Transformation of diamond to graphite

Despite almost forty years of trying, no one has managed to transform diamond into graphite under pressure1, or find out what the pressure limit for diamond might be2. If diamond were to behave like other group IV elements, such as silicon, germanium or tin, it would transform under compressive indentation to the β-tin structure3, but it does not2,4. Here we use micro-Raman spectroscopy to determine what happens to diamond when it is subjected to high contact compression as a result of pressing a sharp diamond indenter against its surface4. We find that, under this non-hydrostatic compression, diamond at the point of indentation is transformed into disordered graphite. This discovery may eventually lead to the more efficient machining of diamond.