Characteristics of HPHT diamond grown at sub-lithosphere conditions (10-20Â GPa)

► Diamonds may grow in reducing or oxidising conditions at 10-20 GPa. ► Experimentally grown diamonds show extensive twinning at 10-20 GPa. ► Diamonds grown at 10-20 GPa form polygonised networks resembling carbonado. ► Experimental superdeep diamonds are octahedral at low and cubo-octahedral at high pressure.