BACKGROUNDThere 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.
OBJECTIVESTo study the mineralogical characteristics and coloration mechanism of Tanzanian green tourmaline.
METHODSThe 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.
RESULTSThe 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.
CONCLUSIONSThe 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.