1. P. T. B. Shaffer,Acta Cryst. B25 Part 3 (1965).
2. A. R. Verma andP. Krishan, ?Polymorphism and Polytypism in Crystals? (J. Wiley, New York, 1966).
3. J. R. O'Conner andJ. Smiltens, ?Silicon Carbide? (Pergamon Press, Oxford, 1960).
4. P. L. Farnsworth andR. L. Coble,J. Amer. Ceram. Soc. 49 (1966) 264.
5. T. D. Gulden,ibid 52 (1969) 585.