1. London;Cruickshank;Chem Soc,1961
2. Frank Pietrowski and Wolfram Priess Minerai;Jost;Acta Crystallogr Bull Soc Fr Christallogr,1969
3. to be published , for technical details see Vogel and Theochem;Wolff;Mol Struct,1989
4. Non;Binks;Cryst Solids,1980