1. I. S. M. Ramsey, Phys. Rev.,77, 567 (1950);78, 699 (1950).
2. F. K. Chukhrova (editor), In handbook: Minerals [in Russian],2, No. 1, pp. 63, 75; Izd-vo AN SSSR, Moscow (1963).
3. B. V. Beznosikov and N. V. Beznosikova, Kristallograflya,18, 1, 188 (1968).
4. V. S. Grechishkin and M. L. Zlarogorskii, Fiz. Tverd. Tela,4, 1238 (1964).
5. H. S. Gutowsky, D. W. McCall, B. R. Garvey, and L. H. Mayer, J. Amer. Chem. Soc.,74, 4809 (1952).