Barium-deficient celsian, Ba1-xAl2-2xSi2+2xO8 (x=0.20 or 0.06)

Barium-deficient forms of celsian (barium aluminium silicate) with the formula Ba1-xAl2-2xSi2+2xO8 (x = 0.20 and 0.06) have been identified. In contrast with the celsian-orthoclase solid solutions which have been reported previously, these forms, refined in the space group C2/m, with Ba and one O atom in the 4i sites with m site symmetry, and a further O atom in a 4g site with twofold axial symmetry, suggest a slight solid solution with silica. The serendipitous preparation of the compounds represents a possible hazard associated with solid-state synthesis.