Matrix element S₂₁ of Mie-scattering matrices for Mg₂SiO₄ dust grain with optical data from Jäger et al. (2003). The top panel indicates λ = 1.2 μm, middle panel indicates λ = 1.5 μm, and bottom panel indicates λ = 2.1 μm. The dashed lines show S₂₁ for a distribution of dust grain sizes from 0.1 to 1.0 μm, and the solid lines show S₂₁ for sizes corresponding to the average size in models. Grey dotted lines show the same quantity calculated for 0.45 μm sized forsterite grains using the light scattering code MiePlot.