Synthetic Alexandrite: Gemstone Information
Synthetic Alexandrite has been synthesized by a number of different processes, including Czochralski, floating-zone and flux. Inamori in Japan has also produced an alexandrite cat’s-eye. Pulled crystals sometimes advertized as alexandrite in rockhound-type journals are traps for the unwary amateur as they contain insufficient chromium to produce an alexandrite colour.
Identifying features of these synthetic chrysoberyls include undigested flux from crystals grown in precious metal crucibles, some gas bubbles, wavy fibres, weak yellow fluorescence from the crystal surface and supplemented by a red-orange response below the surface; this effect is seen under SWUV. The reader may consult O’Donoghue and Joyner (2003 passim) for further information.
Crystals grown in Russia may show flux-filled or partly filled negative crystals, some showing surface crazing and appearing white or pale yellow. Some crystals have shown ‘Venetian blind’ or shuttering effect. No natural chrysoberyl shows any such inclusions.
Alexandrite is well worth imitating and prospective purchasers should bear in mind that even the finest natural specimens do not show a very marked colour change; the green is dark and the ‘candle-light’ so often recommended for viewing alexandrite might make the stone as a whole hard to see at all. The flux-grown synthetics show too strong a colour change but the colours are fairly accurate. This cannot be said of the flame-fusion-grown vanadium-doped alexandrite simulant which looks far more like amethyst. Even today judicial proceedings feature this well-known (and quite attractive) product and there is always some expert witness to demonstrate how far gemmological education still has to go. Sometimes the specimen in question is not even forthcoming. A dark green Verneuil-grown spinel said to be made to imitate green tourmaline did show a dull red colour change and this could be passed off as alexandrite. Neither birefringence nor dichroism would be possible.
Composites with a dyed central gelatine filter have also been used as alexandrite simulants. While a number of natural yellow stones may be chatoyant enough to provide a reasonable cat’s-eye imitation, in no examples is the eye really sharp. In the ingenious ‘Cathay stone’ the eye is sharp though its host-glass is soft. Nonetheless this is an attractive and convincing product, at least through the shop window! Two types of glass are used, one in the form of hexagonal fibre-optic bundles. ‘Victoria cats-eye’, another glass product, is subject to devitrification and may on occasion show chatoyancy but it would be vague at the best. Transparent green and yellow chrysoberyl is neither imitated nor synthesized.