A process for determining the type of a diamond having spin properties and physical properties, said process including the steps of: (i) determining the spin properties of a diamond of unknown type, using optically detected magnetic resonance to measure the spin properties of said diamond of an unknown type, wherein the spin properties are indicative of the physical properties of the diamond; (ii) comparing the spin properties of said unknown diamond with the spin properties of a plurality of diamonds of known types; and (iii) determining the type of said diamond of unknown type upon a predetermined threshold of correlation between the spin properties of said diamond of unknown type with the spin properties of a diamond of known type of said plurality of diamonds known types.