Spectral Characteristics of Dark-Blue Corundum From Fangshan Mine, Shandong, China and Le-Shuza-Kone Mine, Mogok, Burma
ZHAO Qian-yi1, XU Chang1*, LIU Xian-yu2
1. Geological Institute of China University of Geosciences, Wuhan 430074, China
2. College of Jewelry, Shanghai Jianqiao University, Shanghai 201315, China
Abstract：To analyze spectral characteristics of dark-blue corundum from Fangshan mine, Changle, Shandong, China and Le-shuza-kone mine, Mogok, Burma comparatively, and to find out the valence state of iron and coloring mechanism of corundum from both of the mines, in this paper, we did research with the help of X-ray powder diffraction (XRD), microscopic laser RAMAN spectroscopy, microscopic Fourier infrared spectrum (FTIR), electron microprobe (EPMA), Mossbauer spectroscopy (CEMS) and other methods. The phase, spectral characteristics and composition of dark-blue corundum produced in Fangshan mine and Le-shuza-kone mine were studied. The X-ray diffraction results show that the corundum produced in the two mines is characterized by four diffraction peaks of 3.408 8/3.477 0 Å (012), 2.551 8/2.549 9 Å (104), 2.380 7/2.378 1 Å (110) and 2.085 0/2.089 4 Å (113) between 2θ angles of 25° and 45°. In addition, The corundum from Le-shuza-kone mine has a weak diffraction peak of 3.981 5 Å (110) between 2θ angles of 22° and 23°, and a weak diffraction peak of 2.314 9 Å (111) between 2θ angles of 38° and 40°, which are the characteristics of diaspore and boehmite, respectively. Raman spectral scattering peaks are mainly distributed in the two ranges of 350 to 450 and 550 to 850 cm-1. The 416 and 378 cm-1 are characteristic peaks of corundum. In the RAMAN results, the strong peaks of 415 and 377 cm-1 are displacements caused by internal structural deformation, and the Raman scattering peak at 749 cm-1 is attributed to Al—O stretching vibration. The 793, 811 cm-1 Raman peaks of corundum from Fangshan mine and the 707, 793, 1 239, 1 247 cm-1 Raman peaks of corundum from Le-shuza-kone mine can be used as the basis for distinguishing the origins. The infrared spectrum shows that the absorption peaks of 451, 603, 640, 779 and 1 088 cm-1 in the fingerprint region are common of the samples from the two mines, and in the functional group region, the absorption peaks of corundum of Le-shuza-kone mine has constitution water (—OH) peaks of 1 981, 2 110 and 3 311 cm-1, which can be distinguished from the characteristic peaks of corundum from Fangshan mine, Changle, Shandong, China. The dark-blue corundum from Le-shuza-kone mine, Mogok, Burma contains constitution water (—OH), which was involved in its formation, while the corundum from Fangshan mine, Changle, Shandong has no constitution water (—OH). According to the electron probe results and the electrovalence difference method, the iron element in the main crystal of corundum from Fangshan mine is Fe2+, and the Fe3+content of is zero. In the sample from Le-shuza-kone mine, Fe2+ accounts for 91.9% while Fe3+ accounts for 8.1% of the total amount of iron. Furthermore, the Mossbauer spectra were creatively applied in the research of Fe valence state in Fangshan-mine corundum, and the results show that the occurrence form of iron in corundum from Fangshan mine is Fe2+, and the dark-blue body color is caused by Fe2+, which is neither Fe2++Fe3+ nor Fe2++Ti4+ inter-valence charge transfer reported before.
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