1. E.A. Ingerson, G.W. Morey, Am. Miner. 36, 778 (1951)
2. R. Hodenberg, G. Struensee, Ns. Jb. Miner. Monatsh. 3, 125 (1980)
3. A.V. Novoselova, A.S. Pashinkin, K.N. Semenenko, Bull. Moscow Univ. (in Russian) 3, 49 (1955)
4. N.K. Bel’skiy, Dokl. Acad. Sci. USSR (in Russian) 143, 1313 (1962)
5. E. Staritzky, A.L. Truitt, in The actinide elements, ed. by G.T. Seaborg, J.J. Katz, (McGraw-Hill, New York, 1954)