Spectroscopy Characteristics of Emerald From Swat Valley, Pakistan
BAO Pei-jin1, CHEN Quan-li1, 2*, WU Yan-han1, LI Xuan1, ZHAO An-di1
1. Gemmological Institute，China University of Geosciences (Wuhan)，Wuhan 430074，China
2. Gemmological Institute, West Yunnan University of Applied Sciences, Dali 671000, China
Abstract：With the exhaustion of Colombian emerald mins, the emeralds from Swat vally, Pakistan have gradually dominated the market and the systematic research for emeralds from Swat valley, Pakistan is conducted by using conventional gemological instruments, infrared spectrum, Raman spectrum, UV-Vis-Nir spectrum and Laser Ablation （Microprobe） Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). The results show that the color of emerald from swat is dark green to dark bluish green, and the refractive index is 1.589～1.615. There are many kinds and quantities of inclusions in the emeralds from Swat, Pakistan. And the three-phase inclusions are rectangular with a clear boundary and obvious orientation, which is close to the three-phase inclusions in the emeralds from Russia, Zambia and Ethiopia. According to the UV-Vis-Nir spectroscopy and LA-ICP-MS analysis of the same sample with different colors, the UV-Vis-Nir spectroscopy show relatively strong R line absorption of 427, 608, 637 and 679 nm (O light) belonging to Cr in the dark region and absorption of 370 nm belonging to Fe in the o light, and the content of Cr and Fe in this region is relatively high. So emerald bands are caused by different amounts of Cr and Fe. The color of Emerald from Swat, Pakistan, is caused by Cr , and V contributes to color, and Cr/V is very high. According to LA-ICP-MS combined with the infrared spectrum, emerald from Swat , Pakistan belongs to alkali-rich emerald, and the fingerprint region of the infrared spectrum shows the same vibration absorption peak as common emerald. In the middle infrared region of 4 000～2 000 cm-1, low intensity 3 518 and 3 700 cm-1 belong to the asymmetric stretching vibration of type Ⅰwater and the other bands caused by water are saturated. The medium strong peak of 3 232 cm-1 is caused by polymer ion absorption of [Fe2(OH)4]2+. In the near infrared spectral region of 8 000～5 000 cm-1, the absorption band at 5 264 cm-1 belongs to the frequency combination absorption of ν3+ν2 of type Ⅰ/Ⅱ water in the direction perpendicular to the C-axis, and the peak of 7 097 cm-1 is caused by frequency double oscillation of type Ⅱ water. While weak ones of 7 187 and 6 842 cm-1 are caused by the frequency double oscillation of type Ⅰ water. In the parallel c-axis direction, the absorption band at 5 272 cm-1 belongs to the synthesis frequency absorption of ν3+ν2 of type Ⅰ/Ⅱ water, 7 073 cm-1 is the synthesis frequency vibration peak of type Ⅰ water, and the peak of 7 185 cm-1 belongs to the double frequency vibration of type Ⅱ water. In conclusion, the main chromaticity ions of emeralds in Swat Valley of Pakistan are Cr3+ and Fe3+, and the emeralds’ content of alkali metal ions is high and the emeralds from Swat Valley of Pakistan belong to type Ⅱ water-dominated emeralds.
Key words：Emerald; UV-Vis-Nir spectrum; IR spectrum; Causes of color
[1] Gubelin E J. Gems & Gemology, 1982，18(3): 123.
[2] Kazmi A H，Lawrence R D，Anwar J，et al. Economic Geology，1986，81：2022.
[3] Bowersox W Gary，Anwar Jawaid. Gems & Gemology, 1989，25: 16.
[4] Giuliani Gaston，Groat A Lee，Marshall Dan，et al. Minerals，2019，9(2): 105.
[5] Guo H S，Yu X Y，Zheng Y Y，et al. Gems & Gemology, 2020，56（3）：336.
[6] Zong K Q, Klemd R, Yuan Y, et al. Precambrian Research, 2017，290：32.
[7] Saeseaw S，Pardieu V，Sangsawong S. Gems & Gemology, 2014，50（2）：114.
[8] Pardieu V，Sangsawong S，Cornuz L，et al. The Journal of Gemmology，2020, 37（4）：416.
[9] Hu Y，Lu R. Gems ＆ Gemology，2019, 55（3）：338.
[10] Cui Di，Liao Zongting，Qi Lijian，et al. The Journal of Gemmology，2020, 37（4）：374.
[11] Zwaan J C，Seifert A V，Vrana S，et al. Gem ＆ Gemology，2005, 41（2）：116.
[12] Bosshart G. The Journal of Gemmology，1991，22（7）：409.
[13] Erkoyun H, Kadir S. Earth Sciences Research Journal，2016，20（3）：A1.
[14] QIAO Xin，ZHOU Zheng-yu，NONG Pei-zhen，et al(乔 鑫，周征宇，农佩瑧，等). Rock and Mineral Analysis(岩矿测试)，2019，38（2）：169.
[15] QI Li-jian，YE Song，XIANG Chang-jin，et al(亓利剑，叶 松，向长金，等). Geological Science and Technology Information(地质科技情报)，2001, 20（3）：659.
[16] Mashkovtsev R I，Thomas V G，Fursenko D A，et al. American Mineralogist，2016，101（1）：175.
[17] Groat L A，Giuliani G，Marshall D D，et al. Ore Geology Reviews，2008，34: 87.
[18] Wood D L，Nassau K. The American Mineralogist，1968，53: 777.
