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Year 6 Issue 12 January 2008
New Paraiba Tourmaline
 
 
 
 
         
  New Paraiba Tourmaline  
 

     Copper-bearing (Paraiba-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., Scotts-dale, Arizona) informed GIAabouta new source of copper-bearing tourmaline in Nigeria that has produced material with colors similarto those of the original Paraiba tourmaline from Mina da Batalha, Paraiba State, Brazil. Barker's stones were notable fortheirwide 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.


 
   
     These 12 intensely colored copper-bearing tourmalines (0.31 -1.04 ct)are reportedly from a new locality in Nigeria.

     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 contribu¬tors 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 12samples: Rl—1.620 to 1.643; SG—3.01 to 3.12; and inert to bothlong-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 thatthetour-malines contained significant concentrations of copper, and LA-ICP-MS indicated copper contents up to ~1.5wt.%. Interestingly, most of these intensely colored tourmalines showed relatively low lead concentrations (<40 ppm).Ttie new Nigerian stones bear a strong resemblance to their Brazilian counterparts in both color and chemistry.