Answer:True synthetic alexandrite itself is rarely seen because it is much easier to create synthetic corundum and synthetic spinel with color change properties that look like alexandrite. Synthetic corundum changes from a purple resembling amethyst under artificial light to a greyish-blue in daylight where synthetic spinel more closely resembles alexandrite with its change from reddish to blue-greenish hues. (There is also genuine color-change sapphire which mimics alexandrite, as well as color-change garnet that can be a real fooler.)
The first thing to do is check the refractive index of the stone, since each material has unique optical properties. Alexandrite, which is a chrysoberyl, is doubly refractive and has an RI near 1.746 (+/-.004) and 1.755 (+/-.005). Corundum is also doubly refractive but has a higher RI, usually near 1.762 and 1.770; spinel's RI is near 1.73 (it varies a bit with different colors) but is singly refractive. A trained gemologist should be able to help you with RI determination.
Genuine alexandrites of about one carat are sometimes (rarely) without eye-visible inclusions, so the fact that you can't see anything in the stone doesn't mean it's not genuine. A look under the microscope at 10X or more is recommended.
Question: I have a ring that was handed down through the family. I was told by a jeweler in Fl that is was a alexanderite. The information I have read on thie alexanderite states that it changes color from green to red. My ring changes from blue to a beautiful purple. This ring is VERY old . I am having it appraised. Could you send me some information on this ring
A large, inclusion-free, color-change alexandrite. Is it real or synthetic?
Answer: The blue to purple color change you describe is indicative of synthetic alexandrite-like (color change) spinel, which has been around for a very long time as an alexandrite simulant. The color change in natural alexandrite is indeed a red to green, usually a darker garnet-type red to a slightly bluish green, if the stone has good color saturation. Another common alex. simulant is the synthetic alexandrite-like corundum (sapphire), which has been around for more than a century and more closely imitates the color of natural alexandrite. Alexandrite is a very, very rare gem. Fine gems of alexandrite over about a carat are rarer still. Most are at least moderately included. If your stone is larger than a carat and has no inclusions, it's almost certainly a synthetic. A gemologist can tell you for sure after examining the stone under the microscope and conducting a simple test of its optical properties, called a refractive index test. .