Gemmological and Spectral Characteristics of Pink Garnet from Mogok, Myanmar

In this paper, 2 pink garnet samples from Mogok, Myanmar were studied by electron microprobe, laser ablation inductively coupled plasma mass spectrometer(LA-ICP-MS), Raman spectrometer, infrared spectrometer and ultraviolet-visible spectrometer and other conventional gemmological tests. Infrared and Raman spectra results indicated that they are close to the grossular endmember. The chemical composition of the samples was tested by electron microprobe. The result also demonstrated that the 2 samples are close to the endmember of grossular. The average chemical structure formulas of the samples G1 and G2 are Ca_3.08(Al_1.84Ti_0.06Fe_0.01Mg_0.01)_1.92(Si_2.90Al_0.10)_3.00O₁₂and Ca_3.06(Al_1.84Ti_0.08Fe_0.01Mg_0.01)_1.94(Si_2.91Al_0.09)_3.00O₁₂, respectively. The test result of LA-ICP-MS showed that both samples contain trace elements such as Ti, Fe, Zr, Mn, Nb, Ga and Sn. The content of Ti in the samples, ranging from 5 444 to 10 035 ppm, is higher than that in raspberry-red grossular from Mexico, while the content of Mn is lower, only 47 to 132 ppm. Ultraviolet-visible spectra analysis revealed that the samples G1 and G2 have absorption bands at 489 nm and 495 nm, respectively. There is an absorption broad band centered at 550 nm in both samples. Combined with the trace elements in the samples and the previous research about the role of Mn in garnet and other silicates, it is believed that the absorption broad bands are related to Mn³⁺, which means their colour is probably due to the presence of small amounts of Mn³⁺.