Crystal Structure of Yegorovite Na_4Si_4O_8(OH)_4 ? 7H_2O

摘要

Using X-ray analysis, the crystal structure of yegorovite Na_4Si_4O_8(OH)_4 ? 7H_2O, a newly-discovered mineral from the Lovozero alkaline complex (Kola Peninsula, Russia), was determined. The mineral is monoclinic, of P2_1/c, a = 9.8744(4), b = 12.3981(5), c= 14.8973(7) A, β = 104.675(5)°, V=1764.29(13)A~3, Z = 4. Yegorovite is a representative of a new structure type. Its structure is based upon the zigzag chains Si_4O_8(OH)_4_∞ extended along 100. The Na atoms occupy four nonequivalent crystallographic positions and are located in six-fold polyhedra NaO(OH)_2(H_2O)_3 and NaO(OH)(H_2O)_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.