In this paper, we present the main impurities in natural blue spinel from the Luc Yen mining area in Yen Bai province, Vietnam. Together with identifying impurities and their valence, we have taken into account the site of some impurities in the MgAl2O4 spinel structure by using sensitive techniques, including electron microprobe analysis (EMPA), UV-Vis-NIR, electron spin resonance (ESR), and X-ray absorption (XAS). | Vietnam Journal of Earth Sciences, 40(1), 47-55, Doi: Vietnam Academy of Science and Technology Vietnam Journal of Earth Sciences (VAST) Study of impurity in blue spinel from the Luc Yen mining area, Yen Bai province, Vietnam Le Thi Thu Huong*1,2, Tobias Haeger3, The-Long Phan4 1 Faculty of Geology, VNU University of Science, 334, Nguyen Trai, Hanoi 2 Institut of Earth science, Karl Franzens University, Universitaetsplatz 2, 8010-Graz, Austria 3 Institute of Geosciences, Johannes Gutenberg University, 55099- Mainz, Germany 4 Department of Physics, Hankuk University of Foreign Studies, Yongin 17035, South Korea Received 6 March 2017; Received in revised form 24 October 2017; Accepted 28 November 2017 ABSTRACT In this paper, we present the main impurities in natural blue spinel from the Luc Yen mining area in Yen Bai province, Vietnam. Together with identifying impurities and their valence, we have taken into account the site of some impurities in the MgAl2O4 spinel structure by using sensitive techniques, including electron microprobe analysis (EMPA), UV-Vis-NIR, electron spin resonance (ESR), and X-ray absorption (XAS). EMPA results indicated that blue spinel contains different impurities, including V, Mn, Ni, Zn, Ti, Cr, Fe, Co and Ca. UV-Vis-NIR, ESR and XAS studies revealed that the oxidation state of Mn, Co, Fe and Ni is 2+ while that of Cr is 3+. Particularly, Co2+, Fe2+, and Cr3+ ions are identified. They contribute to the color variation of the blue spinel samples. Our study also indicated Co2+ and Cr3+ located in the octahedral position of Al3+ of the MgAl2O4 structure. Keywords: Blue spinel; impurity; coloration. ©2018 Vietnam Academy of Science and Technology 1. Introduction1 The study about lattice defects and impurities in natural spinel has been carried out by some research groups to identify the origin of the color. For blue spinel, the coloring mechanism is very complex and .
