Imaginary part of the refractive index for forsterite (upper panels) and enstatite (lower panels) in the three polarization directions: a-polarization (left), b-polarization (middle), c-polarization (right). Lower limit spectra are plotted as symbols and solid lines in colors and upper limit spectra in gray (for selected temperatures). The measured data are compared with literature data derived from reflection spectroscopy by Suto et al. (2006) for forsterite (dashed lines, 50 K and 300 K) and Zeidler et al. (2015) for enstatite (10 K and 300 K, with an extension using data from Demichelis et al. 2012, as described in the text).