The Gemological Institute of America (GIA) has made an alarming discovery, namely, a natural white diamond covered by a thin (80 microns, or 0.003 inches) synthetic layer that colors it blue – and has warned that more such composites might be on the market. The 0.33-carat stone is a composite of CVD synthetic Type IIb diamond overgrowth on a natural Type Ia diamond. This is the not the first synthetic-natural hybrid diamond, as GIA notes that CVD diamond films have been applied to natural diamonds since the 1960s, and the successful addition of CVD-grown diamond layers on top of mined diamonds happened in 1993. But GIA says this synthetic overgrowth on a natural diamond with a Fancy color grade is the first it has ever seen.
Nitrogen is the most abundant defect in natural diamonds, and indeed was the substance forming the diamond substrate. Boron, on the other hand, is a rare impurity in natural diamonds that turns these exceptional stones blue. GIA writes it is "very unusual" to see both nitrogen and boron defects in a single diamond, but that is precisely what GIA found in this "boron-doped CVD synthetic".