1. The elements;Hale,1962
2. Columbium and Tantalum. A Materials Survey;Barton;U.S. Dept. Interior, Bureau of Mines, Circ. No. 8120,1962
3. A Smaller Classical Dictionary,1926
4. Principles of Geochemistry;Mason,1958
5. Spectrochemical Analysis;Ahrens,1950