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The Blue Moon Diamond

By  , Wednesday, October 21, 2015

The Hope Diamond is the best known fancy blue diamond in the world, and while nowhere near the biggest diamond ever found, it is arguably the most famous diamond in history. Fancy blue diamonds of any size are exceedingly rare in nature. But the recently discovered Blue Moon Diamond has attributes that even the Hope cannot claim!


The 12-carat, Internally Flawless, Fancy, Vivid Blue Moon Diamond.

Copyright: Cora International. Photo by Tino Hammid.


The gem, cleverly named “Blue Moon” for both its color and rarity, was polished out of a 29.62-carat rough diamond found by Petra Diamonds Ltd. at the Cullinan mine in South Africa. Cora International, a New York-based gem cutter, purchased the diamond and took more than six months to cut and polish the stone which finished at just over twelve carats.


Sotheby’s plans to auction the diamond which it estimates may be worth 34 million Swiss francs ($35 million). That would break the record for a stone of that hue. The highest price for a blue diamond sold at auction to date was the 9.75-carat “Zoe Diamond” which went for $32.6 million in New York in November 2014. The 12.03-carat Internally Flawless Blue Moon diamond, which has the highest possible color grade of fancy vivid blue, will be the star attraction in a Sotheby’s auction in November in Geneva, Switzerland.


Blue diamonds are formed when boron mixes with carbon as the gem crystalizes almost 100 miles beneath the Earth’s crust. The boron atoms in the carbon lattice create “color centers” that sometimes result in blue coloration. Less than one boron atom per million carbon atoms can sometimes result in a fancy blue.


While the Hope diamond at 45.52ct is considerably larger, the Blue Moon is graded much higher in color and clarity. The Hope has some white graining that drops its clarity to VS1 (three grades lower than Blue Moon) and the color is fancy dark grayish blue, not as pure a hue as the Blue Moon’s fancy vivid blue. The grading of natural fancy color diamonds takes into account hue, saturation and tone. The ultimate color grade for a blue diamond is fancy vivid blue. The Blue Moon also has the benefit of a more modern cut, although it shares the basic cushion shape of the Hope.


The 12-carat, Internally Flawless, Fancy, Vivid Blue Moon Diamond.

Copyright: Cora International. Photo by Tino Hammid.


Both of these historic diamonds share another unique attribute. While about 30% of all diamonds exhibit fluorescence, these two diamonds have a rare property known as phosphorescence. When exposed to ultraviolet light (UV), both diamonds fluoresce red and continue to emit a red glow for a period of time after the UV is turned off. Fluorescent diamonds will glow only as long as they are exposed to the UV light.


The public has a unique opportunity to see the Blue Moon diamond which will be on display at the Natural History Museum of Los Angeles County until January 6, 2016. 


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