Black 555.55-carat Formed 2 Billion Years Ago Sells For $4.28 Million At Auction (Photos)

A rare black 555.55-carat diamond dubbed 'The Enigma' that formed 'when an asteroid hit Earth more than 2.6 billion years ago' had sold for £3.1 million ($4.28 million) at auction. The 555.55-carat was bought by Richard Heart, founder of cryptocurrency company Hex and the diamond is regarded as the world's largest known cut diamond.

Richard Heart said he was renaming the rock as the 'Hex.com diamond'.

Heart tweeted: 'I won the world's largest cut diamond for our #HEXican cultural heritage! 'It'll be called the HEX.com diamond, it weighs 555.55 carats and has 55 facets. Congratulations to all you #HEXicans.'

The rock is considered extremely heavy for a diamond. It is a carbonado, an extremely rare rock that has only ever been discovered in Brazil and the Central African Republic, and is one of the toughest forms of natural diamond.

Following the auction, auction house Sotheby's tweeted: '"The Enigma": This 555.55 carat Black Diamond sold today for £3,161,000 / $4,292,322.

'The buyer has opted to use cryptocurrency for the purchase.'