The explanation of why diamond — the hardest material on Earth — can be polished by other pieces of diamond, and only along certain directions, has been uncovered in a paper published this week in Nature Materials. These results not only clarify this long-standing problem, but also provide an insight into similar wear processes in other materials.
Despite centuries of study, the mechanism of the polishing process in diamond has not been fully understood. In theoretical simulations, Michael Moseler and colleagues track this behaviour to a very thin layer of amorphous carbon that forms on the surface of diamond as it is polished by another diamond. They find that the formation of the amorphous film is strongly dependent on the crystallographic orientation of the diamond being polished.