Gemmological and Locality Characteristics of Tourmaline from Jiaoligetai, Inner Mongolia

A large pegmatite gem deposit containing tourmaline with significant development potential was found in the Jiaoligetai of Inner Mongolia. In this paper, the gemmological and mineralogical characteristics of the tourmaline were systematically studied by conventional gemmological tests, electron probe tests, laser ablation inductively coupled plasma mass spectroscopy, infrared spectra, ultraviolet-visible absorption spectra and Raman spectra. The characteristics of the tourmaline were summarized and compared with those of the other sources. The results showed that tourmaline samples from Jiaoligetai can be classified into two main varieties: blue and green. The fluorescence characteristics of the samples were inert under UV fluorescence, the refractive index ranges from 1.615 to 1.650, and the birefringence ranges from 0.015 to 0.020. The relative density is 3.050—3.158, and the value of dark one is higher. There are abundant inclusions of amorphous carbon, tiny tourmaline crystal, CO₂-bearing gas-liquid two-phase inclusions, and carbon filling in cracks. Based on chemical composition tests, the blue and green tourmaline samples from Jiaoligetai are elbaite, while the black ones are schorl. Both IR and Raman spectra show typical absorption of silicate and borate groups in tourmaline. UV-Visible absorption spectra show absorption bands at 414 nm and 720 nm, which cause the green and blue colour. Compared to other origins, the distinctive characteristics of Jiaoligetai tourmaline are higher Fe and Mn content, a certain linear correlation between w_FeO/w_Al2O3 and w_MnO/w_FeO, and the trace elements Zn, Sr, and Pb have higher concentrations.