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The changing color of U.S. sapphires.
Colored Stone 1993 Jan-Feb; 6(1):370-371
The production of gem-quality sapphire has greatly increased in the United States. The commercial production is from three areas in Montana: Yogo Gulch, Rock Creek, and the Missouri River. Development of technology for heat-treatment of Montana sapphires has enhanced not only their value, but their acceptance by the gem industry.
Mineral deposits; Mineral processing; Minerals
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Page last reviewed: May 5, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division