Why Sri Lanka's 'Star of Pure Land' sapphire is unique?

The 3,563-carat Star of Pure Land sapphire, discovered in Sri Lanka, is special because of its rare purple colour and its clear six-ray star pattern, known as asterism. It is sharp, well-centred and evenly formed, which is uncommon in natural sapphires. Experts say its clarity, natural formation and strong star effect place it among the rarest star sapphires ever found.