A new find of danburite in the luc yen mining area, Vietnam

In the summer of 2015, gem-quality danburite was found in an eluvial deposit of ruby, sapphire, spinel, and tourmaline at the foot of the marble mountains of An Phu in the Luc Yen area of Vietnam's Yen Bai Province. This danburite is notable for its honey yellow color and excellent transparency. For the present study, rough and cut samples were investigated by standard gemological methods, photoluminescence, spectroscopic analysis (Raman, FTIR, and UV-Vis-NIR), electron microprobe, and femtosecond LAICP-MS chemical analysis. Microscopic observations revealed fingerprints and two-phase inclusions (gas/liquid). Additionally, growth zoning was visible with different blue intensities under a long-wave UV lamp. The samples were characterized by high concentration of lanthanides (totaling about 1116 ppm on average) together with the presence of other elements such as Al, Sr, Y, Hf, Pb, and Th, while the concentrations of transition metals were below detection limits. All Raman, UV-Vis-NIR, and photo-luminescence results revealed the bands related to rare earth elements. FTIR spectroscopy showed the presence of hydroxyl in the danburite structure.