Gemmological Characteristic of "Recrystallized" (Synthetic) Corundum in Market

"Reconstructed" and "recrystallized" gemstones have begun to appear in the jewelry market since the late 20^th century. Unlike synthetic gemstones made from chemosynthetic materials, the merchants claim that the raw materials of "recrystallized" gemstones are natural gem fragments or powder. In order to figure out the nature of "recrystallized" gemstones, 21 samples of "recrystallized" corundum sold by Anupam Gems Japan Ltd. are analyzed by conventional gemmological instruments, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-Vis) absorption spectroscopy, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The results show that these "recrystallized" corundum samples are actually flux-grown and flame-fusion synthetic gemstones. Synthetic gemstones made by chemosynthetic materials that marketed as "recrystallized" gemstones turn out to be a marketing ploy of merchants. "Recrystallized" corundum is monocrystal. The yellow sapphires all contain round bubbles. One of the samples is in uneven colour and has colourless or orange-red dendritic and mesh-like inclusions which range from translucent to opaque. And they contain few trace elements except for a small amount of chromophore Ni. However, natural yellow sapphires usually contain a large amount of Fe and other trace elements such as Mg, Ti, Ga and V. The blue sapphires are internally flawless without natural inclusions. The content of Fe and Ga elements is significantly lower than that of the natural blue sapphires, and that some samples contain the element Be. The rubies contain a large number of bubbles and curved growth striations, and some samples also contain uncrystallized molten materials. There is no Fe element detected and the content of trace elements is low. The colour-change corundum has a clean interior. In addition, the blue sapphires, rubies and colour-change corundum all have absorption peaks at around 3 309, 3 231 cm^-1 and 3 186 cm^-1 in infrared spectrum which are the characteristic peaks of flame-fusion synthetic corundum.