Art house 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. 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 carbonado, one of the toughest forms of natural diamond. It contains osbornite, a mineral found only in meteors, which makes 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. The precise origin of black diamonds remains a mystery. They are estimated to be around 2.6 to 3.2 billion years old – a time before dinosaurs existed.