Origin of color in cuprian elbaite from Sao José de Batalha, Paraibá, Brazil

George R. Rossman

Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125-2500, USA

Emmanuel Fritsch, James E. Shigley

GIA Research, Gemological Institute of America, 1660 Stewart Street
Santa Monica, California 90404-4088, U.S.A.

Abstract

Gem-quality elbaite from Paraibá (Brazil), containing up to 1.4 wt% Cu, is characterized using optical spectroscopy and crystal chemistry. The optical absorption spectra of Cu²⁺ in these tourmalines consist of two bands with maxima in the 695- to 940-nm region that are more intense in the E^c direction. The vivid yellowish green to blue-green colors of these elbaite samples arise primarily from Cu²⁺ and are modified to violet-blue and violet hues by increasing absorptions from Mn³⁺.

Data files: perpendicular to c; parallel to c

American Mineralogist, Volume 76, pages 1479-1484, 1991