals and the content of organic matter. The better aragonites in nacre crystallize are and the higher the degree of preferred orientation is, the better the pearl luster will be; the presence of organic matrix in the outer surface of pearl improves pearl’s roundness, rendering pearls with an enhanced luster; pores in pearl surface absorb the incident light, reducing the total amount of light on nacre surface, whose impact on the nacre structure and its causes need further study.

Keywords: seawater cultured pearl; luster; microstructure; FE-SEM; XRD analysis

Email: liqian0329@163.com

ACTA MINERALOGICA SINICA Vol. 36, No. 2, 2016, Page 225-230