Alexandrite

Alexandrite is a gemstone. It is a type of chrysoberyl. Different kinds of light make the colors change. That is called the "alexandrite effect". 
A gemstone similar to alexandrite can be made in a laboratory. That kind of stone is called synthetic or simulated alexandrite. These are not made of chrysoberyl. People make these because alexandrite is expensive, and the synthetic alexandrite costs less.
One story says that alexandrite was named in honor of Alexander II of Russia. Alexander was not yet Tsar at the time.
Alexandrite has been found in Russia, Brazil, India, Madagascar and Sri Lanka.
Alexandrite is one of the birthstones for June.