Natural Diamond with CVD-Like Fluorescence Pattern
Fluorescence images collected using the DiamondView are very useful in identifying whether a diamond is natural or laboratory grown (S. Eaton-Magaña and J.E. Shigley, “Observations on CVD-grown synthetic diamonds: A review,” Fall 2016 G&G, pp. 222–245). In many cases, type II natural diamonds show varying dislocation networks in these images. Meanwhile, high-pressure, high-temperature (HPHT) synthetic diamonds show cuboctahedral growth patterns, and chemical vapor deposition (CVD) laboratory-grown diamonds show growth striations.
The Mumbai laboratory recently received a 0.40 ct colorless round brilliant for diamond grading service. Spectroscopy identified it as a type IIa diamond, and it was examined further for color origin determination. DiamondView imaging showed uncommon and interesting patterns. In the figure above, the lower right is dominated by green fluorescence while the upper left shows mainly blue fluorescence, with a clear and straight boundary. Detailed examination revealed numerous sharp and clear dislocation lines in multiple orientations in both parts of this diamond. These dislocation lines were introduced by plastic deformation and provide strong evidence that the diamond crystallized in nature. It should be pointed out that the interface layer seen in the fluorescence image is uncommon for natural diamonds but similar to that of CVD laboratory-grown diamonds. Further photoluminescence spectroscopy analysis confirmed this natural diamond was treated by annealing under high pressure and high temperature to improve its color, reinforcing our assertion that advanced analytical study is often crucial in identifying a diamond.
Natural diamonds with fluorescence patterns similar to those of HPHT synthetic diamonds have also been reported previously (Spring 2013 Lab Notes, pp. 45–46). With recent advances in technology, manufactured diamonds with unique features have become more widely available on the market. Therefore, it is more important than ever to scrutinize each feature to ensure the appropriate identification results in such scenarios. Since natural and manufactured diamonds are structurally identical, we often need to rely on advanced gemological and spectroscopic data, particularly for such low-nitrogen diamonds, to correctly identify their origin.
