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The world's largest known cut diamond has gone on display in Dubai, ahead of its predicted big money sale.

The black diamond - which is called 'The Enigma' - is billions of years old.

It's believed to have formed when a meteorite hit the Earth 2.6 to 3.8 billion years ago.

This is the first time the stone has been shown to the public as its owner has been keeping it tucked away for more than two decades.

Black diamonds like these are really rare. As the name suggests they appear dark and opaque.

They were first discovered in 1841 by a group of Portuguese explorers in Brazil who called them 'carbonado' because they look like pieces of charcoal.

Experts predict that the diamond could sell for more than £5m at the auction at Sotherby's Dubai in February.

The auction house plans to accept cryptocurrency as a form of payment for the diamond.

Sophie Stevens, a jewellery specialist at the auction house said that the The Enigma is likely to be from space.

"We believe that they were formed through extra terrestrial origins, with meteorites colliding with the Earth and either forming chemical vapour disposition or indeed coming from the meteorites themselves," she said.

The special stone contains traces of the gases nitrogen and hydrogen, which are very common in space. It also contains traces of a mineral called Osbornite, which is unique to meteors.