Black lines show the imaginary (solid) and real (dashed) parts of the complex refractive index of our newly-constructed amorphous silicate/Fe nano-particle material, a-Sil_Fe. This is a composite constructed using the amorphous forsterite-type silicate data (green) from Scott & Duley (1996) and the metallic iron data (grey) from Ordal et al. (1983, 1985, 1988), see text for details. For comparison we show the experimental data for iron-containing amorphous olivine-type silicates, MgFeSiO₄ (orange) and Mg_0.8Fe_1.2SiO₄ (brown), from Dorschner et al. (1995) and the astronomical data of Draine & Lee (1984) (cobalt blue).