|The Shirley Temple Blue Diamond A 9.54-carat Fancy Deep Blue, Potentially Internally Flawless, VVS2 clarity diamond ring|
Of all the naturally colored diamonds, blue diamonds are among the rarest. Their color is caused by the presence of boron impurities and according to the GIA, the more boron - the deeper the blue.
Blue diamonds are highly coveted, and some blues have fetched staggeringly high prices at auctions in recent years. For instance, In April 2016, a 10.10 carat oval-shaped fancy vivid blue diamond broke all auction records in Asia when it was sold by Sotheby’s for $31.8 million.
In August 2014, an exceptionally rare blue diamond, called the 'Blue Moon', surprised even the curator of the National Gem and Mineral Collection at Washington, D.C.'s Smithsonian Institution, when under ultra-violet light, it emitted an orangey-red phosphorescent glow for about 20 seconds. Usually, a blue diamond will glow in a blue-green color for less time, but the “Blue Moon” showed its purity being un-muddled by the presence of grey or other hues. The 29.62-carat stone was discovered at South Africa's Cullinan mine and bought by Cora International, who had it cut and polished.
In the first quarter of 2016, fancy blue diamond prices rose by 1.7% - the highest increase among naturally colored diamonds. The strongest performing price categories were fancy intense blue and fancy vivid blue across all carat sizes.