The Spectrum Characteristic Analysis of Mammoth Ivory
YIN Zuo-wei1, LUO Qin-feng2, ZHENG Chen1, BAO De-qing1, LI Xiao-lu3, LI Yu-ling4, CHEN Quan-li1*
1. Gemological Institute, China University of Geosciences, Wuhan 430074, China 2. Sichuan Provincial Gem & Precious Metal Testing Centre, Chengdu 610031, China 3. Gan Central-South Geological Resources Exploration Institute of Jiangxi, Nanchang 330029, China 4. Hebei Provincial Gem & Precious Metal Testing Centre, Shijiazhuang 050091, China
Abstract：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.
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