The linear polarization and intensity of a 22° halo has been measured simultaneously at seven wavelengths as a function of scattering angle. The polarization pattern is found to be dominated by a narrow peak centered at the halo angle. Its width indicate a effective diameter of the hexagonal face of the halo-generating crystals is found to be 41 and 54 μm for two separate scans. Halo angles could be determined with precisions better than 0.05°. An independent single-wavelength parhelion observation indicates a stronger polarization peak concentrated in an even smaller angular scattering range and a crystal diameter of 220 μm.