Vickers hardness (H V ) was predicted using three modern theoretical models: (i) thermodynamic model based on crystal structure and thermodynamic properties , (ii) Lyakhov-Oganov model which considers the strength of covalent bonding, degree of ionicity and topology of the crystal structure and empirical Chen-Niu model that uses the elastic properties . The fracture toughness (K Ic ) was evaluated within Mazhnik-Oganov model . Table presents Vickers hardness and bulk moduli (B 0 ) calculated in the framework of thermodynamic model of hardness; other mechanical properties such as shear modulus (G), Young's modulus (E), the Poisson's ratio () and fracture toughness (K Ic ) are given in Table . As has been shown earlier, in the case of ultrahard compounds of light elements thermodynamic model shows surprising agreement with available experimental data . Moreover, its use is preferable in the case of hybrid dense carbon allotropes, for which Lyakhov-Oganov model gives underestimated hardness values whereas the empirical Chen-Niu model does not work at all. Since Vickers hardness of both 'glitter' and 'neoglitter' exceeds 80 GPa, they should be attributed to the family of ultrahard phases . The higher hardness of 'neoglitter' is apparently due to the higher density.