Characteristic of Tourmaline from Jiaoligetai Area, Inner Mongolia

By using polarizing microscope, electron probe, ultraviolet-visible spectrometer, infrared spectroscopy and Raman spectroscopy, the gemmological characteristics of tourmaline from Jiaoligetai area, Inner Mongolia were studied. The conventional testing results show that the refractive index of the tourmaline from Inner Mongolia is between 1.615-1.650, the birefringence is between 0.015-0.020, and the relative density is 3.050-3.158. The refractive index, birefringence and relative density vary with the colour of samples. Under the polarizing microscope, it was found that tourmaline samples from Inner Mongolia contain a large number of fissure, liquid phase inclusion, gas liquid two-phase fluid inclusion and solid inclusion. The fluid inclusion mainly presents in irregular geometry and needle tube. Raman spectra show that the fluid inclusion is mainly water-containing and carbon-contaishow inclusions. Solid inclusion contains oxides of iron and magnesium. EPMA shows Fe content of samples ranges from 2.199% to 13.998%, which is higher than that from the other foreign origins, which can be used as an identification index of the origin. The UV-Vis spectra show that the main absorption areas are in the red and blue-purple regions, with similar main wavelengths. The narrow absorption band at 720 nm is related to Fe²⁺—Fe³⁺ charge transfer pairs, and absorption at 415 nm of some samples may be mainly caused by Mn²⁺ d electron transition. The infrared spectra of samples have typical tourmaline characteristics. The absobelong peak at 3 452-3 567 cm^-1 belongs to stretching vibration of O-H. absorption peaks at 1 397, 1 340, 1 391, 1 332, 1 273 cm^-1 belong to B-O, and absorption peaks at 1 093, 1 037, 798, 719 cm^-1 are related to Si-O-Si and O-Si-O. This paper comprehensively reports the gemmological characteristics of tourmaline from Jiaoligetai area, Inner Mongolia for the first time, which provides gemmological basic data for new tourmaline mineral resources and basic materials for the origin of tourmaline in the future study.