Moreover, its use is preferable in the case of hybrid dense carbon allotropes, for which Lyakhov-Oganov model gives inaccurate (namely, underestimated) hardness values. Since Vickers hardness of all new carbon allotropes exceeds 80 GPa, they should be attributed to the family of ultra-hard phases . The hardness increase in the row 'glitter' -'isoglitter' -'metaglitter' is apparently due to decrease in the contribution of sp 2 hybridization and resulting density increase.