β-curves for amorphous carbon (‘C’, green lines, Kimura & Mann 1999), astronomical silicates (“SiO”, solid gold line, Gustafson 1994; and blue lines, Kimura & Mann 1999), and adapted astronomical silicates (“ad. SiO”) with an assumed dust density of ρ_d = 2500 kg/m³ (thick dashed maroon line; Sterken et al. 2012a). The β-curves of Kimura & Mann (1999) have porosities, p, ranging from 0% (compact particles) to 93% (fluffy particles), indicated by different line styles. (After Sterken et al. 2015, Fig. 2.)