1. Estimated from data of E. Chin; in Minerals Year Book 1972, Vol. I, U.S. Bureau of Mines, p. 743.
2. L. M. Pidgeon and W. A. Alexander, Trans. AIME 159(1944), 315-52, also other papers in this volume, 353-391.
3. F. Trocine, in Advances in Extractive Metallurgy and Refining, M. J. Jones, Ed., Inst. Min. Met. (London), 1972, 517-20.
4. J. R. Wynnyckyj and L. M. Pidgeon, Met. Trans. 2(1971), 979-86.