World's biggest black diamond sold for $4.2M in London

The world's largest cut diamond was sold for more than $4 million at the UK's famous auction house Sotheby's on Wednesday.

The extremely rare diamond, named "The Enigma", was open for bidding from Feb. 3 to 9.

The rare fancy black carbonado diamond weighing 555.55 carats with precisely 55 facets found a buyer who paid £3.16 million ($4.27 million) in cryptocurrency.

"The Enigma" was listed as the world's largest cut diamond by the Guinness Book of World Records in 2006.

Unlike most diamonds formed deep within Earth, carbonados are found in alluvial, sedimentary deposits, close to or on Earth's surface, the auction house explained.

"This, and their specific mineral make up suggest possible extra-terrestrial origins, either from meteoric impacts producing natural chemical vapor deposition or from diamond-bearing asteroids colliding with the Earth," according to the auction note.

The diamond "surpasses the weight of both the Great Star of Africa, 530.2 carats, and the Golden Jubilee, 545.67 carats, making it not only one of the largest fancy black natural-color diamonds in the world, but also the largest faceted diamond to ever appear on the auction market."

Black diamonds are thought to have been formed from a meteoric impact or diamond-bearing asteroid that collided with Earth approximately 3.8 billion years ago, and believed to be a rare natural occurrence only found in Brazil and the Central Republic of Africa.

The auction house had valued for a selling price of £3-5 million.