1. Posner, A. S., Perloff, A., and Diorio, A. F., Acta Cryst., 11, 308 (1958).
2. Mitchell, L., Faust, G. T., Hendricks, S. B., and Reynolds, D. S., Amer. Mineralogist, 28, 356 (1943).
3. Kay, M. I., Fraser, B. C., and Ueda, R., Acta Cryst., 15, 506 (1962).
4. Busing, W. R., Martin, K. O., and Levy, H. A., ORNL–TM–305 (1962).
5. International Tables for X-ray Crystallography, 1, Space Group 176 (Intern. Union Crystallography, 1952).