1. G. Bergerhoff, W.H. Baur, W. Nowacki, N. Jb. Miner. Mh. 193 (1958)
2. R.M. Barrer, J.W. Baynham, F.W. Bultitude, W.M. Meier, J. Chem. Soc. 195 (1959)
3. R.M. Milton, U.S. Patent 2, 882, 244 (1959)
4. W.H. Baur, Am. Mineral. 49, 697 (1964)
5. D.W. Breck, U.S. Patent 3, 130, 007 (1964)