The blue diamond adopts its luxurious colour at an early stage, when boron first appears. The more boron, the more intense the colour. Very occasionally, due to the additional presence of hydrogen a greyish blue appears.

Blue diamonds generally come from South Africa, while a small number of deep blue diamonds are found in Central Africa, Brazil & Borneo. Historically, blue diamonds have been found in India and metallic blue diamonds have been found in the Argyle mines in Australia. In November 2014, a 9.75 carat blue diamond, the Mellon Blue, sold for a staggering $32.6 million at Sotheby’s in New York, before being renamed the Zoe Diamond.