ZHANG Sheng-yuan, LIAO Bao-li*, DAI Zhi-gao, CHEN Yi-zhou, ZHANG You-yang

(College of Earth Sciences，Guilin University of Technology，Guilin 541006, China)

Abstract: In this study, we have collected seawater pearls, from a pearl farm in the Weizhou Island, Beihai City, Guangxi Zhuang Autonomous Region, with two months as a growth cycle and the growth times of 2, 4, 6, 8, 10 and 12 months, respectively, and have studied the structures and Micromorphologies of those Southern pearls of Hepu County. The results are given below. (1) Those Southern pearls with different growth cycles have different average monthly growth rates, with the fastest growth rates for cores of pearls grew in the first two months after nucleation, and then the stable growth rates of 30-35μm /month for rest parts of pearls grew lately. (2) The nacres of the Southern pearls with different growth cycles are composed of prismatic layers and aragonite platelets. The nacre of pearl with growth time of 10th months is product of alternating growth of prismatic layers and aragonite platelets of the transitional stage, whereas the Southern pearl with growth times of 12 months has multiple prismatic layers, with alternating growth phenomenon of the nacre and prismatic layer. (3) The sizes of the hexagonal aragonite platelets of the Southern pearls are decreased with the increase of the growth time, and the platelets are getting closer and closer together. The thicknesses of aragonite platelets of the Southern pearls with different growth cycles are related to various seasons. In summer, because the nacre was secreted quickly, the aragonite platelets are relatively thick. In winter, because the nacre was secreted slowly, the aragonite platelets are relatively thin. There are organic matter adhesive and nanoparticles between the layers of aragonite platelets. The Southern pearls with growth times of less than 8 months have simple shaped prismatic layers which were changed from the needle shaped prismatic one to the thick platelet shaped prismatic one. The prismatic layers of the Southern pearls with growth times of 10 and 12 months were changed from the acicular layer to the amorphous one. (4) The first prismatic layer of the Southern pearls with different growth cycles has the characteristiclaser Raman spectrometric peak of aragonite, while the second prismatic layer of the Southern pearls with growth time of 12 months have characteristic laser Raman spectrometric peaks of calcite and aragonite at the same time.

Keywords: The Southern pearls of Hepu County; Micromorphology; Prismatic layer; Scanning electron microscopy; Raman spectrometry

ACTA MINERALOGICA SINICA Vol. 43, No. 3, 2023, Page 371