A provided image shows the 555.55-carat black diamond, are "one of the hardest materials known to man." (Photo credit: Provided / Sotheby’s Dubai) ()Black diamonds, also known as carbonado, are extremely rare.
They are found naturally only in Brazil and Central Africa — two regions once connected as part of the supercontinent and believed to have been struck by meteorites, the auction house said.They contain traces of nitrogen and hydrogen that are abundant in interstellar space, as well as osbornite, a mineral uniquely present in meteors.Black diamonds are "one of the hardest materials known to man" and are difficult to cut and polish. "The Enigma – a natural faceted stone of record-breaking size and quality is therefore truly unique, marking an important moment for black diamonds at auction," Sotheby’s said.Other items up for auction have made headlines recently, including a rare copy of the U.S.