New Lead Silicates: Structures and Topology and Symmetry Analysis

Crystals of a new complex layered lead carbonate silicate Pb 19.4 Na 1.9 [Si 10 O 25 ](CO 3 ) 9 (OH) 12.7 ⋅ 1.3H 2 O and lead silicogermanate Pb 4.37 [(Ge 0.7 Si 0.3 ) 2 O 7 ][(Ge 0.6 Si 0.4 )O 2.74 (OH) 1.26 ], related to ganomalite, were prepared by the hydrothermal synthesis route. The compounds crystallize in sp. gr. P 31 m and P 6̅ , respectively. The new compounds, like many lead silicates and silicogermanates, are characterized by disorder, wide isomorphism, defects at sites occupied by large cations, and isomorphous substitutions of Ge and Si atoms in tetrahedra. The similarity and difference of new lead compounds compared to those studied previously were revealed in terms of the traditional crystal-chemical theory and the topology and symmetry analysis of structures. The structural relationships `for the plumbonacrite–new carbonate silicate–synthetic lead borate silicate and apatite–nasonite–ganomalite–synthetic lead silicate series are described. The polytypic nature and homologous series were revealed. The alphabetic notation is proposed to describe the symmetry laws of structures.