1. Beckmann, J. 1799,Marbodi liber lapidum seu de gemmis,J.C. Dieterich, Gottingen.
2. Bostock, J., and Riley, H. T. 1857,The natural history of Pliny:H.G. Bohn, London.
3. Deer, W. A., Howie, R. A., and Zussman, J. 1992,An introduction to rock forming minerals: Longman Scientific & Technical.
4. Evans, I. H. 1970,Brewers dictionary of phrase and fable: Cassell, London.
5. GIA 1995,Gem reference guide, Gemmological Institute of America, CA, USA.