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Transparent bright blue Cu-bearing tourmalines from Paraiba, Brazil

Published online by Cambridge University Press:  05 July 2018

Ulrich Henn
Affiliation:
German foundation for gemstone research, 6580 idar-oberstein, West Germany
Hermann Bank
Affiliation:
German foundation for gemstone research, 6580 idar-oberstein, West Germany
Francisco Hermann Bank
Affiliation:
German foundation for gemstone research, 6580 idar-oberstein, West Germany
Hilmar Von Platen
Affiliation:
Institute for Geosciences, University of Mainz, 6500 Mainz, West Germany
Wolfgang Hofmeister
Affiliation:
Institute for Geosciences, University of Mainz, 6500 Mainz, West Germany

Abstract

Physical, crystal-chemical and absorption spectroscopical properties of blue tourmalines from a new occurrence in the State of Paraiba, Brazil, are described. Refractive indices, birefringence and specific gravity have been determined as ne = 1.615–1.620, no = 1.632–1.640, Δn=−0.017 to −0.020 and 3.04–3.07g/cm3. Microprobe analyses proved the samples to be elbaites, which are relatively Mn-rich and contain 2.1 wt. % CuO and 0.5 wt. % Bi2O3. Lattice constants are ao = 15.854(4) and co = 7.102(1) Å. The blue colour is due to pleochroic absorption bands of Cu2+ and Mn3+ with maxima at 700 and 520 nm respectively.

Type
Mineralogy and Petrology
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1990

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