Emmanuel Fritsch, James E. Shigley, Meredith E. Mercer, Sam M. Muhlmeister, Mike Moon
Research Department
Gemological Institute of America, Santa Monica, California
George R. Rossman
Division of Geological and Planetary Sciences
California Institute of Technology, Pasadena, California,
Unusually vivid tourmalines from the state of Paraíba, 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 Cu2+ or a combination of Cu2+, Mn3+, and other causes. Some colors can be produced by heat treatment, but most also occur naturally.
Gems and Gemology 26, 189-205.