Jewellery News Asia (August, 1999) writes:
A visually effective tanzanite imitation of Russian manufacture has entered the marketplace. This imitation is potentially confusing as it displays greenish blue to purplish pink directional pleochroism. Investigations by Shane McClure of GIA’s Gem Trade Lab in New York have revealed that this imitation is a synthetic forsterite (magnesium silicate)…..the magnesian end member of the forsterite-fayalite solid solution series of which the gemstone peridot is an intermediate member.
According to McClure the presence of scattered ‘pinpoints’ and small ‘needles’ suggest that this man-made material has been synthesized by the crystal pulling (Czochralski) technique. This imitation which is doped by cobalt, and therefore should display Co absorption spectrum and fluoresces red under LWUV and the Chelsea filter; specific gravity is 3.42 and refractive index is 1.635-1.670.
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