The Zoe Diamond

In 2014 the collection of Rachel Mellon, wife of the late philanthropist Paul Mellon, came up for auction at Sothebys. The pinnacle of the collection, and most sought after by potential buyers, was the Zoe diamond. This particular stone was classified as a 9.75 carat fancy vivid blue diamond. Originally believed capable of fetching around $15 million, the Zoe diamond shocked everyone when the winning bid came in at $32.6 million. This makes the Zoe diamond not only the most expensive blue diamond in the world, but also the most expensive diamond in terms of pricepercarat ($3.3 million).