Summary: Bazirite, BaZrSi₃O₉, is one o f several late-stage interstitial minerals present in the aegirine-riebeckite granite of Rockall Island. Crystals are hexagonal, probably ¯6m2, colourless, chiefly as anhedral grains. Only forms noted {10¯10} and probably {10¯14}, cleavage {0001} and probably {10¯14}. ‘Low’ and ‘high’ titanium varieties with respective mean compositions: SiO₂ 39·71%, ZrO₂ 26·38%, BaO 33·69%, TiO₂ 0·17%, SnO₂ 0·06% and SiO₂ 39·59%, ZrO₂ 26·12%, BaO 34·12%, TiO₂ 0·51%, SnO₂ 0·11%. Low and high refractive index types exist; uniaxial positive with ω = 1·6751±0·0003. ɛ = 1·6850±0·0003 and ω = 1·6813±0·0003, ɛ = 1·691 (deduced); probably due to differences in titanium content. Fluorescence (2537 Å), moderately strong, pale whitish blue. Space group almost certainly P¯6c2. Cell dimensions: low R.I. variety, a = 6·7690±0·0005 Å, c = 10·020±0·001 Å; high R.I. variety, a = 6·7662± 0·0005 Å, c = 10·158±0·0010 Å. Strongest lines are 3·80 Å (100), 2·800 (100), 5·85 (35), 3·38 (35), Z = 2. D_calc = 3·82. Related minerals, benitoite and pabstite.