Everything to Know About Green Diamonds According to a Scientist
Dr. Evan M. Smith of the Gemological Institute of America explains how green diamonds get their color.
Gemological Institute of America
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Green diamonds are among the rarest and most valuable diamonds in the world, making up less than 0.1% of all fancy color diamonds graded by major gemological labs like the GIA.
To put that in perspective: for every 10,000 fancy color diamonds, fewer than 10 are green. And of those, truly saturated, natural Fancy Vivid Green diamonds—like the Dresden Green—are even rarer. And for every natural green diamond, there are millions of colorless diamonds in circulation. But why is something so breathtaking so hard to come by?
Normally, colored diamonds and gemstones are caused by the introduction of additional elements. For example, the substitution of boron or nitrogen atoms for carbon in the diamond crystal lattice can result in blue diamonds and yellow diamonds, respectively.
Meet the Expert
- Dr. Evan M. Smith is a Senior Research Scientist at GIA. His primary research focuses on the geology of diamonds and the inner workings of the Earth.
- He holds a Bachelor’s and Master’s degree in Geological Engineering from Queen’s University, Canada, and a Ph.D. in Geology from the University of British Columbia.
- Dr. Smith has been studying diamonds at GIA since 2015
How Does a Green Diamond Get Its Color?
However, when it comes to green diamonds, the color is often the result of something peculiar: exposure to radioactive minerals or fluids in nature, or artificial irradiation in a laboratory. Such radiation knocks carbon atoms out of place in the crystal structure, as shown below. This generates vacancies, which are essentially vacant sites where the carbon atoms are absent. The cause of color for many green diamonds is caused by the vacancy defect, also known as the GR1 center in diamond. Other defects involving nitrogen, hydrogen or nickel impurities can also cause green colors, however these are less common.
Natural Irradiation and Green Diamond Formation
Natural irradiation happens at Earth’s surface. Think of it as a sort of late stage embellishment to some lucky diamonds, which have already come a long way from their birthplace deep in the mantle. Diamonds that are eroded out of their primary volcanic host rocks and washed down rivers into secondary, alluvial deposits are much more likely to be exposed to naturally occurring radioactive materials. In this geological setting, diamonds can be deposited alongside certain crustal minerals that contain radioactive isotopes of elements such as uranium and thorium. Over thousands or even millions of years, diamonds sitting near these materials are exposed to radiation that can impart a green color.
Surface Staining: A Clue to a Green Diamond’s History
One of the most distinctive features of irradiated diamonds is the presence of conspicuous green “stains” on the rough surface, as seen on the two Brazilian diamonds below. Individual spots mark positions where radioactive mineral grains sat nestled up against the diamond, whereas more irregularly shaped stains might be caused by radioactive fluids or the presence of many fine-grained radioactive particles. This kind of staining is the result of radiation damage by alpha particles, which cannot penetrate very deep into the diamond.
Chameleon Diamonds vs. Green Diamonds
Chameleon diamonds can appear green or yellow-green under normal lighting, but they temporarily change color when exposed to heat or kept in darkness—often shifting to a brownish or orangey hue. Unlike standard green diamonds, their color change is not due to irradiation (natural or artificial) but likely linked to a complex combination of hydrogen, nitrogen, and nickel impurities, and their exact mechanism is still not fully understood.
So, while chameleon diamonds may look green at times, they are categorized separately because of their thermochromic and photochromic properties. They’re incredibly rare and highly collectible—but not considered true green diamonds
Cutting and Polishing a Green Diamond
Radiation stains usually only reach a few micrometers into the diamond and this green “skin” can be lost during cutting and polishing. Skilled cutters plan ahead in order to retain the green stains as much as possible, to control the color and overall faceted appearance. Although stains from alpha decay are relatively shallow, natural irradiation can also come from beta or gamma decay, AKA more energetic forms of radiation that can penetrate farther into the diamond to cause green body colors.
Some radiation stains appear brown, or as a mix of green and brown stains. The brown stains were initially green, but they have deteriorated with natural exposure to heat. Experiments have shown this change can occur quickly at temperatures above 500 to 600 °C, although it may occur at slightly lower temperatures in nature over thousands to millions of years.
It’s important to note that the green color’s instability at high temperatures raises concerns for polishing; manufacturers must not let the diamond become too hot during the polishing process. A conservative guideline is that if the diamond becomes too hot to touch, the color is at risk of diminishing. Below, a diamond held firmly in a device called a dop is examined carefully in the course of polishing. The finished 1.42 carat diamond is the result of slow and careful polishing without excessive heating.
Artificially Treated Green Diamonds: How They Compare
While natural irradiation can produce stunning green colors, the process can also be mimicked in a laboratory with electrons, neutrons, or gamma rays to generate vacancies and impart a green color to natural diamonds. And rest assured: the diamond does not carry any kind of residual radioactivity.
In both cases, the physical cause of color is the same, and it has been caused by the same type of process, whether it is natural or artificial irradiation. Though in some instances, a natural color origin can be concluded based on history, it’s generally difficult to determine where a diamond’s green is from. That said, the color origins ultimately impact a green diamond’s value, so advanced testing by a gemological laboratory is crucial.
The Dresden Green Diamond: A Famous Natural Green Diamond
To this day, many green diamonds in the marketplace are the product of artificial irradiation treatments, which date back to the 1940s. Logic shows that green diamonds documented prior to this time must be natural. A prime example comes from the largest and most famous green diamond, the Dresden Green Diamond, which was recovered from the historic Golconda mines of India. The Dresden Green is a 41-carat, pear-shaped stone graded as a Natural Fancy Green diamond with even color distribution—a classification that underscores its rarity.
Green diamonds are true geological marvels—extraordinarily rare, visually striking, and steeped in mystery. Whether formed through natural irradiation over millions of years or enhanced in a lab, their vivid color sets them apart from all other gemstones. As collectors and connoisseurs continue to seek these captivating stones, green diamonds remain one of the most intriguing and coveted treasures of the natural world.
