Transparent Bright Blue Cu-Bearing Tourmalines from Paraiba, Brazil

Ulrich Henn, Hermann Bank, Francisco Hermann Bank, Hilmar von Platen and Wolfgang Hofmeister
German foundation for gemstone research, 6580 idar-oberstein, West Germany
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.

Keywords: copper • tourmaline • optical properties • chemical composition • crystal chemistry • absorption spectrum • Brazil

Mineralogical Magazine; December 1990 v. 54; no. 377; p. 553-557; DOI: 10.1180/minmag.1990.054.377.04
© 1990, The Mineralogical Society
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