1. R. C. Schoodde, Recent trends in mineral explorations-are we finding enough?. http://www.minexconsulting.com/publications/nov2011.html . Cited April 29, 2015.
2. Study on Critical Raw Materials at EU Level: Final Report 2013 (2013).
3. T. E. Graedel, R. Barr, T. E. Chandler, et al., “Methodology of metal criticality,” Environ. Sci. Technol. 46, 1063 (2012).
4. Minerals, Critical Minerals, and the U.S. Economy (National Academy Press, Washington, 2008).
5. US Industrial College of Armed Forces: Spring Report 2012 (2012).