Why does its color change?
Alexandrite is a variety of chrysoberyl. Its interaction with different light sources can produce green or blue-green tones in daylight and reddish or purplish tones under incandescent light. The change comes from the way the gem absorbs light.
What should you look for?
View the same stone under different light sources. The colors and strength of the change vary, so a screen illustration cannot promise the behavior of an individual gem. Ask whether the stone is natural or laboratory-grown and what documentation is available.
Living with alexandrite
Alexandrite has a Mohs hardness of 8.5 and excellent toughness. Warm, soapy water is a gentle cleaning choice. Discuss the whole piece—including its setting, other gems, and any fracture filling—with your jeweler before using ultrasonic or steam cleaning.
Further reading
GIA: Alexandrite explained ↗GIA: Understanding gemstone and diamond reports ↗GIA: Alexandrite care and cleaning ↗General gemstone education. Individual product disclosures and care instructions should be checked for the piece you choose.