And the Stone Is …
By Gary Roskin, G.G., FGA -- JCK Online, 2/1/2006 2:00:00 AM
November's gemological quiz elicited a number of responses. (See “Bright Gem, Big Question,” JCK, November 2005, p. 50.) The quiz was based on a situation that happened to Bob Wiener of Worldwide Diamond Co., Los Angeles, when he was presented with a ring set with a mystery stone, a blue pear shape surrounded by diamond accents. Equipped only with a loupe and his memory, he had to identify the stone, which showed rounded facet junctions, doubling, and little else.
Of the many good guesses from our readers, blue zircon was the most popular. The color was right, and zircon facet junctions can be rounded if polished incorrectly.
Other good guesses included kyanite, topaz, benitoite, synthetic forsterite, and apatite. Among the more unusual guesses were dyed quartz, synthetic blue quartz, taaffeite, and an aqua (beryl) and glass doublet.
The right answer, however, was there all along, and Rick Martin from Camarillo, Calif., figured out that it was greenish-blue zoisite. “If I was checking the stone, I'd also do a quick bare eyeball visual optics test to determine an approximate R.I.,” he wrote. “As a faceter, I can say that rounded facet edges can occur even on harder stones depending on the polishing method. Soft laps like Ultralaps often leave slightly rounded facet edges even on 7+ hardness gems.”
Its luster places it in a range of refractive index below sapphire. The greenish-blue color was curious. If you only remember tanzanite color for zoisite, then you would miss the identification. But this color is common for nonvarietal zoisite.
Special thanks to Bob Wiener of Worldwide Diamond Co.
