Home 8 Things to know about Coloured Diamonds 8 Things to know about Coloured Diamonds 1. They’re really rare The Gemological Institute of America estimates that of all the diamonds it sees each year, no more than three percent are coloured. Of these, only five percent are pink diamonds. 2. The world’s most expensive diamond is pink Therefore it comes as no surprise that the most expensive diamond (or jewel) ever sold is The Pink Star, a 59.60-carat Fancy Vivid Pink diamond that reached US$ 71.2million (just over Dhs 260 million) in April 2017 at Sotheby’s Hong Kong. 3. …but the rarest coloured diamonds are red We have yet to see a pure red diamond in a size even close to the 50 carats of the above Pink. These rare gems barely reach over 5 carats; the largest known red diamond is the Moussaieff Red, a 5.11-carat trilliant-cut stone discovered in Brazil. It was rumoured to cost US$ 8million (Dhs 29.3million) in 2002 and would fetch far more than that if it was sold today. 4. Many of the world’s oldest blue diamonds come from India “Golconda diamonds” refer to some of the world’s most beautiful and famous gems that mainly emerged from the "Diamond Capital of India" from the 16th century. Prized for their high transparency and knock-out colours, these gems include Blue diamonds such as the 45-carat Hope and the 31-carat Wittelsbach-Graff. 5. Blue and Yellow diamonds owe their colours to impurities Completely white diamonds are formed of pure carbon and only start to adopt blue or yellow colours when other chemical elements are present. In yellow diamonds this is nitrogen, and in blue diamonds this is boron. 6. But no one really knows what causes colour in pink and red diamonds In comparison to blue or yellow diamonds that owe their colours to these chemical impurities, it is assumed that pink and reds are caused by a mutation that occurs in the diamond's crystal structure as it grows beneath the Earth's surface. 7. Coloured diamonds are really, really old Diamonds are formed under extreme heat and pressure at depths of between 150 and 800km beneath the Earth’s surface. Experts estimate that this process happened up to 3 BILLION years ago (or 1 billion if you have a younger diamond) before they travelled to the surface in volcanic eruptions. That’s a whole lot of history to wear on your finger. 8. Their colours can be treated The diamonds mentioned here all owe their colours to the earth’s natural processes. However, diamonds can be treated by either heating or irradiation to produce some of these colours. There is nothing wrong with this, as long as the information is properly disclosed – so always ask before you buy.