Acknowledgments
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.