title: Chemical and mineralogical characterization of elbaites from the Alto Quixaba pegmatite, Seridó province, NE Brazil.
abstract: The Alto Quixaba pegmatite, Seridó region, northeastern Brazil, is a 60 degrees/80 degrees SW-trending subvertical dike discordantly intruded into biotite schists of the Upper Neoproterozoic Seridó Formation. It has three distinct mineralogical and textural zones, besides a replacement body that cuts the pegmatite at its central portion and in which occur, among other gem minerals, colored elbaites. Elbaites usually occur as prismatic crystals, elongate according to the c-axis, with rounded faces and striations parallel to this axis. Optically, crystals are uniaxial negative with strong pleochroism; refractive index extraordinary axis = 1.619-1.622 and ordinary axis = 1.639-1.643, birefringence between 0.019 and 0.021, average relative density of 3.07, and the following unit cell parameters: ao = 15.845 A, co = 7.085 A and V = 1540.476 A. There is alkali deficiency in the X site of 12-17%. The elbaites are relatively enriched in MnO (1.69 to 2.87%) and ZnO (up to 2.98%).
authors.affiliation: Centro Gemológico do Nordeste, Departamento de Mineração e Geologia, UFCG, 58109-170 Campina Grande, PB, Brazil. a.claudia1@ig.com.br
authors.forename: Ana C M
authors.initials: AC
authors.lastname: Ferreira
authors.forename: Valderez P
authors.initials: VP
authors.lastname: Ferreira
authors.forename: Dwight R
authors.initials: DR
authors.lastname: Soares
authors.forename: Hugo S
authors.initials: HS
authors.lastname: Vilarroel-Leo