The Gemological Institute of America (GIA) gemological laboratory has reported a recent increase in the number of HPHT (high pressure-high temperature)-treated diamonds submitted for grading.

Very few of the HPHT-treated diamonds were reported as such, the GIA said, which is a violation of the GIA rules that stipulate that gemstone treatments on a given stone must be reported when it is sent to the lab.

The diamonds identified as treated range from 3 carats to nearly 20 carats in size, and from D to J color, although most are G color or better.

Senior Vice President of the GIA Laboratory and Research Tom Moses said that the range of diamonds "subjected" to the HPHT treatment had expanded. However, Moses said that the GIA was confident that the GIA's research into the diamond treatment had given it the tools necessary to identify treated stones. Moses said the GIA didn't know whether the rise in HPHT-treated diamonds was due to a new source or "an attempt by some clients to test the systems at GIA."

Moses stressed that the GIA's mission was to "protect the public trust in gems and jewelry" and that the institute took that role very seriously.