Table shows the crystal parameters, density and Vickers hardness obtained from the thermodynamic model. For pristine C 18 , the different values of density (ρ), hardness (H V ) and bulk modulus (B 0 ) have magnitudes close to those of diamond and lonsdaleite. This is quite expected since 9R carbon is considered to be a diamond polytype. The two hybrid allotropes show lower values closer to C 18 .