GIA finds natural diamond with synthetic coating


The Gemological Institute of America (GIA) has discovered a natural diamond that was covered with a synthetic coating that tinted it blue. The organization warns industry members that more of these stones could exist on the market.

Due to its cerulean hue, the 0.33-carat stone had been graded fancy blue. However, according to a lab report, the stone had a thin layer of lab-grown diamond on it, created using chemical vapor deposition (CVD).

Gemologists at the institute’s New York lab were tipped off to its synthetic coloring by a number of unusual characteristics. Firstly, the gem contained both nitrogen and boron defects, which is very rare. The stone also was a mixed type Ia and IIb diamond, which itself is highly uncommon. Through analysis from a DiamondView imaging machine, it was determined that the diamond itself had characteristics of a natural stone, but the top layer was manmade.

While this is the organization’s first such discovery, it warns that there are probably more stones like this out there.

“Identification of colored diamonds should be performed very carefully by looking for unusual characteristics, such as a straight boundary line associated with an interface plane, and fluorescence zones with sharp edges in DiamondView images,” says the GIA. “Examination of this fancy-colored composite diamond indicated that similar challenges could exist for colorless and near-colorless diamonds.”

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