Multimodal distribution of the geometric visible albedo of all asteroids belonging to the X complex (i.e. with spectral types found in literature being X, Xc, Xe, Xk, M, E, and P). The three peaks of the distribution correspond to the P-, M-, E-types of the Tholen & Barucci (1989) taxonomy, and their boundaries are defined p_V ≤ 0.1, 0.1 ≤ p_V ≤ 0.3, and p_V > 0.3, respectively, and are marked by the arrows at the top of the figure. As one can see these albedo boundaries provide reasonable separation between the classes. In this work we focus on X-complex asteroids with 0.1 ≤ p_V ≤ 0.3, that is, the M-types of Tholen & Barucci (1989), which in Bus-DeMeo mostly corresponds to the Xc-types.