Induced graphitisation around crystalline inclusions in diamond

In an external vacuum and at temperatures between 900° C and 1650° C internal graphitisation takes place on or around mineral inclusions in diamond, and appears to be responsible for similar features previously reported in diamond from several localities. Several mechanisms are proposed and discussed for internal graphitisation at temperatures as low as 900° C: it is proposed that at low external pressures CO₂ exsolves from inclusions and causes internal graphitisation. The results also indicate that immediately after pressure release arising from volcanic breakthrough of kimberlites of different geological ages at several localities in West and South Africa, the temperature was not in excess of 800° C to 900° C in certain regions of the diatremes.