Sotheby’s auctioned the gem in 2011, and it was sold to an unknown buyer, setting a record for the most expensive yellow diamond ever sold. The original 241-carat rough stone was discovered in ...

Narrator: High-quality black opal can cost over $10,000 per carat, making it one of the world's most expensive gemstones. But mining black opal isn't easy. After investing tens of thousands of ...