gems, spinel, inclusions, Burma, Myanmar, Mogok

Spinel is a precious gem with a long history, but people are far less familiar with it. Previous studies on Mogok spinel from Myanmar focused on inclusion analysis, the chromogenic mechanism of single-color gemstones and heat treatment, whereas systematic studies on varicolored gem-grade spinel are lacking. In this study, gemological and geochemical analyses of four colors of spinel samples from Mogok were carried out, including basic gemology, inclusion morphology and identification, spectroscopy and geochemistry. The aim was to explore the occupation of elements in the spinel crystal structure, as well as the chromogenic mechanisms of varicolored spinels and the geological and geodynamic conditions of their formation. Mogok spinel samples are characterized by octahedral negative crystals filled with calcite and chondrodite inclusions, indicating that they are derived from a marble metamorphic-type deposit. The spinel samples of four colors are magnesia–alumina spinel (MgAl₂O₄). The contents of V and Cr in Mogok spinel are generally high, with a significantly high content of Zn being the most characteristic feature, while trace elements vary greatly. The infrared spectra of spinel samples of different colors are basically similar. According to the UV–Vis spectra, pink and red samples are mainly colored by Cr and/or V, whereas orange samples are mainly colored by V. Two broad absorption bands in the range 300–600 nm are mainly attributed to the spin-allowed and spin-forbidden transitions of Cr³⁺ and/or V³⁺. The purple samples are mainly colored by Fe, and the UV–Vis spectrum is mainly attributed to the spin-forbidden transition of TFe²⁺. This study is a useful supplement to research on Mogok spinels of various colors from multiple perspectives.