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 ...

There was a time when a moral ... but we could not do without our coals. The Koh-i-Noor diamond is valued at $2,500,000—a sum which could purchase 590,000 tons of coal. If this diamond was ...

and "What are those black diamonds for?" The answer to the first ... help you find multiple studs in a wall without making ...

There's a huge demand for black opal, with lack of supply driving ... 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 ...