Abstract
An experiment is described in which a synthetic diamond containing a high concentration of dispersed nitrogen atoms was heated at 2400 degrees C and 2500 degrees C under a stabilising pressure of about 9.5 GPa. The nitrogen atoms aggregated to form the types of nitrogen centres which are found in natural type 1a diamonds. Of particular interest was the formation of platelets in the cube planes. The results strongly suggest that the platelets were mainly composed of nitrogen atoms.