Crystal structure of yegorovite Na4[Si4O8(OH)4] · 7H2O

Using X-ray analysis, the crystal structure of yegorovite Na4[Si4O8(OH)4] · 7H2O, a newly-discovered mineral from the Lovozero alkaline complex (Kola Peninsula, Russia), was determined. The mineral is monoclinic, of P21/c, a = 9.8744(4), b = 12.3981(5), c = 14.8973(7) Å, β = 104.675(5)°, V =1764.29(13)Å3, Z = 4. Yegorovite is a representative of a new structure type. Its structure is based upon the zigzag chains [Si4O8(OH)4]∞ extended along [100]. The Na atoms occupy four nonequivalent crystallographic positions and are located in six-fold polyhedra [NaO(OH)2(H2O)3] and [NaO(OH)(H2O)4]. The Na polyhedra are joined with each other by vertices and edges to form corrugated layers parallel to (001). To each of these layers, the silicon-oxygen chains adjoin from both sides, and the neighboring Na-Si layers are combined with one another by a system of H-bonds.