Secret of ultra-hard graphite unlocked: "Graphite squeezed between two diamond jaws at pressures of 170,000 atmospheres managed to produce a crack in the diamond. The atomic structure of the material remained elusive, however.
Now computer simulations by Hui-Tian Wang at Nankai University in Tianjin, China, and colleagues have shown that the compressed material could be at least partly made of bct-carbon, which is built up from rings of four carbon atoms. Bct-carbon has attributes of both diamond, which has a cubic structure, and graphite, composed of loosely linked sheets of carbon atoms in a hexagonal lattice. In bct-carbon, layers of carbon rings are linked by strong vertical bonds."