1. cf. Liebau, F., Reviews in Mineralogy Vol. 5. Orthosilicates, (Editor P.H. Ribbe, Mineralogical Society of America, 1980) Chap. 1.
2. Hoebbel, D., W. Wieker, P. Francke and A. Otto, Z. Anorg. Allg. Chemie 418, (1975) 35.
3. Liebau, F. and I. Pallas, Z. Krist. 155, (1981) 139.
4. Ref. 1, p. 9.
5. Ref. 1, p. 10.