1. Gastuche, M. C., and Herbillon, A., Bull. Soc. Chim. Fr., 1404 (1962).
2. Saalfeld, N., Neues Jb. Miner. Abh., 95, 1 (1960).
3. Atkinson, R. J., Posner, A. M., and Quirk, J. P., J. inorg. nucl. Chem., 30, 2371 (1968).
4. Atkinson, R. J., Posner, A. M., and Quirk, J. P., J. inorg. nucl. Chem., 34, 2201 (1972).
5. Bragg, L., and Claringbull, G. F., The Crystal Structures of Minerals. (Bell, London, 1965).