The Yogo sapphire comes from Montana in the USA. These are a variety of sapphires (corundums) that are only found in the Yogo Gulch. Tiffany declared them "the finest gems ever found in the United States". The Yogo sapphire is considered the only "untreated" sapphire in the world. Indeed, 95% of the sapphires in the world have been heat treated to improve their natural color. Diams SA works with one of the few companies that still operates the Yogo sapphire.