A golden-hued diamond brooch, similar to one worn by the late Queen Elizabeth, is expected to be sold for around $6 million at a Sotheby's auction in Geneva this week.

The "Allnatt" diamond, bearing the name of its first owner, a British sportsman, is a rare stone, fancy vivid yellow in colour and weighing 101.29 carats.

It was mounted by Cartier into a floral design strongly resembling Queen Elizabeth's Williamson Pink diamond, given to her as a wedding gift in 1947.

An unmounted, internally flawless diamond weighing over 37 carats will also come up for sale at the same auction on Tuesday, Sotheby's said.