Gem News International Gems & Gemology, Spring 2018, Vol. 54, No. 1

Opal from West Java, Indonesia

Indonesian opal cabochons, 6.94 and 3.79 ct.
Figure 1. These cabochons, weighing 6.94 ct and 3.79 ct, were among the Indonesian opals at Rare Earth’s AGTA booth. Photo by Robison McMurtry.

At the AGTA show, Rare Earth Mining Co. (Trumbull, Connecticut) displayed an unexpected material: Indonesian opal reportedly from West Java. Two cabochons (figure 1) yielded a refractive index of 1.45 and a specific gravity of 2.13, consistent with opal. Energy-dispersive X-ray fluorescence (EDXRF) analysis revealed the presence of copper.

According to Rare Earth’s Curt Heher, the material was first seen in the spring of 2017. While the opal comes in a wide range of colors, including browns and blues, the greenish blues were of particular interest. Rare Earth displayed cabochons where this was the primary hue, with the accessory colors distributed in an aesthetically pleasing manner.

Jennifer-Lynn Archuleta is editor of Gems & Gemology. Nathan Renfro is the manager of the gem identification department and microscopist in the inclusion research department at GIA in Carlsbad, California.