a cermet material and with highly reactive amorphous carbon disposed on the outer surfaces of the particulates with reference to fig1 an embodiment of a partially and discontinuously coated diamond grain 10 has a partial coat in the form of substantially discontinuous refractory microstructures 20 comprising a refractory material the refractory microstructures are in the form of u201c islands u201d or u201c patches u201d of material bonded to the surface of the diamond grain 10 the diamond grain 10 has a further coating 30 comprising a solvent catalyst metallic material the further coating being discontinuous and substantially intercalated or interspersed among the microstructures 20 of refractory material with reference to fig2 embodiments of diamond grains are coated with formations of tac and ni the diamond grains having average size of about 2 microns and the tac and ni formations having sizes of the order of nano meters the grain size of the tac is estimated to be about 40 to 60 nm in size with reference to fig3 the nickel structures of the embodiment shown in fig2 have a film or u201c halo u201d of amorphous carbon covering a surface of the nickel formations this may be as a result of nickel enhanced carbo thermal reduction of the tantalum oxide ta 2 o 5 precursor on the diamond surface to form tac carbon from the.