Caracterização gemológica das turmalinas de Quixeramobim

Abstract

Gemological characterization of minerals allows the evaluation of natural, synthetic, organic and artificial gems in relation to their gemological quality, including description of characteristics regarding their density, hardness, color and chemical composition. Tourmaline is a mineral that can be used as a gemstone and occurs in all colors. Deposits of this mineral group are found especially in pegmatites and alluvial deposits. This paper aims the gemological characterization of unstudied tourmaline specimens from Quixeramobim (CE) that have the potential to be used as gems. The samples selected for this study are derived from pegmatites from the Solonópole-Quixeramobim Pegmatite District, in the central portion of Ceará. For the characterization of tourmaline, refractometer, hydrostatic balance, dicroscope, spectroscope, ultraviolet lamp (UV) and gemological microscope were used, as well as energy dispersive spectroscopy (MEV-EDS) for analysis of the chemical composition of the studied samples. The specimens in blue, green and pink colors have similar gemological characteristics to tourmaline from other regions in the world; however, they may show variations in pleochroism, density and birefringence, which were attributed to the variation of the amount of FeO in the crystalline structure in some specimens. Minerals have a good degree of color and noticeable fluid inclusions. Through the use of the listed gemological instruments and accurate analysis, it was possible to perform an excellent characterization and compilation of mineral data from this region, besides proving that the specimens have good to medium characteristics to be used as gems.