This blue diamond may become the most expensive gem ever sold at auction

The diamond’s name makes reference to the idiom “once in a blue moon,” as is very rare to find one of that shade and clarity.

A rare 12-carat, flawless blue-coloured diamond, known as Blue Moon, may soon become the most expensive gem ever sold at an auction as it is expected to fetch up to $55 million when it goes under Sotheby’s hammer on Nov. 11, in Geneva.

To set the world record price for any diamond put to auction, Blue Moon must sell for more than $46.2 million, which is what The Graff Pink went for in 2010.

If it does fetch over that price, the South Africa-mined rock would also be the most expensive blue rock ever sold, beating the Zoe Diamond, which fetched $32.6 million in 2014, international auction house Sotheby’s said.

The rock was found by Petra Diamonds at the Cullinan mine in South Africa.

Blue Moon was polished out of a 29.62-carat rough diamond found by Petra Diamonds (LON:PDL) at the Cullinan mine in South Africa. Cora International, a New York- based gem-cutter, purchased the rock and took more than six months to prepare the stone.

Its name is a reference to the idiom “once in a blue moon,” a hat tip to the rarity of finding a diamond of that shade and clarity, Sotheby’s said.

All images courtesy of Sotheby’s.