Titanium-bearing synthetic alexandrite and chrysoberyl

The inclusions, compositions and spectra of synthetic reddish violet titanium-bearing chrysoberyl and synthetic alexandrites grown by the Czochralski method by Kyocera in Japan are described. These samples are compared with titanium-, chromium- and vanadium-bearing synthetic alexandrite cat's-eyes and six-rayed alexandrite stars. It is concluded that reddish violet chrysoberyl is coloured by trivalent titanium; the alexandrites are predominantly coloured by chromium with minor amounts of vanadium being also present. Both groups of samples contain inclusions typical of Czochralski-grown chrysoberyl. The colour and pleochroism of chatoyant and asteriated alexandrites is caused by a combination of some trivalent titanium and chromium with minor traces of vanadium. Three light bands are produced by three series of needle-like, titanium-bearing crystals, most probably rutile needles, which are orientated at about 60° to each other. The production technique of alexandrite cat's-eyes described in numerous patent documents is discussed.