1. USGS mineral commodity summaries (2012)
2. http://www.webelements.com/
3. http://www.chemicool.com/
4. B.A. Wills, Mineral Processing Technology, 3rd edn. (Pergamon Press, Oxford, 1985)
5. W. Dennen, M. Resources, Geology Exploration, and Development (Taylor & Francis, New York, 1989)