Blue diamonds are formed by the concentration of boron in the bonding of atoms. As the amount of boron in a diamond increases so too does the strength of blue. Blue diamonds are almost always type II b, do not contain fluorescence and generally have few imperfections.
Argyle produces another form of blue diamonds of the type Ia type which are sometimes classified as violet by the GIA. These stones share qualities with their argyle pink cousins in that they are generally included and have fluorescence. Their color is caused by the element impurity hydrogen present in their covalent bonding.
GIA grades blue diamonds in terms of tone and saturation. As tone and saturation increase rarity goes up as well as value. Starting from low tone and saturation and increasing GIA grades blue diamonds as light, fancy light, fancy, fancy intense/ fancy deep, and fancy vivid. All categories are very rare and small or large sizes.
The Cullinan mine and Golconda region are the most notable areas where blue diamonds have come from. The most famous blue diamond in history is the 45 carat “Hope Diamond.” In 2008 The Wittelsbach Diamond, a 35.56 carat cushion-shaped fancy deep blue, was purchased at auction for $24 million. Experts compare this stone’s color and characteristics to the famed Hope Diamond.