Alexandrite is a variety of chrysoberyl.
The most striking characteristic of this gem and that gives it more value is that it has a different color depending on whether it is given natural or artificial light: green under daylight and purple-red under incandescent artificial light.
In the photo we can see its red fluorescence under long wave UV light.
Most Common Activator: Cr3+
Other activators: Mn4+ , V2+ ,