The crystal structures of two manganoan 1M-phlogopites and kinoshitalite-1M (Ba, Mn brittle mica) have been re-examined to determine if cation ordering patterns in subgroup symmetries exist. In all cases, the X-ray single crystal data are better explained by the ideal symmetry of C2⁄m, which requires only one tetrahedral site (and no tetrahedral Si–Al order) and only two independent octahedral sites. Since tetrahedral Si–Al order is known for all other brittle micas with Si to Al ratios near 1:1, the kinoshitalite sample of this study, which is from a contact metamorphosed manganese deposit, may have formed under conditions that fail to promote tetrahedral order. However, undetected twinning of the kinoshitalite crystal, which could affect these results, cannot be ruled out.