| Pinctada fucata martensii Dunker is not only the main species that was used in production of marine free pearl but also the pearl oyster that can produce non-nucleus pearl. In order to discover the compositions mineral phases and structural characters of three kinds of non-nucleus pearl produced by P. fucata martensii, several techniques, including thermogravimetric analysis, fourier transform infrared spectrometry, X-ray diffraction, optical microscope and scanning electron microscope (SEM), were used here in study on millet pearl, tablet pearl and variegated tablet pearl. These results will provide some theoretical help for production of millet pearl and tablet pearl.1. Thermogravimetric analysis showed that all the three kinds of non-nucleus pearls were mainly composed of calcium carbonate and organic polymer material such as proteins and polysaccharides. The ratio of CaCO3was95.32%,95.57%and89.84%for millet pearl, tablet pearl and variegated tablet pearl respectively.2. Fourier transform infrared spectroscopy analysis indicated that the infrared spectrum characteristic peaks were similar each other for the three kinds of non-nucleus pearls. Although aragonite was the main mineral compositions for these pearls, there were two special absorption peaks that had never found in standard aragonites. The two special peaks suggested that non-nucleus pearls was consisted of not only aragonite but also a small amount of organic matter and water, agreeing with the result of thermogravimetric analysis.3. X-ray diffraction analysis revealed that both of millet pearl and tablet pearl were made up of aragonite, whereas variegated tablet pearl consisted most of aragonite and a small amount of calcite crystallites. Although the diffraction peak position of either kind of pearls was the same as the standard aragonite, the peak values were quite different. These results were similar to that derived by fourier transform infrared spectroscopy but there was some differences for the variegated tablet pearl.4. Surface analysis with SEM showed the surface crystal layer of the millet pearl was fused perfectly without free single aragonite crystal, holes and spots, presenting smooth appearance. For the tablet pearl, the fusion of surface crystal layer was worse than that of the millet pearl. Although the fusion area was also smooth, there were many single aragonite crystal in the surface crystal layer of tablet pearl. As for the variegated tablet pearls, the fusion of surface crystal layer were worst among the three kinds of pearls. Single aragonite crystal was not found in the surface crystal layer of tablet pearl. However, there was a lot gap in the surface resulting in bumpy appearance for the tablet pearl. 5. Inner structures analysis with optical microscope and SEM revealed that there had no amorphous matrix in the central region of millet pearl, whereas there were a little of amorphous matrix with some inorganics in the central region of tablet pearl and a lot of amorphous matrix with single aragonites and other inorganics in the central region of the variegated tablet pearls respectively. Although regular aragonite tablet was the main component for either of the three kinds of pearls, there was some difference for prismatic layer. No prismatic layer was observed in millet pearl. However, a few of prismatic layers were observed near the crack in tablet pearl, and a lot of prismatic layers were found in inner of variegated tablet pearls. The thickness of sole aragonite tablet was different between the surface layers and inner layers (0.3-0.6mm from surface). For the millet pearl, it was0.24±0.03um in surface layers and0.28±0.03um in inner layers. As for tablet pearl, the thickness of aragonite tablet was0.25±0.03um and0.39±0.03um in surface layers and inner layers respectively. Moreover, the thickness of aragonite tablet was0.31±0.03um in surface layers and it was0.43±0.04um in inner layers. |
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