The Aga Khan emerald, the world's most expensive green stone, fetches $9 million at auction

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

Sold by Christie's, the Cartier diamond and emerald brooch, which can be worn as a pendant, is a piece of jewelry made by the fashion house Bulgari, which Richard Burton gave as a wedding gift to his fellow actress. Elizabeth Taylorlike the most precious emerald.

In 1960, Prince Sadruddin Aga Khan commissioned Cartier to set an emerald in a marquise-cut 20-diamond brooch for British socialite Nina Dyer, to whom he was briefly married.

Dyer then sold the emerald to raise money for the animals in 1969.

Luckily that was Christie's first sale in Switzerland on the shores of Lake Geneva, where the emerald found its way back to the 110th edition this year.

It was bought by jeweler Van Cleef & Arpels before passing a few years later into the hands of Harry Winstonnamed “King of Diamonds.”

“Emeralds are hot right now, and this one ticks all the boxes,” said Christie's EMEA Head of Jewelery Max Fawcett. “…We might see an emerald of this quality come up for sale once every five or six years.”

Also set with diamonds, the former record holder fetched $6.5 million at an auction for part of Hollywood legend Elizabeth Taylor's famed jewelry collection in New York.