Chameleon Diamond Value, Price, and Jewelry Information
Professionals will tell you never to trust a trade name used to describe the appearance of a fancy colored diamond. Trade names are unofficial terms not held to a standardized ranking system. There is one exception to this rule: the chameleon diamond. The GIA has officially adopted the trade name word "chameleon" to refer to rare diamonds that temporarily alter their color (just like the reptile) in response to changes in temperature and lighting conditions. In order for the term "chameleon" to apply, the diamond must have a stable primary color that shows some green contribution and must phosphoresce under shortwave UV light. The color change from a dark greenish color to a bright orangy yellow is a truly striking effect.
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Professionals will tell you never to trust a trade name used to describe the appearance of a fancy colored diamond. Trade names are unofficial terms not held to a standardized ranking system. There is one exception to this rule: the chameleon diamond. The GIA has officially adopted the trade name word “chameleon” to refer to rare diamonds that temporarily alter their color (just like the reptile) in response to changes in temperature and lighting conditions. In order for the term “chameleon” to apply, the diamond must have a stable primary color that shows some green contribution and must phosphoresce under shortwave UV light. The color change from a dark greenish color to a bright orangy yellow is a truly striking effect.
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Chameleon Diamond Value
There isn’t much public awareness about chameleon diamonds. However, to those individuals that do know about them, a chameleon diamond can be an essential part of their personal collection. Accordingly, their price-per-carat values are high but not nearly so high as the astronomical prices that more familiar red, pink, and blue diamonds regularly fetch at auction. This makes them more attainable for those who appreciate their color-changing ability.
Like any fancy colored diamond, much of their value is linked to their carat weight. Larger stones fetch much higher per-carat values than stones weighing less than one carat. In recent years, some of the largest and most impressive chameleon diamonds have sold at auction for five figures per carat.
Chameleon Diamond Color Grading System
When gemologists grade the color of chameleon diamonds, they specifically evaluate the stable body color, not the altered hue. This means that they will examine the stone at room temperature under regular lighting conditions. A diamond must have at least some green hue in its color to be characterized as a chameleon. Chameleon diamonds may also have a mostly yellow color with only a little trace of green.
How Many Colors Can a Chameleon Diamond Show?
In general, a diamond’s color can have up to three hues, and the stable color of many chameleon diamonds has three contributing hues. When a diamond shows multiple hues, the dominant hue will be listed last and capitalized on reports. For example, a color grade of “grayish yellowish Green” means that the diamond is predominantly green with minor contributions of gray and yellow.
Like any other fancy colored diamond, graders will use the GIA’s nine-step Colored Diamond Color Grading System when examining chameleon gems. These grades, listed from most faint color expression to most powerful are: Faint, Very Light, Light, Fancy Light, Fancy, Fancy Intense, Fancy Dark, Fancy Deep, and Fancy Vivid.
Finding Chameleon Color on a Gem Report
On GIA reports, you can find the declaration that a diamond is a chameleon in the Comments section at the bottom of the page. Here, the grader will have inserted this standard sentence: “The color of this stone changes temporarily when gently heated, or when left in darkness for a period of time and is known in the trade as ‘CHAMELEON.'”
Does Chameleon Diamond Make a Good Jewelry Stone?
Fortunately, chameleon diamonds are just as durable as colorless diamonds, so you can wear them with no additional concerns. Generally speaking, gemstone durability is broken down into three categories: toughness, hardness, and stability. Diamonds are moderately tough, meaning that they can chip or fracture if hit with enough force from the right angle. When it comes to hardness, they are the single hardest naturally occurring mineral on Earth. This means that their surfaces can only be scratched by another diamond.
The stability of chameleon diamonds is a bit different. Stability refers to how a gemstone will react when exposed to certain temperatures, light, or everyday chemicals. Chameleon diamonds by nature change their appearance when heated or kept in the dark. However, these changes are temporary.
Matching Chameleon Diamonds
Finding matches for any fancy colored diamonds can be very hard due to their rarity. It takes a lot of options to find stones that share all of the Four Cs (color, cut, clarity, and carat weight). There simply aren't enough chameleon diamonds to find many matched sets. Rather, chameleon diamonds are sold individually, or the jewelry design accounts for the stones not being exactly the same.
The History of Chameleon Diamond
The recorded history of chameleon diamonds is quite sparse due to a general lack of awareness of these stones, even among members of the trade. Indeed, people may even own chameleon diamonds and remain completely unaware of their color-changing properties.
The first written record of a diamond with color-changing ability dates to 1866 and comes from a Parisian diamond merchant named Georges Halphen. However, almost eighty years passed before the term "chameleon" was first used for diamonds in 1943. Even after the diamonds were formally named, public knowledge was limited.
The GIA recounts the story of a particular buyer in the 1970s who returned a chameleon diamond because it had unexpectedly changed color in response to sitting inside the closed jewelry box. The new owner didn't recognize the stone when he brought it out.
Chameleon Diamond Color
Chameleon diamonds have two different body colors: a stable and an unstable color. The stable color of a chameleon diamond must include at least some green to be classified as such. A recent Gems & Gemology article by Breeding et al. claims that of all the chameleon diamonds examined at the GIA, 46% were grayish yellow-green. After that, 26% were a brownish greenish yellow, 16% were grayish green-yellow, and 7% were yellow-green or green-yellow. The secondary, unstable color is brighter and features yellow, orange, and/or brown hue(s).
Chameleon Diamond Color Change
Two factors will cause a chameleon gem to change from its stable color to its temporary hue: heat and a lack of light. The process involving heat is called a "thermochromic effect" while the response to darkness is called a "photochromic effect."
Thermochromic and Photochromic Effects
As a rule, the thermochromic effect occurs more rapidly than the photochromic effect. Exposure to heat completely changes the color of the diamonds in seconds. The stones will start to change color when heated to a temperature of 150° C. (To put that in perspective, a jeweler's torch can attain that easily). For the photochromic response to activate fully, the diamonds must stay in the dark for an extended period of time, on the order of multiple weeks. Once the heat is removed or the diamond is brought back into a lighted environment, the stable color usually returns in only a few minutes.
Interestingly, scientists have noticed that raw crystals of chameleon diamond often have strong color zoning. They interpret this as the diamond actually being a composite stone with multiple parts that grew under different conditions. Furthermore, analysis reveals that the individual sections house different kinds of color-causing defects.
What's the Safest Way to View Chameleon Diamond Color Change
Before we get into the mechanisms behind the color-changing effect, an important note of caution. Exposure to high temperatures may permanently erase the color of some green diamonds. This not only changes the appearance of the stone but also reduces its per-carat value significantly. As such, it is not advisable for anyone except a professional to heat a green diamond, especially if you don't know for sure that it is a chameleon.
The safest way to view diamond color change is the photochromic route. Leave the diamond in a dark place to induce the unstable color. It can take up to six weeks for the change to occur completely. You can then take the diamond into a lighted environment and watch it change from orangy yellow to darker green.
Causes of Color in Chameleon Diamonds
Chameleon diamonds are generally a subset of green diamonds, but a few are predominately yellow. Four separate mechanisms can cause green color in diamonds. For details, consult our gem listing for green diamonds. Overall, scientists have a good understanding of what causes green color in diamonds. However, some of the causes of color change in chameleon diamonds remains largely a mystery.
Here is what has been established thus far. Most chameleon diamonds are specifically Type IaA. This means there is nitrogen present in their crystal lattice, and most of those atoms sit in the carbon atomic structure in pairs. Also, chameleon diamonds have high levels of hydrogen, a very uncommon impurity rarely seen in diamonds. Thus, chameleon diamonds house both nitrogen-related defects as well as hydrogen-related defects.
Identifying Characteristics of Chameleon Diamonds
Standard Diamond Characteristics
While issues like fluorescence change with the various fancy colors that diamonds can exhibit, some measurements are universal.
- Using a standard refractometer, diamonds will register as over the limit (OTL).
- Their dispersion which causes the beautiful multicolored fiery flashes that diamonds are known for is 0.044.
- They will not show birefringence (also known as doubling) and are not pleochroic.
- Lastly, their specific gravity (SG) is 3.52 (+/- 0.10).
Since the defining feature of chameleon diamonds is their visible color change, many of the most important observations and conclusions that scientists can make come from analysis of the diamond's absorption spectrum in its stable and unstable state.
First, scientists want to understand the stable color. They note that the spectra for chameleon diamonds in their stable state has three primary characteristics that you can see using a standard spectroscope: an absorption band at 415 nm, a broad band at 480 nm, and another very broad band spanning from 700-900 nm. Observing how these bands change when the color of the diamond is altered tells us about what is happening inside the diamond that causes the phenomena.
Here is some contextual information. The ideal, pure diamond structure consists of only carbon atoms locked into a cubic formation. However, few diamonds are chemically pure. Rather, the vast majority have chemical impurities. Nitrogen is the most common. An estimated 98% of all mined diamonds have some measurable amount of nitrogen in their crystal lattice. In contrast, hydrogen is not often trapped in diamonds and is considered a rare impurity.
The Defects Associated with Chameleon Diamond Absorption Bands
Let's begin by examining what defects each band is thought to be associated with. The 415 nm band is seen in many natural diamonds and is caused by a common type of defect center, where three nitrogen atoms take the place of three carbon atoms and surround a vacant spot where a carbon atom should be. This is called an "N3 defect" and is the most well-known spectral feature of chameleon diamonds.
The second and third features are not as well understood. The 480 nm band is a characteristic coloring agent of orangy yellow diamonds. Some scientists theorize it has to do with oxygen impurities, but that has not been proven. The cause of the 700-900 nm band, most pronounced between 750-800 nm, is also not yet established but is often connected to hydrogen impurities, known characteristics of chameleon diamonds.
The presence of these three bands indicates the presence of two distinct types of defects: nitrogen and hydrogen-related defects. These distinct defect types come from different growing conditions.
For the stable color of chameleon diamonds to transmit their distinctive yellowish green color, both the 480 nm and the 750-800 nm band must be present to absorb the shortwave blue hue and longwave red hue.
How Color Change Affects the Chameleon Diamond Absorption Spectrum
For the color of a diamond to change, the transmission window created by the three defects has to be altered in response to both heat and darkness. Specifically, it has to shift away from green and towards the longer wavelengths of yellow and orange. Scientists have taken real-time UV-Vis-NIR data as they heated gems to observe the behavior of the bands.
They noted that as the temperature of chameleon diamonds is raised up to 450° C, the 480 nm band lengthens and shifts the transmission window down the spectrum to the center at 570-630 nm. The 415 nm band and the hydrogen-related band remain unchanged. This indicates an alteration in the 480 nm band causes the change in color expression.
To prove that the 480 nm band is capable of morphing in response to heat, scientists examined yellow-orange diamonds colored by the 480 nm band alone. This isolates the defect and allows for direct observation without other variables muddying the analysis. When these orangy yellow diamonds are heated, their color shifts down towards the orange range. This mirrors exactly what is observed in chameleon diamonds and proves that the 480 nm band does, in fact, react to heat by lengthening down the spectrum.
Unfortunately, this type of data collection can't measure the photochromic effect because scientists can't measure the spectra in the dark. However, the same change in the 480 nm band is presumably responsible for the photochromic response.
Answers and Mysteries
Which feature causes the color change phenomena in chameleon diamonds? The 480 nm band lengthens to move the transmission window away from green and towards yellow and orange. Nevertheless, the question remains: why exactly does the 480 nm band change? Scientists still don't know. Some have theorized that it has to do with oxygen impurities, but the exact process remains a mystery.
Fluorescence and Phosphorescence
According to Breeding et al., the first thing that you will notice if you illuminate chameleon diamonds under longwave UV light is that about 92% of all gems will fluoresce yellow, orangy yellow, or orange. There is usually also a minor yellow phosphoresce. If you use shortwave UV light, 99% of chameleon diamonds will fluoresce yellow, orangy yellow, or orange. The shortwave fluorescence isn't as noticeable as the reaction to longwave UV, but you do get strong phosphorescence that can last for up to an hour. This is considered an extreme response. The GIA requires that for a diamond to be classified as a chameleon, it must phosphoresce under shortwave UV.
Why Do Parts of a Chameleon Diamond Fluoresce in Different Colors?
Scientists can take this analysis further to learn more about what is happening internally, particularly in regard to the 480 nm and the 750-800 nm bands. The first thing that scientists notice when viewing a diamond with deep UV in a DiamondView instrument (< 230 nm) is that part of the diamond will fluoresce blue while other regions fluoresce a yellow or greenish yellow color. This pattern may manifest as large splotches but can also show intricate striping.
As the pairing of the 480 nm band and the 750-800 nm band suggests, chameleons may have grown under inconsistent conditions, resulting in certain sections having different types of defects. This is a unique characteristic of most, if not all, chameleon diamonds. Thus, scientists believe it must be some integral part of their identity.
Scientists have analyzed the greenish yellow and blue parts separately. They found the blue regions have a rise in absorption beginning at about 650 nm. They attributed this to the presence of hydrogen defects. The yellow regions do not have this feature. So, as seen with deep UV fluorescence, the blue fluorescing parts of a chameleon diamond contain hydrogen while the yellow fluorescing regions don't. Additionally, only the greenish yellow sections phosphoresce.
The clarity features of chameleon diamonds receive little notice, because their mysterious color change gets all the attention. Hydrogen-rich green diamonds can have dense, milky, cloud-like inclusions with clear boundaries. However, it is unclear if this feature is reliably present in chameleon diamonds.
Are There Synthetic Chameleon Diamonds?
Scientists can't yet grow chameleon diamonds. Such a process would be immensely complicated. It would likely involve introducing nitrogen defects in some regions and hydrogen defects in other regions.
To date, no known treatment will turn a non-phenomenal diamond into a color-change diamond.
Where are Chameleon Diamonds Found?
Though rare, green diamonds are found in many diamond mines around the world. These locations also produce the rarer chameleon diamonds.
South Africa is gaining a reputation for producing chameleon gems.
In recent years, the Marange region of Zimbabwe has become famous for yielding hydrogen-rich green diamonds. Hydrogen is a key impurity found in chameleon diamonds.
Famous Chameleon Diamonds
To date, only one notable chameleon diamond has been formally named: the Chopard chameleon diamond. Purchased by Chopard in 2007, this 31.32-ct, oval-cut diamond is the largest known chameleon diamond and is currently the centerpiece of a ring.
Chameleon Diamond Sizes
Chameleon diamonds can grow to relatively large sizes. Of the chameleon diamonds submitted to the GIA, about a third of them weighed less than half a carat. Interestingly, over half of the diamonds examined weighed between a half carat and two carats. The remaining ten percent weighed between two and four carats and higher. Some chameleon diamonds sold at auction have weighed between four and eight carats.
How to Care for Your Chameleon Diamond Jewelry
You can wear your chameleon diamond in jewelry just like any other diamond variety. Put it in a dark place for a while to enjoy the bright yellow/orange color when you bring it out. Feel free to clean at home using mild soapy water and approved diamond cleaning solutions with a soft brush. Check out our our gemstone jewelry cleaning guide for more recommendations.
Emily Frontiere is a GIA Graduate Gemologist. She is particularly experienced working with estate/antique jewelry.
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