A rare square 37-carat emerald owned by the Aga Khan fetched nearly $9 million at auction in Geneva on Tuesday, making it the world's most expensive green stone.

A rare square 37-carat emerald owned by the Aga Khan fetched nearly nine million dollars at auction in Geneva on Tuesday, making it the world's most expensive green stone.

The Aga Khan emerald has sold for $AU13.4 million at an auction in Geneva. The 37-carat gem was a gift from the Aga Khan Prince to his wife, Nina Dyer, in 1960, just five years before her death at age 30.