|
|
|
Figure 1. The rutilated quartz cabochons (12–20 mm) in this parcel proved to be doublets. Photo by M. Macrì.
|
Rutilated quartz has become more popular in recent years and now occupies a distinct niche in the gem market. This, combined with its limited availability – almost exclusively from Bahia, Brazil – has led to a significant increase in price. As with other gem materials, this price surge has encouraged imitation by enterprising entrepreneurs.
During a September 2005 trip to Teófilo Otoni, Minas Gerais, two researchers from the Laboratorio di Gemmologia Geo-Land in Rome were offered the seven-stone parcel shown in figure 1. The suspiciously low price and a preliminary inspection raised questions about the authenticity of the stones, prompting the two to perform a more detailed examination.
The refractive indices were 1.544–1.553, typical for quartz. However, when the stones were viewed from the side, it was evident that they were doublets, with a thin layer of semitransparent rutilated quartz glued to a thicker backing of transparent quartz that contained little or no rutile. The fact that the stones were assembled was even more obvious when the samples were immersed in water, as shown in figure 2.
|
|
Figure 2. When the center cabochon in figure 1 was viewed from the side in immersion, the fact that it had been assembled was readily apparent. This doublet consists of a rutilated quartz dome that has been backed with a piece of transparent quartz that contains relatively few rutile inclusions. Photo by M. Macrì.
|
Although a trained observer would easily detect this falsification in a loose stone, the same observer might fail to identify the doublets after they were mounted, since there were no gas bubbles or other evidence of the glue layer when they were viewed face-up with a loupe.
Michele Macrì and Simone Macrì
Laboratorio di Gemmologia Geo-Land, Rome
|
