The royal family has decided to leave the 105-carat gem out of this weekend's coronation ceremony. The Koh-i-noor has become a focus of anti-colonial anger. India wants it back.

NPR ventures into a Colombian emerald mine — which used to be more dangerous, with potential explosions inside and gunfights outside. The CEO, a former U.S. diplomat, says he wanted to change that.

The "Americus Australis" gem weighs more than 11,800 carats and is one of the largest gem-quality opals in existence. It also has a long history.