The microstructures of nacreous layer and prismatic layer were studied by scanning electron microscopy ( SEM ) and atomic force microscopy ( AFM ) . The composition of nacreous layer and prismatic layer were analyzed by fourier-transform infrared spectroscopy (FTIR). The results show that the nacre layer of seawater pearl is composed of nacreous layer, prismatic layer and transition layer. The nacreous layer mainly contains aragonite, nanoscale aragonite microcrystal and organic grain interweave to form aragonite platelets. In the prismatic layer, there are two types of calcium carbonate, calcite and aragonite. The transition layer is composed of organic matter and a small amount of calcium carbonate. By studying the structure and composition of pearls, we conclude that its growth model are divided into three stages. Firstly, calcium ions from seawater are richly accumulated by pinctada, and the nucleation of calcium carbonate is gradully formed, induced by the secretion of organic matter. Calcium carbonate and organic matter grow together forming a prismatic layer. Secondly, with the crystal growth, organic matter secreted by pinctada changes forms a transition layer, which could regulate the growth of calcium carbonate. Thirdly, on the organic layer, nanocrystalline aragonite and organic matter interweave grow, forming aragonite plate. The aragonite platelets are stacked to form a dense and orderly layer of nacre.%利用扫描电子显微镜(SEM)、原子力显微镜(AFM),研究流沙湾海水珍珠珍珠质层和棱柱层的微尺度生长结构,采用傅里叶变换红外光谱仪(FTIR)对珍珠质层及棱柱层的成分组成进行分析.结果表明:构成海水珍珠珍珠层的珍珠质层,棱柱层和过渡层的微结构和组成是有所不同的,珍珠质层主要为文石型碳酸钙,纳米文石微晶颗粒与有机质颗粒交织形成文石板片,棱柱层中存在方解石和文石两种晶型的碳酸钙,过渡层是由有机质和少量的碳酸钙共同组成;通过对珍珠层结构和成分的研究,初步推断出其生长模式分三个阶段:(1)珠母贝从海水环境中富集钙离子,并分泌有机质诱导碳酸钙成核结晶,二者共同生长形成棱柱层;(2)棱柱层生长到一定阶段,晶体生长的同时珠母贝分泌的有机质发生变化形成一层有机质过渡层,调控碳酸钙的生长;(3)在有机质层上初始成核的纳米文石微晶颗粒与有机质颗粒交织堆砌生长,形成文石板片,文石板片层层堆叠形成结构致密排列有序的珍珠质层.
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