Alexandrite substitutes on May 1 2009, at 14:48 in Alexandrite Synthetics and Imitations
Alexandrite is chrysoberyl BeAl2O4 with Cr3+ as an impurity, its colour depends on the type of illumination; in fluorescent light blue dominates, while red is predominant when viewed in light from a tungsten lamp. This is the so called "alexandrite effect". The most desirable colour change is rich blue–green to a deep raspberry red, and the shade of the colour can vary.
The impurity that produces the colour in alexandrite is Cr3+, but the ion sits in a different crystal environment and hence experiences a different ligand field. Synthetic alexandrite gemstones have been produced since 1973 and patented by Creative Crystals Inc of San Ramon, California.