The Study Of Biomineral Characteristics Of Freshwater Cultured Pearls In Zhuji Of Zhejiang Province

With the angle of mineralogy and geomology comprehensive and systematic studies and freshwater pearls from China have been made by means of various modern testing methods. The results show that the main inner factors affecting the quality of pearl(colors, transparency, luster) are the arrangement way of mineral ,the grain size of mineral, the space distribution of mineral and the characteristics of mineral.By optical microscope, vaterite , a very unstable polymorphism of calcium carbonate, which rarely appears in nature, has been discovered. This paper describes the microscope characteristics of vaterite in lusterless freshwater pearls. The content of vaterite is one of the main inner factors which affects the quality of freshwater pearls.Raman spectrum is applied to freshwater cultured pearl of good quality with different colors. It's expected to find the relationship between colors, organic substance inside of pearl and Raman spectrum. The conclusions were as follows: the wavenumbers, 1134 and 1526cm^-1,only appeared in the Raman spectrum of red pearls, compared with the Raman spectrum of white pears; the Raman shifts which were found in Raman spectrum of violet pears, 1017, 1295, 2231 and 2609cm^-1, disappeared in the Raman spectrum of white and red pearls; the Raman shifts of certain organic compound, 1121, 1134cm^-1 of C—C wavenumbers and 1503, 1526cm^-1 of C = C wavenumbers , appeared in colored pearls and the organic substance was considered as polyacetylenic materials but not carotenoids which was proposed by previous researchers. Pearls with different colors obviously vary with Raman spectrum. More deeply the same color becomes, more stronger the Raman spectrum of organic substance is.Using AFM and traditional SEM , the authors studied the super-microscopic structure of pearls from micron- size to nanometer- size by observing the surfaces of pearls with different qualities , and discussed the correlation between the nanometer- size surface structure invisible with SEM and the physical properties (luster ,roughness and concomitant color) of pearl. The research shows that the grade of pearl has a positive correlation with ordering and compactness of layers , micro-layers , blocks and aggregates of aragonite.It is different between good pearls and poor pearls under Optical Microscope. Good quality pearls are mostly clean, no colors or very weak yellow. But poor quality pearls are dirty, snuff colors and have obvious circle texture. The prism layer in core of good pearl, appears under optical microscope and has parallel extinction under cross-section microscope. So it is considered to be aragonite.