Thats right

 

Diamond is metastable state and graphite is stable form at ambient conditions

 

Diamond is thermodynamically speaking, unstable compared to Graphite and in the true sense of the word a Diamond is not forever - it will convert to Graphite over a very long, long period of time.

 

A diamond will not revert to graphite spontaneously. In order to do this, additional energy, called the energy of activation, must be added to the diamond in order to break the carbon bonds. Once this energy is added, it is possible for the diamond to change to graphite.