1. Arem, J. E. 1987. Color encyclopedia of gemstones. 2nd ed. New York: Van Nostrand Reinhold.
2. Bauer, M. 1904. Precious stones. English ed. London: Charles Griffen & Co.
3. Schumann, W. 1997. Gemstones of the world. New York: Sterling Publishing.
4. Wise, R. W. 2003. Secrets of the gem trade: The connoisseur's guide to precious gemstones. Lenox, MA: Brunswick House Press.