- Joined
- Oct 21, 2004
- Messages
- 5,096
From GIA Insider..., January 28, Volume 11, Issue 2
"Jan. 28, 2009
Lab Alert:
GIA Reports Pink Color Around Growth Tubes in Copper-Bearing Tourmalines Results from Natural Irradiation
Samples of blue to blue-green, copper-bearing tourmaline containing surface-reaching growth tubes surrounded by intense pink "sleeves" have recently been seen in the trade. In response to rumors of possible diffusion treatment, GIA Laboratory staff members John I. Koivula, Kevin Nagle, Andy Shen and Philip Owens carefully examined several of these tourmalines over the past year. Based on this examination, the GIA team determined that the pink zones were produced by fluids containing naturally occurring radioactive material.
In all instances where pink coloration was observed, the growth features surrounded by the pink color reached the surface of the stones. In cases where growth tubes did not reach the surface, no pink color was seen. When these pink zones were viewed down their length, the color was observed to bleed out into the surrounding tourmaline host, becoming weaker until it gradually faded away. If post-growth matter in the tube created a blockage, coloration occurred only to that point. Additionally, any cracks extending from or between the growth tubes also showed a pink color.
Radiation is known to produce pink-to-red color in tourmaline. The coloration of surface-reaching features in tourmaline by invading radioactive fluids has not been reported in the literature; however, there have been reports of both smoky quartz and green diamonds with coloration that was caused by exposure to naturally occurring radioactive fluids. This mechanism explains all the observations of pink and red in these tourmalines.
"Since radiation is the cause of pink color in tourmaline, the presence of these features should not be attributed to any type of intentional diffusion, but rather to the influx of radioactive fluids in their post-growth environment," said GIA Laboratory Chief Gemologist John I. Koivula, one of the study''s authors.
All the copper-bearing tourmaline samples with this feature observed thus far have come from Mozambique. This suggests that this type of inclusion feature may be characteristic of that locality.
The presence of the pink zones in these otherwise blue to blue-green gems also provides proof that the host tourmalines were not heat treated, since the temperature needed to treat copper-bearing Mozambique material exceeds the published stable temperature for pink-to-red color in tourmaline.
An article by Koivula and his colleagues detailing these observations will appear in the Spring 2009 issue of GIA''s Gems & Gemology, due out in April. Subscribe online or call toll-free (800) 421-7250, ext. 7142. Outside the U.S. and Canada, call (760) 603-4000, ext. 7142."