Gray Diamond Value, Price, and Jewelry Information

Gray Diamond Value

While there isn’t huge demand for this gem, its extreme rarity keeps per-carat prices in a moderate to high range. The value of gray gems varies widely depending mostly on color expression and carat weight. It is not uncommon to find two gems each weighing about half a carat where one is priced under a thousand dollars while the other is about ten times that amount because it has a noticeable contribution of the very valuable blue or violet hues and better clarity.

Gray Diamond Color Grading System

The grading procedure for gray diamonds is a little different from other colors and involves the implementation of both the GIA’s colorless grading scale as well as the Colored Diamond Color Grading System. Let’s first examine how each of these scales are implemented and then explore how they are used to grade gray gems.

The Colorless Diamond Grading System

The colorless grading scale, also known as the D-to-Z scale, is used to grade colorless diamonds as well as gems with light yellow, brown, or gray hues too pale to classify as fancy colors. First created in the 1950s, diamonds with a color grade of “D” are completely colorless. Each step down the alphabet represents a slightly more intense expression of yellow, brown, or gray. So, for example, a “J” diamond has less color than a “N” diamond.

The Colored Diamond Grading System

The GIA’s Colored Diamond Color Grading System is used to describe the color of yellow, brown, and gray diamonds that are darker than the D-to-Z range, as well as any other hue such as pink or green. From pale to most intense, the nine grades in this system are: Faint, Very Light, Light, Fancy Light, Fancy, Fancy Intense, Fancy Dark, Fancy Deep, and Fancy Vivid.

Are Gray Diamonds Colorless or Colored?

Which grading scale is used for gray diamonds depends on the intensity of the color expression. Diamonds that have a very pale gray hue are graded using the colorless scale exclusively through a grade of “J.” After that, things get a little more complicated. When a diamond has enough gray to rank between “K” and “M,” the official grade on the report does not use a letter. Rather, it employs one of the first three rankings of the Color Grading system. So, a gray diamond that equates to a letter “L” is graded “Faint Gray.” The next category of “Very Light” is used for gray diamonds that have enough color to be graded “N” through “Q-R.” Next, gray diamonds graded “S” through “Y-Z” are listed as “Light Gray.”

What is odd about this particular use of the ranking systems is that, even though gray diamonds with more color than a “J” grade use the first three of the Colored Diamond rankings, they are not considered fancy colored diamonds. Instead, only gray diamonds with more color than “Y-Z”/”Light” that have earned the grade of “Fancy Light” or darker are officially put into the fancy diamond color range.

Does Gray Diamond Make a Good Jewelry Stone?

Gray diamonds can be used in jewelry just as colorless diamonds are! They have the same durability scores so they can be worn without any additional precautions or concerns. Despite having multiple coloration mechanisms, the gray color of diamonds is stable. Normal exposure to light, heat, and everyday household chemicals won't harm them. 

Unlike many other fancy colored diamonds, gray diamonds are often cut in a round brilliant shape. Since the round brilliant cut is meant to enhance colorlessness, cutters usually don't use it for colored diamonds. For these stones, hue is the most valuable factor. However, gray tones of many different intensities all have their own following. Accordingly, cutters often choose to facet gray diamonds into round shapes. As round brilliant cuts are the most popular cut for engagement rings, this is an important selling point.

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Matching Gray Diamonds

Matching gray diamonds is a challenge for artists and designers because there are so few stones out there. Furthermore, they can show a wide range of colors, from pure gray to blue, purple, violet, yellow, and green tones. As with most fancy colored diamonds, you're more likely to see jewelry highlighting a single gray stone or designs featuring purposefully mismatched stones.

The History of Gray Diamond

Pure gray diamonds are among the least appreciated of all the fancy diamond colors. As such, there isn't really a known history specifically about them. Before gray diamonds gained any following, they were often seen as dirty colorless diamonds without much value. Compounding the issue is that large gray diamonds are exceptionally rare. Most gray rough crystals weigh under four carats, an unimpressive number in the world of colorless diamonds. As such, there was little demand for them in the jewelry market.

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On the other hand, gray diamonds' more valuable blue and violet cousins with gray modifiers have more documented history. For example, the most famous diamond in the world, the Hope Diamond, is a blue gem modified by gray.

Gray Diamond Color

The causes of gray color in diamonds are similar to those of blue and violet. Thus, gray, blue, and violet diamonds are often grouped together. These stones will often show two of these hues at the same time. In 2018, Gems & Gemology published an article by Sally Eaton-Magaña, Christopher M. Breeding, and James E. Shigley that reported their findings about such diamonds examined by the GIA over the past decade. Of this color group, they reported that about a third were pure gray, 16% were gray/blue, and approximately 4% were gray/violet. Gray can also appear in combination with purple, green, chameleon, and yellow hues.

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What Causes Gray Diamond Color?

According to Eaton-Magaña et al. three primary mechanisms cause a strong gray color in diamonds: boron impurities, hydrogen impurities, and clouds of micro-inclusions. A rare fourth type of diamond owes its gray color to radiation damage. To grasp how each of these four mechanisms operates, one must understand the structure of an idealized, unaltered diamond crystal.

Diamond Crystal Structure

Fortunately, the pure diamond crystal is easy to understand. It consists of carbon atoms only, interlocked with each other in a highly symmetrical pattern. This is a response to extreme temperatures and pressure conditions that exist inside the Earth's mantle. Since the atomic structure is so regular, light passes through without hindrance. This results in a colorless stone that doesn't exhibit any hue in any direction. 

However, nature rarely gives us a pure crystal. Rather, four factors can cause gray color in diamonds:

• The absorption of chemical impurities during its growing phase
• Structural defects inflicted on a mature crystal by prolonged exposure to high levels of heat and pressure
• The presence of many darkly-colored inclusions
• Damage caused by exposure to radiation.

Boron Impurities

The presence of rare boron impurities sometimes paired with plastic deformation can lead to a gray color paired with blue. This is a combination of the first two color triggers acting at the same time. Boron atoms take the place of carbon atoms in the crystal structure in a simple case of substitution. Generally, gems with high concentrations of boron show a more pure blue expression, while lower amounts express more gray. Boron impurities are famously the coloration mechanism behind the Hope Diamond. 

The plastic deformation sometimes paired with boron impurities magnifies the gray color component. This happens after the crystal has grown and is characterized by atomic irregularities caused by extreme heat and pressure. Let's look at that more closely.

The carbon atomic structure of a diamond is very regular and very strong. It is why diamonds are the hardest mineral on Earth. However, if you spin the crystal and peer through the atoms, you will notice that there is a particular direction known as the octahedral plane where there is a relatively wide gap extending through the gem. This gap is a plane of vulnerability. When mature diamonds are exposed to intense heat and pressure, their atomic structure can shift here. The gem does not break. However, more accurately, it slides a bit. This is plastic deformation, and it creates what gemologists call "glide planes" or "graining patterns." Because the atoms are no longer aligned, graining patterns create and concentrate color within themselves. Graining can cause pink and brown hues as well as gray.

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Hydrogen Impurities

Another color trigger is the presence of hydrogen impurities. Although less understood than the boron/plastic deformation mechanism, a high concentration of hydrogen is known to lead to pronounced gray color. For decades, scientists have known that diamonds can host hydrogen impurities but still don't know exactly how they create color. Gray/blue/violet diamonds can have hydrogen impurities, as can some green gems. It has been established that hydrogen-rich diamonds can host complicated N3 defects which are centers where three nitrogen atoms (the most common chemical impurity in diamonds) cluster around a vacancy where a carbon atom should be with a single hydrogen atom being present. Research into this topic continues.

Micro-Inclusions

Some gray diamonds are not colored on the atomic level but only appear to have a gray color because there are many tiny inclusions scattered throughout the body of the crystal. Of the gray/blue/violet diamond group, this coloration mechanism is exclusive to gray gems. Interestingly, Eaton-Magaña et al. state that most of the diamonds colored by cloud-like inclusions are specifically some form of Type Ia diamonds. This means that the diamonds have nitrogen impurities. The nitrogen atoms may be aggregated in pairs (Type IaA), grouped in clusters of four surrounding a vacancy where a carbon atom should be (Type IaB), or may show both types of centers simultaneously (Type IaAB). Furthermore, they say that some of these gray diamonds have so much nitrogen that their distribution in the atomic lattice can't be determined.

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What are the Cloud-Like Inclusions?

What the cloud structures actually are remains a mystery. Some data suggests they are areas of especially high hydrogen concentration. However, Eaton-Magaña et al. stress that these clouds are distinct features from the hydrogen atom impurities discussed above.

Graphite Inclusions

Alternatively, Eaton-Magaña et al. say that it is more likely that the coloration is caused by color zoning patterns whereby gray diamonds grow in a "mixed habit" with both the regular octahedral regions as well as areas of unusual cuboid growth. They explain that the cuboid sectors have many inclusions of dark graphite, a soft form of carbon that failed to convert to diamond during formation. These individual graphite inclusions are often no larger than 1µm but can grow to as large as 4 µm if the diamond is heated to 1200° C. So, such diamonds may be colored by a mixture of both the original 1µm inclusions as well as larger inclusions.

Other Materials

It is noted that these dark inclusions may not be exclusively graphite and might contain other dark materials. Some theorize these types of gray diamonds absorbed so many impurities and inclusions partly due to a rapid growth rate. These diamonds often have low clarity grades with many eye-visible inclusions.

Radiation Damage

A very small percentage of blue-gray and gray-blue diamonds are colored by radiation damage. When a diamond is exposed to radiation while still deep within the Earth, the radioactive isotopes can push individual carbon atoms out of place. This leaves a vacancy in the crystal lattice. The displaced carbon atom, now called an "interstitial," gets stuck between neighboring carbon atoms. These individual damage locations are called GR1 defects. Most often, GR1 defects create a green color, but a few rare blended blue/gray diamonds are colored by this mechanism.

Gray Diamond Trade Names

Trade names are unofficial terms used by some sellers to help market their inventory. It is important to understand that these are descriptive terms that are not held to any regulated standard. Dealers often use them to add romantic associations to their diamonds. Of course, they hope this will help sales. Some trade names you might encounter are "silvermist," "raw," "rustic," "shale," and "steel."

Are "Salt and Pepper" Diamonds a Type of Gray Diamond?

You might find the term "salt and pepper" used to describe gray diamonds. However, take a close look at those diamonds. Usually, the term "salt and pepper" describes colorless diamonds with many eye-visible black inclusions, not gray diamonds. 

Never trust a trade name when shopping for a fancy colored diamond. Instead, look for the GIA color grade and, if possible, take a firsthand look at the gem under good lighting conditions.

Identifying Gray Diamond

Standard Diamond Characteristics

While issues like fluorescence change with the various fancy colors that diamonds can exhibit, some diamond 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).

Absorption Spectrum

The absorption spectrum of diamonds determines which light wavelengths are transmitted, and a number of different absorption patterns lead to a gray color. It all depends on the type of mechanism that colors a particular gem. Eaton-Magaña et al. look at the spectral features for each different cause. Here are their findings.

Absorption Spectrum for Gray Diamonds with Boron Impurities

There are no bands related to boron impurities. Rather, you will notice a general absorption that increased towards the red end of the spectrum. If the gray color of a gem is magnified by plastic deformation structures, this will further absorb light with wavelengths less than 500 nm.

Absorption Spectrum for Gray Diamonds with Hydrogen Impurities

In diamonds with hydrogen impurities, Eaton-Magaña et al. describe how two broad absorption bands allow the transmission of both blue and red colors. Specifically, there are strong peaks centered at about 530 nm and 720 nm, but the exact location varies between stones. Also, the spectra have the characteristic 835 nm band known as the "hydrogen band" and sometimes have a narrow band at 551 nm, the causes of which are not yet understood. It is theorized that there are as-yet-undiscovered defects behind these features.

Absorption Spectrum for Gray Diamonds with Inclusion Clouds

Like the gray diamonds colored by boron, gems that appear gray due to clouds of dark inclusions don't have any distinctive absorption patterns beyond gradual absorption of longer wavelengths.

Absorption Spectrum for Gray Diamonds with Radiation Damage

Ordinarily, GR1 defects pull out red and blue light to create green gems. Very rarely, this transmission window will lead to blue/gray colors.

Absorption Spectrum Anomalies

Scientists have studied a few gray diamonds colored by a 480 nm band, a feature observed in chameleon diamonds. The defect behind the 480 nm band has yet to be identified. However, because it is so closely linked to chameleon diamonds, it is thought that such gray gems are actually chameleon diamonds that have such a low color saturation that only gray is observable.

Fluorescence

As with the absorption spectra data, the different types of gray diamonds fluorescence differently. Gems with boron very often phosphoresce a red color, a rare reaction for diamonds. Hydrogen-rich gray diamonds often fluoresce a yellow color.

Eaton-Magaña et al. report that 61% of gray diamonds fluoresced under longwave UV light while 90% responded to shortwave UV light. Grays that have the 480 nm band also fluoresce yellow. They do not discuss any specific responses to gray gems colored by inclusions or GR1 defects.

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Clarity Features

Since four independent conditions can make diamonds gray, gray diamonds can have different types of inclusions depending on the source of their color. 

Diamonds colored by boron impurities with plastic deformation are thought to have formed in super deep environments, as dense basaltic sea floors subduct underneath lighter continental plates. Although usually clean, these gray diamonds can house unusual inclusions of minerals found in the lower mantle, like walstromite (CaSiO₃) and some of its permutations. These gray diamonds may also have basaltic inclusions. 

The gray diamonds characterized by atomic hydrogen impurities and those with larger dark inclusions are both thought to have grown at a rapid pace. This allowed them to absorb more impurities present in their growth environment than they would have had they grown at a slower pace. The hydrogen-rich diamonds pulled in more hydrogen atoms, while the diamonds colored by inclusions swallowed more minerals and fluids. 

Gray diamonds colored by GR1 defects do not have any distinctive clarity features.

Are There Synthetic Gray Diamonds?

Laboratories have used both chemical vapor deposition (CVD) and high pressure/high temperature (HPHT) processes to create gray diamonds. The GIA has noted that HPHT usually produces darker gray gems, often with some red, while CVD produces paler gray diamonds. Some HPHT gray gems are subjected to post-growth treatments to further enhance their color. 

Interestingly, Eaton-Magaña et al. report that some low-quality CVD synthetic diamonds have graphitic inclusions that strongly resemble those of their natural gray counterparts.

Gray Diamond Enhancements

In diamonds, gray often occurs in concert with other hues. Some of these hues, like blue and violet, add far more value with less gray showing. As a result, many mixed-hue diamonds receive treatments to remove as much gray as possible.

Blueish gray diamonds colored by boron will be subject to high pressure/high temperature treatment to decrease the gray and enhance the blue.

Gray diamonds colored by graphite inclusions can be heated to increase the size of those inclusions and darken the stone's color overall. This can darken the gray color or even cause the gem to become black.

Where are Gray Diamonds Found?

Gray diamonds are found in multiple locations around the world.

Africa is a leading diamond producer. The famous Cullinan Mine in South Africa, known for producing some of the world's largest colorless diamonds, also yields gray stones colored by boron impurities with low, if not imperceptible, levels of nitrogen.

The recently closed Argyle Mine in Northwestern Australia regularly produced gray gems that contained high concentrations of hydrogen impurities.

Mines in other locations like Brazil, India, and Russia also occasionally produce gray diamonds.

Famous Gray Diamonds

Diamonds with a dominant gray color have a low public profile and tend to weigh less than four carats. As a result, there are no significant named gray diamonds. However, there are famous blue diamonds modified by some gray, such as the Hope Diamond, graded a Fancy Dark grayish Blue.

That being said, some truly exceptional gray diamonds are available. At the end of 2022, a beautiful 10.67-ct Fancy Gray set in a modern ring mounting sold at auction for 1.1 million dollars. 

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Gray Diamond Sizes

Like many fancy colored diamonds, gray diamonds tend to form as small rough crystals. Of the 15,000 blue/gray/violet diamonds submitted to the GIA and examined by Eaton-Magaña et al., 63% weighed less than one carat. When conducting an online search, you may find gray diamonds weighing up to about two and a half carats. However, finding anything larger might be a challenge. You will also find high per-carat price increases.

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How to Care for Your Gray Diamond Jewelry

Fortunately, most gray diamonds have the same durability as colorless diamonds. You can care for them using the same techniques and cleaning solutions. However, any gray diamonds colored by many large inclusions may have compromised stability. Avoid putting these stones in an ultrasonic or steam cleaning machine. Instead, use mild soapy water or diamond cleaning solution and a soft brush. Check out our gemstone jewelry cleaning guide for more recommendations.