1. L. Brewer et al.: Chemistry and Metallurgy of Miscellaneous Materials. Chap. 4 (1950) New York. McGraw Hill Book Co.
2. J. S. Brown: Ore Genesis. (1948) Hopewell Press.
3. K. K. Kelley: U. S. Bur. Mines Bull. 383 (1935 61.
4. V. R. Schenck and A. Albers: Ztsch. anorg. allgem. Chem. (1919) 105, pp. 145–146.
5. B. K. Veselovskii: Journal of Applied Chemistry (Russian) (1942) 15, pp. 422–435.