The crystal structure of K ₂ Si ^VI Si ₃^IV O ₉

The crystal structure of K₂Si^VI$Si3IV$O₉ has been refined in space group P6₃/m to an R = 2.02% and is confirmed to be isotypic with wadeite (K₂ZrSi₃O₉). The atomic charges of Si^VI, Si^IV, O(1 )_br and O(2)_nbr are +3.3, +2.5, −1.4 and −1.4, respectively, and suggest that an increase in the coordination number of a Si atom from 4 to 6 significantly increases the ionic character of that atom. The mean octahedral Si-0 distance, 1.778Å, compares well with that predicted by an empirical equation, 1.781 Å.