The Secret Behind The Blue Moon Diamond's Multi-Million Dollar, Ocean-Like Hue

Everyone is gushing over the Blue Moon diamond, a jewel that is set to become the world's most expensive.

That is, if it can fetch the $46.2 million price tag Sotheby's is hoping for, CNBC reported. That question will be answered this fall, when it goes on the auction block in Switzerland.

The Blue Moon diamond was discovered in January 2014 at a mine in South Africa called the Cullinan Mine. When it was plucked from the ground, it was 29.62 carats in its rough form, the Daily Mirror added.

Cora International, based in New York, bought the jewel and took six months to cut and polish it to its current 12-carat cushion shape; it's the largest of that style to ever appear at auction.

Its rarity has inspired plenty of hype since it was found, and the chairman of Sotheby's jewelry division, David Bennett, said the hype is "totally justified." He can't stop gushing over the stone, calling it "simply sensational."

"Weighing in at 12.03 carats, (it) is a simply sensational stone of perfect colour and purity, combined with a superb cushion shape. Blue, for me, is the most mysterious and magical of all the colours of diamond, and the Blue Moon will now take its place among the most famous gems in the world."

In fact, the diamond's name is a tribute to that rare beauty, taken from that oft-repeated idiom.

But it's also officially perfect -- the Gemological Institute of America has declared it "internally flawless" and given it a rating of Fancy Vivid Blue, which is pretty much the highest grade one can hope for.

So where exactly does this lovely hue come from? It's all a matter of atoms.

According to Quartz, diamonds are usually clear because they're made of carbon, which is colorless. When the gem is colored, that's a sign that some other ingredient got into the mix or the structure was damaged, and often that makes it less valuable. But when those impurities give the diamond a deep color -- rather than make it muddy -- that's when it becomes as rare as the Blue Moon.

In this jewel's case, boron has taken the place of some of the carbon atoms in its lattice-like structure. This makes it absorb red light; therefore, white light passing through a diamond containing boron comes out blue. But this isn't the rarest color -- pink and red earn that title. It's believed that the stress of being pushed up through the earth damages the structure, giving it that rarest of hues. Green, black, orange, and purple are also rarer than that pretty ocean-colored tint.

In fact, one of those much-rarer pink diamonds currently holds the record for the world's most expensive. It was called the Pink Graff and sold in 2010. Before the Blue Moon Diamond goes on the auction block on November 11 in Geneva, it'll make appearances in Hong Kong, London, and New York, the Local added.

Click here for photos of the gem.

[Photo Courtesy YouTube Screengrab / Sotheby's]