Gemmological Characteristic of Pink Spinel from Yên Bái, Vietnam

Yên Bái in northern Vietnam is a new source of pink spinel, and there is a lack of research on spinel from this area.In this paper, the pink spinel samples from Yên Bái, Vietnam were systematically tested and studied by conventional gemmological instruments, laser denudation plasma mass spectrometer, ultraviolet-visible absorption spectrophotometer, fluorescence spectrometer and other testing instruments.The results showed that the spinel from Yên Bái have poor roundness, and some of the samples retained the original crystal shape, which are transparent to translucent, with strong fluorescence and etches on the surface.Rich solid inclusions and liquid inclusions can be seen under the microscope, such as octahedral inclusions, tubular inclusions, and a large number of liquid inclusions are distributed in healing fissures.The UV-Vis absorption spectra of the samples were basically the same and the magenta samples can be distinguished from other groups of samples due to its low V and high Fe characteristics.Most of the samples showed strong pink fluorescence with slightly different intensities, and the two-dimensional fluorescence spectra were approximately the same, showing characteristic lines of Cr³⁺. The results also showed that the main chemical compositions of the tested samples are MgO and Al₂O₃, the mass fraction of SiO₂ is between 0.70% - 1.06%, and the content of CaO is less than 0.1%, which is a typical chemical characteristic of dolomitic-marble type deposit spinel.Compared with marble type pink spinels from other areas, it is found that the marble type pink spinel from this area can be distinguished from the spinels from Tajikistan and Tanzania by using Fe/Sn, Ni, Zn and other elements, but there is a partial overlap with the spinel from Myanmar.