Turmalinas verdes e azuis, oriundas do Município de Banabuiú, CE.

Abstract

Tourmaline samples in the green and blue colors from the municipality of Banabuiú-CE were analyzed, and present gemological quality. The pegmatite source belongs to the Pegmatitic District of Solonópole-Banabuiú (DPSB), and is located in the center-west portion of the State of Ceará. A geological and mineralogical characterization of the tourmalines was carried out, focused in their intrinsic characteristics, such as causes of color (chromophores elements) and fluid components, through essentially spectroscopic analyzes. The methodology used in their characterization were measurement of relative density, Raman spectroscopy, molecular absorption spectroscopy in the infrared region by Fouríer transform (FTIR), molecular absorption spectroscopy in the ultraviolet-visible-near infrared region (UV-Vis-NIR). It was evidenced the presence of the hydroxyl group of type 0H3, which is located in the vertex of octahedral shares and coordinated by a cation Y and two cations Z. Data were provided for the determination of the chromophores, where the color causes of the tourmalines of Banabuiú are related to the absorptions promoted by Fe3+, Fe2+, Mn2+ and Mn3+ ions, in different concentrations, together with the effect contributions of the intervalence charge transfer (IVCT) and ligand-to- metal charge transfer (LMCT). Fe intensity is more pronounced in blue tourmaline samples than in green tourmaline samples, while Mn intensity is very poor in a blue tourmaline sample and absent in green tourmaline. The fundamental vibrations involve the hydroxyl groups, Si04 tetrahedra, AIOfí octahedra and triangular groups of B03.