Effect of fO₂ on the spectrum of a mineral atmosphere at constant melt composition (TERRA) and irradiation temperature (2500 K) for an Earth-sized planet. Shown are the stellar spectrum (top), the spectrum of planetary emission (center, coloured) and the secondary occultation depth F_p/F_*, the ratio between the two (bottom, colours). The emission from metallic species (Fe, Mg, MgO, TiO) in the visible distorts the overall shape of the spectral energy distribution (SED) compared to a pure black body. This effect is pronounced in reducing atmospheres, whereas oxidised ones follow a black body more closely except for a handful of strong lines.