Tourmaline Origin and Color Analysis Reports
A major item of controversy in the gem world is the definition of paraíba-type tourmaline. When this gem variety was first discovered in Brazil, the unusually intense "neon" or "electric" colors set it apart from any other tourmaline previously known. The color of this gem ranges from intense emerald green through "windex" blue-green to a rich sapphire blue and continuing along the spectrum to intense violet or even purple (similar to fine amethyst). Some have even reported red and pink stones. Apart from the intense colors, another remarkable feature of these gems is their relative lack of extinction.
The above photograph shows a portion (blue-green to blue) of the intense color range typical of paraíba-type tourmaline from Brazil. Photo: Wimon Manorotkul/Palagems.com |
Because the colors were so unusual, traders immediately began marketing the gems under the moniker "paraíba" tourmaline, after the Brazilian state where they were first found. Later, traders asked gemological labs to describe the gems on lab documents as "paraíba" tourmaline. This forced labs to come up with a definition for this variety.
One proposal was to determine the coloring agent(s) for these unusual varieties. Quickly it was determined that copper played a major role, along with manganese. But building a variety definition based on composition alone is fraught with danger.
First, our knowledge of what creates color is fluid, constantly changing as new discoveries are made. Once upon a time, chromium was considered the only cause of color in emerald. We now know that vanadium also plays a role, sometimes the dominant one. Similarly, until quite recently, iron was thought to be a major cause of color in yellow sapphire; today we understand that color centers are more important.
Second, the color of finished gems is dramatically affected by all manner of things unrelated to composition, such as variations in size, cutting, inclusions, orientation, pleochroism and color zoning. Thus composition alone is problematic.
Range of color observed in copper- and manganese-bearing tourmalines from Paraíba State, Brazil (Photo courtesy Robert Weldon). |
The LMHC has attempted to address these issues by building a definition that is both independent of origin and that incorporates color and composition (see LMHC Information Sheet #6). While the LMHC definition does not currently encompass stones in the violet-to-purple-to-red ranges, this could be a topic for future discussion. Currently, the AGTA GTC follows the LMHC definition.
Untreated purplish violet paraíba-type tourmaline from Mozambique. If heated, stones such as this often change to a rich blue-green color. |
Untreated electric green paraíba-type tourmaline from Mozambique. |
Does every tourmaline that contains a certain amount of copper/manganese qualify as a paraíba-type? In a word, no. The most important feature of a paraíba tourmaline is exactly that which made the gem famous in the first place – intensity of color. Thus if a gem submitted for testing lacks the necessary degree of color saturation, it will not meet the AGTA GTC's paraíba criteria, no matter what its chemistry. In such a case, color trumps chemistry.
A suite of tourmalines showing just a portion of the incredible color range of this gem. The blue-to-green gems in the center of the photo lack the necessary color saturation to qualify as paraíba-type. Photo: Wimon Manorotkul/Palagems.com |
Another issue is that of origin. While paraíba tourmalines were first found in Brazil's Paraíba State, stones of similar color and composition have now been found in the neighboring Rio Grande do Norte State (Brazil), Nigeria and Mozambique. Some purists have argued that the paraíba variety should be limited to Brazilian stones, but the decision of the LMHC was that this variety will be defined by color and composition, not country-of-origin. Upon request, member labs of the LMHC will identify the country-of-origin on their documents, thus satisfying all clients.
Heat-treated neon-green paraíba-type tourmaline from Mozambique. Photo: Wimon Manorotkul/Palagems.com |
Examples of AGTA GTC lab reports for paraíba and non-paraíba-type copper- and manganese-bearing tourmalines
As a special "by request only" service, the AGTA Gemological Testing Center uses the latest analytical techniques and its extensive gemstone database to support a professional opinion concerning the geographic origin of paraíba tourmaline and other copper- and manganese-bearing tourmalines. We issue three types of reports, as follows:
- paraíba-color tourmaline with origin
- paraíba-color tourmaline without origin
- copper- and manganese-bearing tourmaline that lack paraíba-type color intensity
Sample AGTA GTC Tourmaline Origin Report. Click on the report for a larger PDF image. |
Sample AGTA GTC Tourmaline Color Analysis Report. Click on the report for a larger PDF image. |
Sample report for copper- and manganese-bearing tourmaline that lacks the necessary saturation to qualify for a Color Analysis report. Click on the report for a larger image. |
References
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Abduriyim, A. & Kitawaki, H. (2005) Gem News International: Cu- and Mn-bearing tourmaline: More production from Mozambique. Gems & Gemology, Vol. 41, No. 4, Winter, pp. 360–361.
- Abduriyim, A., Kitawaki, H., Furuya, M. & Schwarz, D. (2006) Paraíba-type Copper-bearing Tourmaline from Brazil, Nigeria, and Mozambique: Chemical Fingerprinting by LA-ICP-MS. Gems & Gemology, Vol. 42, No. 1, Spring, pp. 4–21.
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Fritsch, E., Shigley, J.E., Rossman, G.R., Mercer, M.E., Muhlmeister, S.M. & Moon, M. (1990) Gem-quality cuprian-elbaite tourmalines from Sao Jose da Batalha, Paraíba, Brazil. Gems & Gemology, Vol. 26, No. 3, Fall, pp. 189–205.
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Smith, C.P., Bosshart, G. & Schwarz, D. (2001) Gem News International: Nigeria as a new source of copper-manganese-bearing tourmaline. Gems & Gemology, Vol. 37, No. 3, Fall, pp. 239–240.
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