Resonant Ultrasound Spectroscopy (RUS) is applied to diamonds (both cut/polished gemstones and rough diamonds) to yield a digital fingerprint from which the stone may be authenticated and sorted according to the structural quality. Diamonds are mined as rough stones from which they undergo examination to determine their value as being gem, or of two different industrial qualities. Fewer than 25% of mined diamonds are worthy of cutting and polishing to yield gems for jewelry. About 40% of the remaining population still have value as industrial diamonds for machine tools, and the rest is ground into dust to provide coatings for grinding applications. Rough stones exist in two conditions being coated and uncoated. The coated stones have a layer of polycrystalline diamond, different from the predominant crystal structure, rendering them opaque. This interferes with optical inspection, as any cracks, or inclusions can't be seen. RUS provides a reliable sorting and fingerprinting system for both cut/polished stones as well as rough diamonds of sufficient structural quality to yield a spectral signature. As high value items, diamonds are shipped around the world, and but sometimes thefts occur. RUS yields a digital fingerprint allowing the identity of an individual stone to be verified upon recovery.