1. and , The Larousse Encyclopedia of Precious Gems, translated into English by Van Nostrand Reinhold, New York, 1992, p. 58.
2. Gemstones with Alexandrite Effect
3. The optical spectra and color of chromium containing solids
4. The Physics and Chemistry of Color–The Fifteen Causes of Color, John Wiley & Sons, New York, 1983, p. 89.