We are currently working to determine the optical constants (n and k) of many minerals at various orientations. For uniaxial minerals, we determine n and k for the O and E rays. For other minerals, we determine the three principal complex refractive indices. We determine n and k by acquiring mid-IR emissivity or reflectance spectra and applying dispersion theory to generate optical constants that provide best-fit models to the measured spectra. Check back often to find new data. In the data files, the x axis is in wavenumber (cm^{-1}) units.