The Logan Sapphire Brooch, National Museum of Natural History, Washington, D.C.
The Logan Sapphire is a flawless specimen from Sri Lanka, a cushion-cut stone which possesses a rich deep blue color and is the second largest (blue) sapphire known, weighing 422.99 carats (84.6 g).
The stone, roughly the size of an egg, is one of the world's largest and most famous sapphires. The Logan Sapphire is named after Polly Logan, who donated the gemstone to the Smithsonian Institution in 1960.
The Logan Sapphire is set in a brooch surrounded by 20 round brilliant cut diamonds weighing, in total, 16 carats (3.2 g). It is currently on display at the National Museum of Natural History in Washington, D.C., alongside the Bismarck Sapphire Necklace and the Hall Sapphire and Diamond Necklace.