GIA’s New York lab has spotted more large HPHT-treated
diamonds in recent weeks, according to the Gems & Gemology e-brief.
The largest was an 18.12-ct. diamond that received an F
color grade. The treatment was detected by observing a “tiny hexagonal graphite
inclusion surrounded by a tension fracture,” and confirmed by spectroscopic
The e-brief concludes that it is somewhat unusual to see such
large stones, since HPHT annealing can sometimes damage a diamond. But it is
not clear if this is a longer-term trend, and may simply be caused by better
starting material, the lab said.