1. Beck, M. T.: 1978 in Sigel, H. (ed.),Metal Ion in Biological Systems, Marcel Dekker, New York, Vol. 7, p. 1.
2. Bernal, J. d.: 1951,The Physical Basis of Life, Routledge and Kegan Paul, p. 34.
3. Bodenheimer, W. and Heller, L.: 1967,Clay Minerals 7, 167.
4. Dolezal, J. and Kourim, V.: 1969,Radiochem, Radioanal. Lett. 1, 295.
5. Egami, F.: 1974,J. Mol. Evol. 4, 113.