Temperature-dependent transmission spectra of the forsterite crystal for orientation of the electric field parallel to the a-axis (panel a), b-axis (panel b), and c-axis (panel c). Complete temperature series (F[010]a, F[001]b, F[100]c) are plotted as solid lines, the two incomplete series as dashed lines. The F[001]a curves have been scaled by a factor of 1.8; they approximately match the F[010]a curves for the same temperatures. Dotted lines: calculated maximum transmission curves taking into account the intensity reflected by the crystal surfaces.