  In the presented work, the features of mechanical stiffness of carbon
nanoparticles (nanodiamonds and fullerenes) in a wide range of sizes are
considered. The enhancement of nanodiamonds stiffness (comparing to bulk
diamond) is studied and explained in the terms of average bond stiffness $k_0$.
It is shown that $k_0$ can be useful in the description of various carbon
nanostructures and gives reliable estimates of their incompressibility.
Moreover, we found that $k_0$ can be well estimated based only on relaxed
atomic geometry.
