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These 12 intensely colored copper-bearing tourmalines (0.31–1.04 ct) are reportedly from a new locality in Nigeria. Courtesy of Barker & Co.; photo by Robert Weldon.
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Copper-bearing (Paraíba-type) tourmaline is currently known from three countries: Brazil, Nigeria and Mozambique. Most of the Nigerian stones examined at GIA have been remarkably consistent in color (light blue to green) and trace-element composition (enriched in lead).
In October 2007, Bill Barker (Barker & Co., Scottsdale, Arizona) informed GIA about a new source of copper-bearing tourmaline in Nigeria that has produced material with colors similar to those of the original Paraíba tourmaline from Mina da Batalha, Paraíba State, Brazil. Barker's stones were notable for their wide range of saturated colors, which were quite different from those seen previously in Nigerian material. According to his supplier, the stones came from a new area for this tourmaline. The rough material consisted of broken fragments, so it was not possible to determine whether they were from a primary or secondary deposit. So far, he has obtained approximately 100 g of rough, from which 24 stones have been faceted in weights ranging from 0.2 to 4 carats.
Barker loaned 12 of the faceted stones (0.31 to 1.04 ct; figure 1) to GIA for examination. They showed highly saturated violet (five stones), green (one), blue (two), blue-green (two), and purple (two) colors that the contributors had not previously seen in Nigerian copper-bearing tourmaline. Only the two blue stones and one of the blue-green samples were reported to have been heat treated. The following properties were obtained on the 12 samples: RI—1.620 to 1.643; SG—3.01 to 3.12; and inert to both long- and short-wave UV radiation. Microscopic examination revealed typical "trichites," growth tubes and two-phase (liquid and gas) inclusions in nearly all samples.
EDXRF chemical analysis confirmed that the tourmalines contained significant concentrations of copper, and LA-ICP-MS indicated copper contents up to ~1.5 wt.%. Interestingly, most of these intensely colored tourmalines showed relatively low lead concentrations (<40 ppm). The new Nigerian stones bear a strong resemblance to their Brazilian counterparts in both color and chemistry.
Christopher M. Breeding, Kimberly Rockwell, and Brendan Laurs
