Alexandrite

These are the most exclusive and expensive among all the gems found on earth. They are also the rarest. Only Diamonds can second them. They are very exclusive due to it’s little availability. 

Reason is they are discovered at a ratio of 1% to all the other rare gem finds. Even within that discovered Alexandrites , gems of highest quality are even rare. These belong to gem family known as chresoberils. They have a density of 8.5. These have a special behavior that cannot be seen in other gem types. Alexandrites glow in emerald green at day light and glow in red at night. 

They get this ability from chromium molecules in it. Best quality alexandrites are found in gem mines located in Ratnapura , Pelmadulla and Kahawatta. These types of gems can be found in India and Madagascar but in lesser quality. Sri Lankan Alexandrites do not contain FE (Iron) in them , but others do. Therefore non-sri lankan alenxandrites don’t have the dual color effect. You must be very careful when purchasing Alexandrites. Highest Quality Alexandrites are readily available in Sri Lanka only.