Abstract: THIS INVENTION relates to a method of or system for detecting presence of diamond in an object. The method comprises receiving classification data associated with photons emitted from object as a result of positron annihilation due to irradiation of the object with photons of a predetermined energy at which giant dipole resonance (GDR) occurs due to a nuclear reaction between the photons and carbon. The method then comprises the step of determining whether or not the object is potentially a diamond or diamondiferous by processing the received classification data with a trained machine-based learning classifier. The system typically implements the method described herein.