Peculiar Natural Type II Diamonds Showing Pseudo-Synthetic Features

Abstract

Identification of CVD-grown or HPHT-grown synthetic diamonds requires advanced laboratory techniques using such as photoluminescence spectroscopy or DiamondView™ in addition to the standard gemological tests. In this report we introduce examples of natural type II diamonds that show pseudo-synthetic features superficially resembling synthetic stones in such advanced analyses.
(1) All the colorless to nearly colorless CVD-grown synthetic diamonds of fifty-four samples in total that had been submitted to our laboratory since 2012 showed a Si-V peak at 737 nm (736.4/736.8 nm) in photoluminescence spectra. On the other hand, nine samples of natural type II diamond that had been analyzed around the same time showed the Si-V luminescence peak. This was accompanied by many other peaks including the one at 714 nm, and together with the existence of included minerals this indicates natural origin of the stones.
(2) Distinct sector zoning that shows greenish blue color luminesce and phosphorescence has been observed by DiamondView™ in two type II diamonds, which were submitted by different clients independently. This is generally a characteristic feature seen in HPHT synthetic diamonds, but cloud inclusions observed under magnification revealed that these samples were natural diamonds containing CO₂ that gives rise to characteristic peaks in FTIR analysis.