The 555.55 carat black diamond has belonged to its current owner for two decades but little is known about its history before that. A billion-year-old black diamond, believed to be the world's ...

But the cost could rocket if new rules aimed at stopping the trade in Russian diamonds come into force early next year, experts have warned. A typical ring is worth between £1,900 and £2,000.

Black opal costs from $1,000 a carat to tens of thousands ... In the '80s and '90s, gem-quality brown diamonds were worth about $1,500 per carat, but now many sell for up to $10,000 per carat.

The 555.55 carat black diamond has belonged to its current owner for two decades but little is known about its history before that. A billion-year-old black diamond, believed to be the largest cut ...