The Enigma: Billion-year-old black diamond “from space” up for auction

The gem, known as The Enigma, is believed to be the largest cut diamond on Earth.

Little is known about the history of the 555.55 carat black diamond now up for auction.

There are competing theories about the origins of the gem, including that it came from space.

At 555.55 carats the gem is considered extremely heavy for a diamond, weighing about the same as a banana.

The rock is expected to fetch over £4.4 m ($6m) at a Sotheby's auction in London by the time online bidding closes next week.

The gem is a carbonado, one of the toughest forms of natural diamond.
Black diamonds are usually about 2.6 to 3.2 billion years old - a time before dinosaurs existed.

The Earth itself is around 4.65 billion years old, so not much older than black diamonds.

Carbonados are extremely rare and have only ever been discovered in Brazil and the Central African Republic.

Because they contain osbornite, a mineral found only in meteors, they are believed to originate from space.