Star of India
At 563 carats, the Star of India is the world's largest gem-quality blue star sapphire. Some 2 billion years old, it is also one of the most well-known objects in the world.
Rutile, a mineral in the Star of India, gives the gem its milky quality and star effect. Tiny fibers of rutile in a three-fold pattern reflect incoming light in the star pattern. This effect, called asterism, makes this gem a true star.