Tim Ullmann’s research while affiliated with Johannes Gutenberg University Mainz and other places

Recently, several crystals of honey yellow danburite were found in an assemblage of ruby, sapphire, spinel, and tourmaline in the alluvial placer deposit Bai Cat at the route of the marble mountain An Phu in the Luc Yen area, Yen Bai province, Vietnam. Due to their rarity, bright color and excellent transparency, these specimens represent a fine gem-quality and were recognized for the first time at this location. The present study characterizes several specimens (rough and cut) by using standard gemological instruments, such as dichroscope, refractometer, hydrostatic balance, and an immersion microscope. The fluorescent response was investigated by using a UV lamp. The samples were further investigated by Raman-, photoluminescence-, FTIR-, and UV-Vis-NIR-spectroscopy. Additionally, electron microprobe and femtosecond-LA-ICP-MS were applied for chemical analysis. Fingerprints and two-phase inclusions (gas/liquid) were revealed by microscopic investigations and growth zoning was visible as an effect of different blue intensiThe spectroscopic characterization using Raman, UV-Vis-NIR, and photoluminescence confirmed the presence of rare earth elements (REE), while FTIR spectroscopy reveals the presence of hydroxyl in the danburite structure.

Gem-quality danburite was recently found in the summer of 2015 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, as well asand femtosecond LA-ICP-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 in average) together with the presence of other elements such as Al, Sr, Y, Hf, Pb, and Th, while the concentrations of some minor elements and transition metals were below detection limits. All Raman, UV-Vis-NIR, and photoluminescence revealed the bands related to rare earth elements. FTIR spectroscopy showed the presence of hydroxyl in the danburite structure.