Abstract The quality of natural and cultured pearls depends on the size, shape and properties of the surface. The inner structure of the pearl is not known, and not taken into account. Indeed, it is assumed that the cultured pearl is a nucleus covered by a thin organic layer, a thin prismatic layer and a thick nacreous layer. The examination of spherical and pear shape samples resulting from the grafting of the black lip pearl oyster (Pinctada margaritifera) shows that this assumption is, in most cases, erroneous. Optical, electron and atomic force microscopic observations, infrared and Raman analyses, as well as micro X-ray fluorescence and micro X-ray absorption near-edge spectroscopy data show that the inner structure of a pearl does not depend on its shape. Both circle or pear shape and spherical pearls show a large variability of the inner structures and composition. There are no two identical samples. Moreover, the arrangement is irregular within a single pearl, and some structures (aragonitic pseudo-prisms) do not exist in the shell.

中文翻译：

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里面的黑珍珠

摘要 天然和养殖珍珠的质量取决于表面的大小、形状和特性。珍珠的内部结构未知，也未考虑在内。事实上，有人认为养殖珍珠是由薄有机层、薄棱形层和厚珍珠层覆盖的核。对黑唇珍珠贝 (Pinctada margaritifera) 嫁接产生的球形和梨形样品的检查表明，这种假设在大多数情况下是错误的。光学、电子和原子力显微观察、红外和拉曼分析，以及显微 X 射线荧光和显微 X 射线吸收近边光谱数据表明，珍珠的内部结构并不取决于其形状。圆形或梨形珍珠和球形珍珠的内部结构和成分都显示出很大的可变性。没有两个相同的样本。而且，单颗珍珠内的排列是不规则的，在贝壳中不存在一些结构（文石假棱柱）。