猛犸牙的谱学特征分析

由于市场上出现猛犸牙饰品并且与现代大象象牙饰品极为相似，本文通过宝石常规测试、红外光谱、X粉晶衍射等研究手段，分析了猛犸牙的谱学特征并与象牙进行了比较。主要研究成果和创新点包括：两种牙在折射率和比重方面非常接近，猛犸牙折射率在1.52～1.53, 大象象牙折射率在1.54～1.55, 猛犸牙比重平均值为1.77, 大象象牙比重平均值为1.72; 采用Schreger 纹夹角来区分猛犸牙和大象象牙时要注意: 因为二者除了在各自牙体外层夹角不同外(本次猛犸牙样品“Schreger”纹理的夹角100°, 而大象象牙夹角115°), 在牙体中层和内层的夹角它们二者大小是相似的以至于无法区分, 另外通常亚洲象牙外层“Schreger”纹理的夹角小于120°，而非洲象牙则大于120°(这个区别可以用来鉴定亚洲和非洲象牙);通过红外光谱显示：与水分子有关的3 319，1 642，1 557 cm-1吸收峰在象牙中较明显，而猛犸牙中则较微弱;与胶原蛋白有关的吸收峰2 927和2 855 cm-1在象牙中表现得较为明显，而在猛犸牙中极其微弱，结果表明，经过长时间的埋藏，猛犸牙牙质中的胶原蛋白、结晶水已严重损失;X射线粉晶衍射结果表明猛犸牙的衍射峰比象牙的分裂更为明显、峰变尖锐，说明虽经几千年地下埋藏，猛犸牙中羟基磷灰石晶体结晶度有所提高。由此表明，猛犸牙经过埋藏后其有机物流失的同时无机物结晶程度提高，是鉴别两种牙类的重要参考。

The Spectrum Characteristic Analysis of Mammoth Ivory

Due to the similarities between mammoth ivory ornaments and modern elephant ivory ones in the market, the spectral properties of the two kinds of ivories were analyzed and compared in the present paper through the gemological tests, infrared spectrum and X-ray powder diffraction, etc. The research found that the refractive index and specific gravity of the two ivories are very similar. The refractive index of mammoth ivory is 1.52～1.53 whereas that of elephant ivory is 1.54～1.55.The specific gravity of mammoth ivory is 1.77 and that of elephant ivory is 1.72. It should be careful that Schreger angles are used to distinguish the two kinds of ivories, because the angles of inner and middle layers in the two kinds of tusks are similar except the angles of elephant tusk out-layers are larger than those of mammoth (The Schreger angle of the sample mammoth ivory belonging to out-layer tusks is 100°and that of elephant ivory is 115°). In addition, the out-layer Schreger angles of Asian elephants are normally less than 120°, while those of Africa elephants are bigger than 120°(This can be used to identify Asian and Africa elephant ivories). The infrared spectroscopy test shows that the water-molecule-related absorption peaks of 3 319, 1 642 and 1 557 cm-1 are more obvious in the modern elephant ivory samples than in the mammoth ivory samples; the collagen-related absorption peaks of 2 927and 2 855 cm-1 are obvious in the modern elephant ivory but extremely weak in the mammoth ivory. The results indicate that collagen and crystallized water in mammoth ivory reduced to a very low level after having been buried for a long period. X-ray powder diffraction results show that the diffraction peak splits of mammoth ivories are more obvious and sharp than that of elephant ivories, which means hydroxyapatites crystallized better despite being buried for thousands of years. Hence, it is an important reference for identifying the two kinds of ivories that the ivory organic matter was losing and inorganic matter crystallized better at same time after having been buried.