| All coloured diamonds contain interstitial impurities or structural defects that cause the colouration. Pure diamonds are transparent and colourless. Type IIa diamonds can be coloured pink, red, or brown due to structural anomalies caused through plastic deformation during crystal growth. Type IIb diamonds, which account for 0.1% of gem diamonds, are usually light blue due to scattered boron within the crystal matrix; these diamonds are also semiconductors, unlike other diamond types. A blue-grey color may also occur in Type Ia diamonds and be unrelated to boron. |  |
 | While very rare, blue diamonds are not the rarest. They are more uncommon than yellow diamonds, which have nitrogen in them, but they lose out in rarity to green, black, pink, orange, purple, and red.  |  |
 | The Hope Diamond is 45.52 carats and is the largest deep-blue diamond known. The stone can be traced to Golconda and is considered by many to be the most famous diamond in the world. Now on permanent display at the Smithsonian Natural History Museum in Washington, D.C. It is a Type IIb diamond and exhibits red phosphorescence after exposure to ultraviolet light. The diamond is notorious for supposedly being cursed. |  |
 | The Wittelsbach-Graff is a 31.06-carat, Fancy Deep Grayish Blue diamond with an IF clarity and an unusual cut with 82 facets. The stone sold in 2008 for $24.3 million. |  |
 | The Blue Empress is a spectacular 14 carat, symmetrical pear-shaped, fancy vivid blue diamond. The stone was mined at the Premier Diamond Mine in South Africa and was purchased from De Beers by the Steinmetz Group. It was first offered for sale by London’s Harrods in 2003 for £10 million. |  |
 | 13.22 carat pear-shaped Fancy Vivid blue flawless diamond sold at Christie's Geneva on May 14, 2014 for $ 24m, setting a new world auction record for the price per carat for a blue diamond. Immediately after the sale, it was renamed 'The Winston Blue'. |  |
 | On October 8th, 2007 a 6.04 carat Fancy Vivid Blue diamond set in a platinum ring, flanked by two white emerald-cut diamonds sold for $7.98 million This 7.03-carat blue diamond sold for $9 million at the Sotheby’s. |  |
 | The Premier Blue is a 7.59-Carat Internally Flawless Fancy Vivid Blue Diamond. Expected to bring upwards of $ 19m the stone did not change hands in late 2013. |  |
 A 6.01 carat Fancy Vivid Blue Diamond that sold for $10.1 million, or $1,686,505 per carat, at Sotheby’s Hong Kong in October 2011. |
 US$1.59 million per carat was achieved by a 8.01-carat, emerald-cut, fancy vivid blue diamond in 2012. |  A 5.3 carat blue diamond fetched $9.6 million, or $1.8 million per carat in April 2013. |
 The flawless "Blue Moon Diamond", which weighs 12.03 carats could fetch $35-55 million at auction next week |  |
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