Gemmological and Spectral Characteristics of Ruby from Huameuang, Houaphanh Province, Laos

Laos, a landlocked country, has a "T" type metallogenic belt rich in mineral resources, and its mining history of corundum can be traced back to the 1990s. However, there are only relevant studies on Huay Xai basalt sapphires in Laos at present, and there is no relevant literature on rubies in Laos at home and abroad. In this paper, the rubies from Laos were systematically studied using conventional gemmological test methods, Fourier transform infrared spectrometer, UV-Vis-NIR spectroscopy, LA-ICP-MS etc. The results showed that the colour of rubies from Laos are purple, irregular colour bands and blue zone can be seen in some samples.The internal cracks and cleavages are densely developed. The solid inclusions such as calcite, rutile, muscovite and two-phase fluid inclusions were detected by Raman spectrometer and the transparency is poor. The main chromogenic ions are Cr, Fe and Ti. It is a typical metamorphic deposit with high Cr and low Fe. In addition to the intrinsic absorption band of Al-O, the characteristic absorption peak of diaspore at 1 982, 2 122 cm^-1 and 2 924 cm^-1 also appeared in the infrared spectrum. There are 7 vibration peaks in Raman spectrum, which are mainly caused by bending vibrations and stretching vibrations of AlO₆. According to the mass fraction ratio relations of Mg, V, Ti, Fe and Ga, rubies from Laos can be preliminarily distinguished from other deposits.