1. N. A. Toropov and I. A. Bondar', Izv. AN SSSR. Otd. khim. n.1959. 554; I. A. Bondar', Collection: The Chemistry and Practical Use of Silicates [in Russian] (Leningrad, 1960) pp. 5?9.
2. I. Warshaw and R. Roy. Am. Ceram. Soc. Bull.38, No. 4, 169 (1959).
3. W. L. Wanmaker, W. P. deGraaf, and H. L. Spier, Physica25, No. 11, 1125 (1959).
4. Alphabetical and Numerical Indices of X-ray Diffraction Patterns (ASTM, 1953).
5. B. F. Ormont, The Structure of Inorganic Substances [in Russian] (Moscow-Leningrad, 1950) p. 455.