|Chemical composition||Silicon dioxide SiO2|
|Optic nature||Uniaxial +|
|Refractive index||1.544 - 1.553|
|Specific gravity||2.63 - 2.65|
Ametrine is a variety of quartz that contains both amethyst and citrine sectors in the same crystal.
Ametrine is only found in one mine in the world. The Anahi Mine in Bolivia is the major world producer of ametrine. The mine first became famous in the 17th century. A Spanish conquistador received it as a dowry when he married a princess from the Ayoreos tribe named Anahi. Ametrine was introduced to Europe through the conquistador's gifts to the Spanish queen.
In the gemology world, ametrine was originally described as a curious find in 1980. (Hehar, Koivula, Vargas, 1980). Its locality was originally given as Rio Grande do Sul in Brazil, but later determined to be in Bolivia. The material met with immediate suspicion, as Kurt Nassau had a synthetic example of amethyst/citrine in his collection for several years prior to the "find" in 1980.
Several unsuccessful tests were conducted in order to see if this bi-colored quartz was actually the result of a series of treatments. Then, it was discovered that specimens of a specific sectored amethyst from Minas Gerais, which exhibited alternating sections of dark and light amethyst, could indeed be altered to ametrine. This was done with a succession of heat treatments followed by irradiation coupled with subsequent annealing. (Gems & Gemology, Spring 1981).
The results of this experimentation made "naturally occurring ametrine" suspect and controversial at best. Ametrine, in the '80s, was presumed to be 100% the result of treatment.
That all changed when the Anahi Mine in Bolivia was shown to produce vast quantities of naturally occurring ametrine, (insert egg on face), in the early 90's. Between 1989-1994, 100 tons of naturally occurring ametrine xls were extracted from the Anahi Mine. (G&G, Spring 94).
This is a valuable lesson for gemologists.
We must be careful when extrapolating experimental evidence.
Just because something CAN be done, does not mean it IS being done.
As mentioned earlier, there were examples of bi-colored, synthetic, amethyst/citrine in existence in the '70s, but it was not until 1994 that Russian synthetic ametrine was available for commercial distribution. These crystals were being produced by hydrothermal growth from alkaline solutions. We are able to separate the synthetic material from natural on the basis of growth features (twinning and color zoning), sophisticated EDXRF chemical analysis and IR spectral analysis. (G&G Summer 1999)