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Gem-Quality Cuprian-Elbaite Tourmalines From São José Da Batalha, Paraíba, Brazil

1990; Gemological Institute of America; Volume: 26; Issue: 3 Linguagem: Inglês

10.5741/gems.26.3.189

2376-4473

Emmanuel Fritsch, James E. Shigley, George R. Rossman, Meredith E. Mercer, Sam Muhlmeister, Mike Moon,

Lichen and fungal ecology

Unusually vivid tourmalines from the state of Paraiba, in northeastern Brazil, have attracted great interest since they first appeared on the international gem market in 1989. This article describes what is known of the locality at this time, but focuses on the most striking characteristic of these gem tourmalines: the unusual colors in which they occur. Quantitative chemical analyses revealed that these elbaite tourmalines contain surprisingly high concentrations of copper, up to 1.92 wt.% Cu (or 2.38 wt.% CuO). Their colors are due to Cu^(2+) or a combination of Cu^(2+), Mn^(3+), and other causes. Some colors can be produced by heat treatment, but most also occur naturally.