Auctioneer Sotheby’s just sold off a billion-year-old black diamond for $4.3m. The 555.55-carat gem named The Enigma is believed to be the world’s largest cut diamond. It weighs about the same as a banana. It had been expected to fetch more than $5m when it went on sale in an online auction. There are debating theories about the origins of the stone, including that it was carried to Earth by an asteroid. Its new owner is entrepreneur Richard Heart who purchased it using cryptocurrency. He told his more than 180,000 Twitter followers that “as soon as the payment’s gone through and possession’s been taken” the gem would be renamed the “ diamond,” in honor of the blockchain platform he founded.

The gem is a member of the carbonado family, one of the toughest forms of natural diamond. Due to its traces of osbornite, a mineral found only in meteors, many scientists believe that Enigma originated from space. Carbonados are extremely rare and have been discovered in only two regions of the world—Brazil and the Central African Republic. Sotheby’s described it as “one of the rarest, billion-year-old cosmic wonders known to humankind.” The precise origin of black diamonds remains to be a mystery. Black diamonds are estimated to be around 2.6 to 3.2 billion years old – a time before dinosaurs existed.