The Gemological Institute of America (GIA) has spotted lab-grown stones and a simulant in a parcel of four blue gems submitted as natural sapphires for identification and origin reports.
The largest revealed polish lines on the surface, as well as gas bubbles and flow marks associated with blue coloration, when examined under a microscope, the GIA reported last week in the summer 2022 issue of Gems & Gemology. The 48.63-carat stone also contained weak snake patterns, which the GIA found using a polariscope. The observations led the GIA to believe it was a glass imitation, fashioned to resemble the real thing, the lab explained.
Meanwhile, for two of the sapphires, the irregularities were more difficult to discern, the GIA said. The 9.17- and 6.21-carat stones had surfaces coated in resin, which resembled matrix composed of materials commonly seen on natural rough corundum. Additionally, both contained brownish materials trapped inside cavities that looked similar to iron oxide stains, also normal for a rough sapphire. However, the resin melted with the touch of a hot pointer, and gas bubbles could be seen inside through a small, transparent area. After testing further, the GIA determined both were lab-grown sapphire.
The final piece of rough in the parcel, an 8.46-carat stone, had a frosted surface that made it difficult to see inside, but the GIA observed some natural-looking fingerprints and strong, straight inky-blue banding. The lab confirmed the stone was a natural sapphire from Madagascar that had been heat treated.
“This was an interesting study of how synthetics and simulants can be mixed with their natural counterparts to misrepresent a parcel,” the GIA explained. “However, careful examination and standard gemological testing are usually enough to identify them correctly.”
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