Refinement in space group P6 3 /m to an R = 2.02%; confirmed to be isotypic with wadeite (K 2 ZrSi 3 O 9 ). 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-O distance, 1.778 angstrom compares well with that predicted by an empirical equation, 1.781 angstrom.--Modified journal abstract.

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