Citation: | TAO Longfeng, JIN Cuiling, ZHANG Qianshen, HAN Xiuli. Mineralogy Characteristics and Coloration Mechanism of Green Tourmaline in Tanzania[J]. Rock and Mineral Analysis, 2022, 41(2): 324-331. doi: 10.15898/j.cnki.11-2131/td.202009280127 |
There are differences in the production characteristics, chemical composition, coloration mechanism and formation conditions of green tourmaline from different producing areas. At present, the mineral species and coloration mechanism of Tanzanian green tourmaline have not been solved, which makes it difficult for its scientific identification and quality rating.
To study the mineralogical characteristics and coloration mechanism of Tanzanian green tourmaline.
The mineral component was analyzed by infrared spectroscopy and Raman spectroscopy. Microtexture was characterized by polarized light microscopy. Electron probe microanalyzer, and ultraviolet-visible (UV-Vis) spectroscopy were applied to analyze the chemical composition.
The main mineral component of tourmaline in Tanzania was MgO tourmaline, which was characterized by single crystal, small grain, no cleavage, and split development, and can be used as a gemstone. The main chemical component of green tourmaline was SiO2, Al2O3, MgO and B2O3, with average contents of 37.52%, 36.26%, 9.65% and 8.42%, respectively. In addition, it contained a small amount of FeO, Cr2O3 and TiO2. Combined with the absorption spectrum in the ultraviolet region of 440nm, 600nm and 680nm in UV-Vis spectroscopy, it was concluded that the tiny amounts of Cr3+ replacing Al3+ into the crystal lattice was the main cause of the green color.
The mineralogical characteristics and coloration mechanism of green tourmaline in Tanzania was confirmed, which provides a theoretical basis for the scientific identification, further quality evaluation and utilization.
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Green tourmaline samples examined in this study (a—BX-1; b—BX-2; c—BX-3)
FTIR spectra of green tourmaline samples (a—compari-son of infrared spectroscopy of different green tourmaline samples; b—comparison of infrared spectroscopy of different parts of BX-2)
Raman spectrum of green tourmaline BX-1 sample
Polarized light microscopy images of green tourmaline samples (a—the crystal is light green; b—fracture; c—median bulge; d—gas-liquid inclusion; e—columnar inclusion; f—granular inclusion)
UV-Vis spectra of green tourmaline (a—BX-1; b—BX-2; c—BX-3)