Glossary
Montana (USA)
Montana is the most important sapphire source in the United States. The best known are the sapphires from Yogo Gulch, which has been mined on and off since the late 19th century.
Yogo sapphire
Yogo sapphires show a clear blue to lilac without colour zoning and are regarded as naturally untreated. The crystals are flat; cut stones above one carat are rare.
Other deposits
Rock Creek and the Missouri River yield sapphires in many colours, which are usually heated.
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Updated 2026-10-06