| , 1980, Gems Made By Man, Gemological Institute of America,• Elwell-Center for materials Research Stanford University-first published in 1979 by Ellis Horwood Limited England- p 158• | Karl Schmetzer, Dietmar Schwartz, Heinz-Jurgen Bernhardt, Tobias Hager Journal of Gemmology of Gemmological Association of Great Britain, September, Vol |
|---|---|
| , edited by William Crooke; Vol | Read, Peter 2008 Gemmology 3rd rev |
Brunswick House Press ; p.