  Numerous experiments showed that on cold compression graphite transforms into
a new superhard and transparent allotrope. Several structures with different
topologies have been proposed for this phase. While experimental data are
consistent with these models, the only way to solve this puzzle is to find
which structure is kinetically easiest to form. Using state-of-the-art
molecular-dynamics transition path sampling simulations, we investigate kinetic
pathways of the pressure-induced transformation of graphite to various
superhard candidate structures. Unlike hitherto applied methods for elucidating
nature of superhard graphite, transition path sampling realistically models
nucleation events necessary for physically meaningful transformation kinetics.
We demonstrate that nucleation mechanism and kinetics lead to $M$-carbon as the
final product. $W$-carbon, initially competitor to $M$-carbon, is ruled out by
phase growth. Bct-C$_4$ structure is not expected to be produced by cold
compression due to less probable nucleation and higher barrier of formation.
