Identification Characteristic of Large Near-Colourless HPHT Synthetic Diamond from China

Since the beginning of 2015, a large amount of melee-sized near-colourless HPHT synthetic diamonds have emerged as side stones on the jewelry pieces, which is a big challenge for the routine identification in gem laboratory.Recently, large near-colourless HPHT synthetic diamonds have also been appeared.For studying the characteristics of near-colourless HPHT synthetic diamonds grown by different producers, the authors collected 20 pieces of near-colourless HPHT synthetic diamond samples weighing from 0.06 to 0.67 ct, from a diamond producer located in Shandong Province, China and conducted a series of gemmological and spectroscopic tests on them.For 10 pieces of round brilliant cut diamond samples, the colour is D to E, and clarity is up to VS, showing attraction to magnet due to the metallic inclusions, and anomalous birefringence with weak low-order interference colours under crossed polarizer.The other 10 pieces of samples are rough with combination form of cubic and octahedral faces, and the small faces of (110) and (113) can be partly seen.They can also be attracted by magnet because of metallic inclusions.UV-Vis spectrum showd weak band at 270 nm, and infrared spectrum indicated all samples were type Ⅱa with variable minute amounts of element B.No characteristic peaks were detected in PL spectrum, except the strong bluish green phosphorescence, as well as the clear zoning characteristics of cube-octahedral growth sector observed under DiamondView^TM.The identification of these HPHT synthetic diamonds can be easily done with features revealed by FTIR, UV-Vis, microscopic observations, as well as luminescence imaging techniques.