South America and Africa currently produce the majority of the world's supply of naturally coloured green diamonds. These extraordinarily rare green diamonds usually get their colour from exposure to radioactive minerals and fluids in the earth’s crust. The radiation they're exposed to knocks carbon atoms out of their normal positions, leaving empty spots in the diamond structure called vacancies. The most common vacancy defect is named “General Radiation 1” (or GR1) and it absorbs light in a way that causes diamonds to have green to blue colours, depending on the amount of other impurities present. Many green diamonds are only green on the surface and will appear near-colourless when cut. Very rarely does a natural diamond have internal green body colour like the vibrant green to greenish yellow stones seen here, making them extremely valuable. From left to right, we have: a 4.17 ct Fancy Vivid Yellowish Green diamond, a 1.53 ct Fancy Intense Green diamond set in a platinum ring, a 1.92 ct Fancy Vivid Green Yellow diamond. Learn about other types of defects that give green diamonds their colour: https://bit.ly/3ivjFWq. Photos © Optimum Diamonds.
Figure 1. Natural-color green diamonds such as these rough (0.85–1.07 ct) and faceted (0.68–1.66 ct) stones submitted to GIA by clients or for scientific study are extremely rare and generally found in South America or Africa. Photos by various GIA staff.
Among fancy-color diamonds, natural-color green stones with saturated hues are some of the rarest and most sought after. These diamonds are colored either by simple structural defects produced by radiation exposure or by more complex defects involving nitrogen, hydrogen, or nickel impurities. Most of the world’s current production of fine natural green diamonds comes from South America or Africa. Laboratory irradiation treatments have been used commercially since the late 1940s to create green color in diamond and closely mimic the effects of natural radiation exposure, causing tremendous difficulty in gemological identification. Compounding that problem is a distinct paucity of published information on these diamonds due to their rarity. Four different coloring mechanisms—absorption by GR1 defects due to radiation damage, green luminescence from H3 defects, and absorptions caused by hydrogen- and nickel-related defects—can be identified in green diamonds. Careful microscopic observation, gemological testing, and spectroscopy performed at GIA over the last decade allows an unprecedented characterization of these beautiful natural stones. By leveraging GIA’s vast database of diamond information, we have compiled data representative of tens of thousands of samples to offer a look at natural green diamonds that has never before been possible.
Fancy-color diamonds are among the most highly valued of gemstones due to their beauty and rarity. Interestingly, the rarest of diamond colors correlate with the three most popular choices for favorite color, in general—green, blue, and pink to red. The unique set of conditions in nature that produce the structural imperfections (defects in the lattice of carbon atoms; see Shigley and Breeding, 2013) responsible for the most vibrant hues of green, blue, and pink/red diamonds are so uncommon that many people are not even aware these stones exist. Over the last ten years, diamonds with these natural color components comprised less than 0.4% of all diamonds submitted to GIA’s laboratories worldwide (including both fancy-color and those on the D–Z scale). Pure hues of green, blue, or red are even rarer, accounting for less than 0.07% of all diamonds examined.
Over the last ten years, scientists at GIA have examined more than half a million natural, fancy-color diamonds and systematically documented their gemological and spectroscopic properties. Through a series of articles, we will discuss the major hue groups of natural-color diamonds in detail that has never before been revealed from such a large sampling of stones. The series will include gemological observations, spectroscopy, and statistical compilations from colored diamonds examined over the last decade at GIA.
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