The following article is published courtesy of Gemological Instute of America’s Gems & Gemology’s eBrief
Author: Nathan Renfro
Image courtesy of: Gemological Institute of America
All Rights Reserved
Be-diffusion of corundum has become somewhat common in the gem trade, and has been applied to produce a wide range of colors. In fact, the Carlsbad laboratory routinely encounters blue, yellow, orange, pink, and red examples. Green is one of the more unusual colors for this material, especially in larger sizes, but we recently examined a 14.20 ct sample that was beryllium diffused.
The standard gemological properties were consistent with corundum. Microscopic examination revealed particulate clouds, flux-healed “fingerprints,” discoid-like fractures, and planar growth features. The desk-model spectroscope showed strong iron-related absorption centered at 450 nm. As expected, immersion displayed alternating blue and yellow color zones, a common feature in green sapphires.
The GIA Laboratory uses LA-ICP-MS to test all heat-treated corundum for the presence of beryllium. Since this stone showed features consistent with heat treatment, it was analyzed. We found it to contain an average Be concentration of just over 13 ppmw (27 ppma), enough to dramatically alter the color.
When beryllium diffusion was first detected in the early 2000s, the orangy pink to pinkish orange sapphires were recognizable by their surface-conformal color zoning. The vast majority of Be-diffused corundum now being processed, however, does not show this type of zoning because the stones are diffused all the way through. Microscopic evidence of high-temperature treatment can raise suspicion of Be diffusion, but only chemical analysis by a technique capable of detecting traces of Be can confirm the treatment.
GIA Laboratory, Carlsbad