gems, spinel, Vietnam, Luc Yen

Yên Bái in northern Vietnam is a new source of pink spinel, yet research on spinels from this locality remains limited. In this study, pink spinel samples from Yên Bái were systematically examined using conventional gemmological instruments, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), ultraviolet-visible absorption spectrophotometry, fluorescence spectrometry, and other analytical techniques. The results showed that the spinels from Yên Bái exhibit poor roundness, and some retain their original crystal habit. The samples range from transparent to translucent, with strong fluorescence and surface etching. Rich solid and liquid inclusions were observed under the microscope, including octahedral inclusions, tubular inclusions, and numerous fluid inclusions distributed along healing fissures. The UV-Vis absorption spectra were generally consistent across samples; however, magenta-colored stones could be distinguished from others by their low vanadium and high iron content. Most samples exhibited strong pink fluorescence, with slight variations in intensity. Two-dimensional fluorescence spectra were largely consistent and showed characteristic Cr³⁺ emission lines. Chemically, the main constituents were MgO and Al₂O₃, with SiO₂ ranging from 0.70% to 1.06% and CaO content below 0.1%—a typical signature of spinel from dolomitic-marble-type deposits. Compared to marble-hosted pink spinels from other regions, the Yên Bái material can be distinguished from spinels from Tajikistan and Tanzania based on trace elements such as Fe/Sn, Ni, and Zn, though partial overlap exists with spinels from Myanmar.