Natural Blue diamonds are so rare. This blue diamond is enhanced and treated. The treatment can only work with a small minority of diamonds, and involves irradiating them causing the colour change, usually followed by heat treatment to stabilise the colour.
Sotheby's flawless Blue Moon diamond, a 12.03ct will be the largest ever blue diamond ever to appear at auction. It was cut from a 29.62 rough blue, found by Petra Diamonds at the South African Cullinan mine in Jan 2014. It was purchased by Cora International and took 6 months to cut and polish. Estimates for auction will be between $35 and $55 million.