A new Tutton’s salt Tl2[Mn(OH2)6](SO4)2 was grown from aqueous solutions and characterized by chemical analysis and X-ray powder diffraction. It was found to be monoclinic, space group P21/a, a=0.93276(6), b=1.25735(8), c=0.62407(4) nm, and β=106.310(3)°. It is unstable in warm air and dissolves incongruently. A comparison of unit cell volumes for all 37 Tutton sulfate phases found in ICDD’s PDF-2 database (86 entries) reveals a reasonable correlation with Shannon and Prewitt’s ionic radii [Acta Crystallogr. 25, 925–926 (1969)] and several deviations, most of them seeming to be erroneous entries.
