This gemstone is actually another form of Chrysoberyl, which is a gem family I was talking about a few months ago, and its physical properties are very similar.
What sets it apart is the fact that it appears green in natural sunlight and red in incandescent light.. One of the most dramatic examples of colour change you will find in gems.
All stones are natural and available for sale from Tsarstone Collectors Guide
It was first discovered in Russia and named after Czar Alexander II. It is one of the rarest and gems of high quality are the most expensive of all the gemstones. (yes including diamonds)