1. F. Hulliger, Struct. Bonding
4 (1968), 83.
2. R. Ballestracci and E. F. Bertaut, Bull. Soc. Fr. Mineral.-Cristallogr
87 (1964), 512.
3. R. Ballestracci, Bull. Soc. Fr. Mineral.-Cristallogr
88 (1965), 207.
4. M. Tromme, Compt. Rend. Acad. Sci
273 (1971), 849.
5. W. Bronger, R. Elter, E. Maus, and T. Schmitt, Rev. Chim. Miner
10 (1973), 147.