The U.S. Geological Survey is grateful to the following individuals for
their assistance:
Harvey E. Belkin, Geologist, Geological Survey, U.S. Department of the
Interior, Reston, VA.
Gordon T. Austin, “Gem Stones,” _Mineral Commodity Summaries 1991_,
Bureau of Mines, U.S. Department of the Interior, Washington, DC.
Robert E. Thaden, “Gem Stones,” in _United States Mineral Resources_,
Geological Survey Professional Paper 820, U.S. Government Printing
Office, Washington, 1973, p. 247-250.
Jane Jenness, Minerals Information Office, U.S. Geological Survey,
Washington, DC.