GIA presents paper on the irradiated gemstones issue

"...Most irradiated blue topaz sold in the United States in recent years has been imported from overseas, and most of it was irradiated at overseas facilities. The NRC says that there are presently no entities licensed to import and distribute irradiated blue topaz in the U.S. market. Yet, as of July 2007, irradiated topaz comprised an estimated 8% of the U.S. colored gemstone business at wholesale, making it one of America’s most popular gems..."

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Courtesy - jckonline.com