A billion-year-old black diamond, believed to be the largest cut diamond on Earth, is going up for auction. There are competing theories about the origins of the gem, named The Enigma, including ...

A billion-year-old black diamond, believed to be the world's largest cut diamond, has sold for £3.16m ($4.3m). Named The Enigma, the 555.55 carat gem, which weighs about the same as a banana ...