Polarimetric parameter plot showing the relation between the absolute value of the minimum polarisation degree ∣P_min∣ and the inversion angle α₀. Input parameters for other low-albedo asteroids are quoted from Table 3 in Belskaya et al. (2017). The upper (∣P_min∣ = 2.0%) and lower (∣P_min∣ = 1.2%) dashed lines encase the ∣P_min∣ range of carbonaceous chondrites (Zellner et al. 1977). Thick solid curves indicate the boundaries of rocky-particulate surfaces (left curve) and particulate-fine-grained surfaces (right curve) derived from Geake & Dollfus (1986). Asterisks are the data for pulverised rocks and meteorites whose albedo is lower than 0.10 (Geake & Dollfus 1986). Parentheses in the legend show the average geometric albedo of the asteroids used here.