IDENTIFICATION OF GREEN COLORED GEM DIAMONDS: AN ON-GOING CHALLENGE

Naturally occurring green color in gem diamond is highly valued due to its rarity. Green color can be produced by several defect mechanisms, but the most common results from exposure to radiation. Even when enough natural radiation damage is present to produce green color in a diamond, it is usually restricted to the very shallow rough surface of the stone and is often removed during faceting. Because of the appeal of green diamonds, artificial irradiation treatments have been performed on gem diamonds since the early 1900s. What began with radium salts is now routinely done using electrons, neutrons, or gamma rays. Unlike with many other diamond treatment processes, laboratory irradiation causes changes in the atomic lattice of diamond that are virtually identical to those produced in nature. For decades, this has proven to be the bane of gemologists who try to determine the origin of color in green diamonds, often leading to “Undetermined” reports from gem labs. Combinations of gemological observations with UV-visible-NIR and infrared absorption spectroscopy provide some help with separation. Comprehensive irradiation experiments and characterization of known natural green diamonds are the keys to developing better criteria for separation of naturally colored from artificially irradiated green diamonds.