Dust absorption (Q_abs), extinction (Q_ext), and polarization (Q_pol) coefficients, as well as the polarization efficiency (Q_pol∕Q_ext), as a function of wavelength, for prolate astrosilicate grains with 20% porosity and an axis ratio ϵ = 1∕3. The radii a_V of thevolume-equivalent spheres are indicated. Black diamonds indicate the wavelength λ₀ below whichcoefficients had to be extrapolated (see Sect. 3.3).