Study on Gemology Characteristics of the Turquoise from Mongolia
CHEN Quan-li1, WANG Hai-tao2*, LIU Xian-yu3, QIN Chen1, BAO De-qing1
1. Gemology Institute, China University of Geosciences, Wuhan 430074, China
2. College of Creative Design, Shenzhen Technology University, Shenzhen 518118, China
3. College of Jewelry, Shanghai Jianqiao University, Shanghai 201306, China
Abstract：Recently, one kind of turquoise with special appearance appears in the market. Their color is mostly pale blue and bluish green. Most of these materials are variegated with white or light blue-green plaques, whose boundaries are blurred. Some samples have similar flow structure on the surface, and their appearance is very similar to that of pressed turquoise. The raw material of the turquoise is mainly from Mongolia. The conventional gemological method, X-ray Fluorescence Spectrometer, Laser Raman Spectrometer and X-ray Power Diffraction were applied to the Mongolia turquoises in order to clarify their gemological properties, chemical and mineral composition in detail. The results show that the overall appearance of Mongolia turquoise is blue-green to deep blue-green with uneven distribution of color and uneven plaques on the surface. It often contains impurities such as quartz, pyrite, illite, feldspar and limonite etc. The refractive index of the turquoise in this area ranges from 1.60 to 1.62 (spot method), the relative density ranges from 2.43 to 2.76, and the relative density of the Mongolia turquoise is lower than that occurred in Hubei and Anhui. The samples fluoresce a weak ultraviolet to blue light glow under LWUV, with an inert reaction to SWUV. Weak ultraviolet light to blue fluorescence was observed in most samples under long-wavelength ultraviolet light, and fluorescence was inert under short-wavelength ultraviolet light. The main chemical composition of the Mongolia turquoise sample deviates from the theoretical chemical composition of turquoise, w (Al2O3) ranges from 26.75% to 30.30%, w (P2O5) ranges from 32.54% to 36.40%, w (CuO) ranges from 6.99% to 10.73%, w (FeO) ranges from 1.73% to 4.39%, w (ZnO) ranges from 0.35% to 2.93%. There is a certain amount of SiO2 in Mongolia turquoise samples, and the mass fraction can reach 2.38%~8.87%. This characteristic is different from that of other domestic turquoise areas, which contain nearly no or very trace SiO2. X-ray powder diffraction and infrared absorption spectra show that the main components of the uneven color plaques of Mongolia turquoise are turquoise, and they are natural and not optimised. Infrared absorption spectra show the vibrational spectra of crystal water, hydroxyl water and phosphate groups, which are consistent with those of natural turquoise. The laser Raman spectroscopy analysis of minerals with different transparency and color in Mongolia Turquoise show that the white opaque impurity minerals in the turquoise are sodium feldspar, white translucent impurity minerals are quartz, and brass with metallic lustre minerals are pyrite.
陈全莉，王海涛，刘衔宇，秦 晨，包德清. “外蒙料”绿松石的宝石学特征研究[J]. 光谱学与光谱分析, 2020, 40(07): 2164-2169.
CHEN Quan-li, WANG Hai-tao, LIU Xian-yu, QIN Chen, BAO De-qing. Study on Gemology Characteristics of the Turquoise from Mongolia. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2020, 40(07): 2164-2169.
