Blue Diamond Value, Price, and Jewelry Information

Blue Diamond Value

Natural blue diamonds are among the priciest gemstones in existence. This is due to both a very restricted supply and a consistently high demand. Even a small gem weighing a fraction of a carat will likely cost you five figures. The best blue diamonds that have sold at auction regularly fetch price-per-carat values well over one million dollars. Fortunately, scientists are now able to grow blue diamonds with relative ease, allowing per-carat prices of man-made gems to be within the reach of many more people. This means that more individuals than ever before can enjoy beautiful blue diamond jewelry.

Blue Diamond Color Grading System

Like all fancy-colored diamonds, blue diamonds are graded using the combined effect of their hue, tone, and saturation using the GIA’s 9-level Colored Diamond Color Grading System. Listed from palest to most intense, the nine grades are Faint, Very Light, Light, Fancy Light, Fancy, Fancy Intense, Fancy Dark, Fancy Deep, and Fancy Vivid. Unlike some of the other fancy colors, blue diamonds have a restricted range of saturations that they may express, and their depth of color doesn’t ever become overly deep because there is often a noticeable contribution of gray.

Does Blue Diamond Make a Good Jewelry Stone?

Like most of the other fancy-colored diamond varieties, blue diamonds are just as resilient as their colorless cousins. As the hardest naturally occurring mineral on Earth, a diamond's surface can only be marred by another diamond. Additionally, they are not affected by commonly used chemicals (such as soaps or chorine), exposure to sunlight, or normal levels of heat. Bear in mind, however, that they can chip. The delicate edges, corners, and points are most at risk. If you are going to spend the money to purchase blue diamonds, wear them with care and consider a mounting that protects the gems.

Matching Blue Diamonds

Matching diamonds means finding gems who share the same Four Cs (cut, color, clarity, and carat weight). The task of matching natural blue diamonds is a daunting prospect because there are so few of them out there. As such, you are not going to see many matched pairs or sets out there. Rather, jewelers will often embrace asymmetry and/or other fancy colored diamonds when using blue diamonds in their work so that they don't need to find matching stones.

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If, however, you are interested in synthetic blue diamond gems, it is much easier to find complementary lab-grown diamonds than the natural counterpart.

The Hope Diamond

Interestingly, one may explain the story of blue diamonds as beginning and ending with the same stone - the Hope Diamond. This speaks not only to the rarity of the blue diamonds in general, but also the social, political, and cultural importance that significant stones of any kind may come to have. Let's start at the beginning.

The Tavernier Blue

The first blue diamonds on record come from India, likely unearthed from the Kollur mine in Golconda. This should not be a surprise as India was the premier source of diamonds (colorless and fancy-colored) for the ancient world. Blue diamonds, specifically, burst onto the international scene in the 17^th century when gem merchant Jean-Baptiste Tavernier returned from India with a roughly cut 112 ct. blue diamond amongst his sparkling acquisitions. Known initially as the Tavernier Blue, the dealer sold his treasure to the King of France, Louis XIV.

The French Blue

King Louis was a larger-than-life figure who was famous for living a life of supreme luxury governed by complex rules of etiquette. He ordered the gem to be recut to an approximately 67 ct. stone and added it to the French crown jewels under a new moniker - the French Blue. Unfortunately for the members of the French monarchy, the exorbitant lifestyle that Louis demanded eventually contributed to the overthrowing of the government under the rule of his grandson Louis XVI at the end of the eighteenth century. The French Crown Jewels were looted in 1792 and the French Blue disappeared for a while. It is said that the gem was recut so that it would not be recognized.

Hope and Curse

There are theories about the next few owners of the diamond, including one about King George IV of England who may have subsequently sold it to settle debts. However, we know that Henry Philip Hope owned an exceptional blue diamond that was listed in his estate following his death in 1839. This stone is now known by his last name but the potential connection to the French Blue was not made for many decades. In addition to misfortune suffered by the previous owners, the next several owners of the Hope Diamond famously experienced some very bad luck including economic ruin and even death. This led some to wonder if the Hope Diamond bears a curse.

After passing through several more owners including the jewelry house Cartier, the gem found its current home when it was donated to the Smithsonian Institution by Henry Winston in 1958 where it has been admired at the National Museum of Natural History by over 100 million visitors. This has led some to call the Hope Diamond "the world's most famous gemstone."

Was the Hope Diamond the French Blue?

Several investigations, including one conducted by the GIA, have shown that it is possible that the Hope Diamond, which now weighs 45.52 carats, was once the French Blue. The webpage regarding the Hope Diamond posted by the Smithsonian says in no uncertain terms that their treasure is, indeed, a daughter gem of the French Blue.

Blue Diamond Color

As will be explored in detail below, most blue diamonds are colored by trace amounts of boron present in their chemical lattice. However, as boron is such a rare element, it may not be distributed in the body of the diamond evenly. Rather, it is far more likely that blue diamonds will have noticeable color zoning patterns. If you are lucky enough to examine a natural blue diamond up close, you may notice distinct borders separating strongly saturated blue areas from lesser saturated zones. Interestingly, there are rare hydrogen-rich blue diamonds that don't have boron that may also be strongly zoned.

Blue Diamond Color and Cutting

Cutters have a lot to consider when they plan how to cut blue diamonds. Firstly, they have to minimize any apparent color zoning. Additionally, blue diamond crystals tend to be asymmetric rather than having well-formed octahedral shapes. Even a fraction of a carat can mean a significant price difference, so cutters want to cut the largest possible gem from the rough. Also, many blue gems have a blended color featuring secondary hues of gray, green, or violet. Pure blue colors are much more valuable than blended colors, so cutters want to orient the stone to maximize that color.

Cutters also have to take into account whether the gem has any internal graining which will impact how they will be able to polish the gem. Finally, while large gems are more valuable than smaller ones, no one wants a big stone with large windowing or extinction patterns that distract from the beauty of the diamond.

What Causes Blue Diamond Color?

Three different sets of circumstances will cause a diamond to exhibit a blue color: boron impurities, hydrogen impurities and radiation exposure. Of these three causes, the presence of boron is by far the most common, so let's start there.

Boron

When a diamond has boron impurities but no measurable nitrogen in its crystal lattice, it is classified as a Type IIb. Type IIb diamonds are exceedingly rare, representing only about 0.1% of all diamonds, which explains why blue diamonds are so scarce. The Hope Diamond is one such Type IIb gem. There is a direct correlation between the amount of boron present and the saturation of the blue color and only a tiny concentration of the element is necessary to cause color expression. Type IIb diamond crystals may have as little as 0.01 ppm of boron, but many natural stones contain somewhere between 0.24-0.36 ppm.

As blue diamonds will usually have a gray component in their color expression, don't expect to find blue diamonds that are as deeply saturated as some other blue gemstones like sapphire. It is also interesting that, unlike other diamonds, blue boron-rich stones are excellent conductors of electricity.

Where Underground do Blue Diamonds Form?

Boron is a rare element which leads to the question of where and how blue diamonds are absorbed. There are a few clues which help researchers to answer this question. Firstly, it is known that boron is about 100 times less concentrated in Earth's mantle than it is in the crust. This suggests that the boron inside blue diamonds was, at least at one time, near Earth's surface. Secondly, while blue diamond crystals tend to be very clean, the mineral inclusions that are present are either known to be stable in the lower mantle of the Earth or are minerals which the superdeep inclusions are known to break down when the immense pressure on them lessens.

Superdeep Conditions

For example, some inclusions like walstromite (CaSiO₃) which are commonly observed in blue diamonds can only be captured in an extreme pressure environment characteristic of the lower mantle. Also, blue diamonds can have basaltic inclusions, a key component of the ocean floor. Finally, tiny ruptures in the crystal are sometimes observed adjacent to inclusions. This may be explained if the diamonds captured their inclusions in an environment of high pressure which was subsequently eased allowing them to expand a little and cause tiny cracks in the stone.

All of this information has led scientists to theorize that the gems form in a "superdeep" environment at depths of 410 miles or more as the result of plate tectonic activity. As a point of reference, this is about four times deeper than most diamond nurseries. The theory postulates that blue diamonds are made as basaltic sea floors containing boron are subducted under lighter continental masses and forced hundreds of miles down. Here, growing diamonds swallow those mineral inclusions that only exist in high-pressure environments. The same forces associated with subduction lead to volcanic activity which then brings the blue diamonds and their inclusions on the long journey back up to the surface.

Radiation

When it comes to radiation, scientists postulate that exposure inside the earth leads to a blue color that is usually modified by some green. This makes sense as a naturally occurring dominant green hue in diamonds is often caused by radiation.

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Hydrogen Impurities

Very rarely, the presence of hydrogen leads to a grayish-blue or violet color without boron or exposure to radiation. These gems are categorized as Type Ia, so they have nitrogen but lack boron, tend to be very small - usually under half a carat - and mostly came from the now-closed Argyle Mine in Kimberley, Australia. Lacking boron, hydrogen-rich blue sapphires are not electrically conductive. These stones are generally darker, exhibit more violet, and show lower color saturation than Type IIb gems. They may also be highly color-zoned.

Trade Names for Blue Diamond

You may see gems described by dealers using non-standardized terms like "ice," "navy," "royal," or "midnight." The use of these romantic terms is intended to help make a sale, rather than describe the actual color of a stone. As an overarching rule, never buy any fancy-colored diamond based on a trade name. These terms can be used by anyone any way that they like. There is no certainty - in fact it is almost impossible - that two different gems described as "navy" by different sellers will look anything alike. Always look for the standard GIA color classification terms. 

Identifying Blue Diamond

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).

Absorption Spectrum

Using a handheld spectroscope for the visible light range, Type IIb stones don't have any distinct bands, but you will see absorption increasing towards the red end of the spectrum allowing blue to be transmitted. Type Ia diamonds can have absorption bands at 545 nm and 563 nm paired with bands at 520-530 nm and 551 nm. This is combined with smaller absorption bands at 760 nm and 835 nm. A line at 595 nm suggests exposure to natural radiation or irradiation treatment.

Fluorescence and Phosphorescence

Blue diamonds don't fluoresce very often. While about 35% of colorless diamonds fluoresce what is usually a chalky blue color, very few Type IIb blue diamonds show any fluorescence at all. Those that do will glow under shortwave UV and may show blue to green fluorescence while some unusual stones glow red. It should be noted that faint blue fluorescence is sometimes difficult to identify in blue diamonds because it can be confused with the reflection of the purple UV light being used to illuminate it. If the grader has any doubts, they will assign a fluorescence grade of "none."

Diamonds in general don't phosphoresce, a phenomenon where the diamond continues to glow for a short while after UV light illuminating it has been turned off. While some rare hydrogen-rich Type Ia or the odd Type IaA/Ib chameleon gems may phosphoresce, it is usually a trait that is associated with Type IIb diamonds. The Hope Diamond, for instance, phosphoresces a red color for up to several minutes after being exposed to UV lighting.

Interestingly, spectral analysis of this phosphorescence shows that red is not the only color the Hope Diamond glows. There is also a mild green color which is masked by the stronger red. Other Type IIb gems will phosphoresce a greenish blue color only while others will phosphoresce only red or orangy red. It all depends on the exact chemistry of the individual diamond.

Hydrogen-rich blue diamonds may fluoresce a chalky yellow color which is more strongly expressed under long-wave UV light and lesser under short-wave UV light. Stones with a strong gray component also may phosphoresce a yellow color.

Clarity Features

As mentioned above, some blue diamonds have microscopic inclusions which are indicative of a super deep growing environment. Scientists use multiple investigative measures to look at these inclusions including Raman spectroscopy, mass spectroscopy, and electron microscopy.

That being said, blue diamonds tend to be quite clean, if not internally flawless. You may see some opaque black inclusions or transparent, whitish, or reflective graining. As mentioned before, one abundant mineral that is often found in blue diamonds is walstromite (CaSiO₃). Other permutations of CaSiO₃ may also be present. Scientists have observed orthopyroxene, enstatite, and olivine which can interpreted as secondary daughter minerals resulting from devolved bridgmanite, another mineral known to exist in the lower mantle.

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Are There Synthetic Blue Diamonds?

Both high pressure/high temperature (HPHT) and chemical vapor deposition (CVD) methods may be used to grow synthetic blue diamonds and these gems can be very convincing without advanced laboratory equipment to confirm their origins.

HPHT Diamonds

The HPHT process mimics the natural growing conditions for diamonds by subjecting carbon to intense heat and pressure in the presence of a seed diamond. This process can be as brief as only a few days and may be accelerated by adding boron to the chemical mix which, as you now know, results in blue stones if it is incorporated into the chemical lattice. Chemical testing shows that these gems tend to have higher concentrations of boron in their lattice than natural gems with a range of 0.82-1.12 ppm.

Magnification may reveal sharp color zoning due to inconsistent mixing of chemicals. It has also been reported that HPHT blue diamonds lack tatami strain patterns which are common in natural Type IIb stones. You may get lucky and spot tiny metallic inclusions which are indicative of the HPHT process. These diamonds may phosphoresce.

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CVD Diamonds

CVD is nothing like the natural growing process of diamonds and involves aerosolizing the necessary chemical components to encourage spontaneous diamond growth around a small seed diamond. Blue is among the possible colors that CVD diamonds may take but some say that their color may not be as saturated as HPHT diamonds.

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Sometimes, synthetic gems are subjected to secondary treatments to induce/enhance their color. For example, it has been documented that some Type IIa colorless CVD diamonds have been irradiated to take on a green blue color. 

Blue Diamond Enhancements

There are a number of things that can be done to introduce or enhance a blue color in natural diamonds. The least sophisticated method is to coat the stone in a colored wrapping. This isn't a great method because the wrappings (no matter what they are made of) will scratch, peel, and discolor over time. More permanent methods to gain a blue hue is exposure to irradiation, possibly followed by annealing which is a tightly controlled process of heating and cooling.

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Type IIb diamonds may be treated with high pressure/high temperature treatment (HPHT - not to be confused with the HPHT growth process) to remove brown and gray colors and enhance blue. This treatment is stable and can be difficult to identify without advanced testing. Sometimes you will see dark graphitization occurring around natural inclusions, but you will usually need to send the stone to a professional lab for analysis to confirm that treatment has been done.

Where are Blue Diamonds Found?

Very few mines regularly yield blue diamonds, and the historically important Kollur Mine in Golconda, India has long been inactive. Some mines in places like Borneo and South America have yielded a few surprise gems over the years, but this is exceedingly rare. The following mines have produced some impressive stones.

The Argyle Mine, Kimberley, Australia

The Argyle was perhaps the most famous diamond mine in the world thanks to the large number of fancy colored diamonds it produced. Know for pink and red diamonds, the Argyle also yielded quite a few blue diamonds, including some ultra-rare hydrogen-rich stones during its operating years (1983-2020). Some estimate that one out of 25 million carats of diamonds mined here were blue. The Argyle famously held an annual auction showcasing its best fancy colored diamonds. Its final auction in 2021 broke many pricing records.

The Cullinan Mine, South Africa

Operated by Petra Diamonds, the Cullinan has produced some truly impressive Type IIb blue stones. Analysis of the Cullinan blue diamonds indicates they grew in super-deep conditions in the Earth's lower mantle.

The Orapa Mine, Botswana

The Orapa Mine is a lucrative diamond mine in Botswana, a leading producer of natural diamonds. This large open-pit mine produces many diamonds, including some world-famous blues.

The Lesteng Mine, Lesotho

Diamonds were first discovered here in 1957, and mining began in earnest in the 1960s. Emphasizing the rarity of blue diamond discoveries, people were extremely excited when a single 12.47-ct blue diamond was unearthed in 2013.

Famous Blue Diamonds

The Wittelsbach-Graff

This 31.06 ct. diamond was most recently sold at auction in 2008 and, like the Hope Diamond, the Wittelsbach-Graff is also from Golconda, India. It is possible that it was brought to Europe by Tavernier himself. The stone has had many owners, including royalty like King Philip IV of Spain and Archduchess Maria Amelia of Bavaria. However, just as is the case for the Hope Diamond, there are gaps in the history of this stone.

In 2008, it was sold at auction to Laurence Graff who had the diamond recut to its current weight and added his name to the title. This recutting improved the color grade from Fancy Deep Grayish Blue to Fancy Deep Blue. Although some weight was sacrificed, the improved color grade is said to have increased the estimated value of the stone.

The Oppenheimer Blue Diamond

Named for its first owner Sir Philip Oppenheimer, the Oppenheimer Blue is a 14.62 ct. gem with a color grade of Fancy Vivid Blue that sold at auction in 2016 for almost 58 million dollars. Sir Philip was no casual owner as his family controlled the De Beers Group. So, if this diamond caught his eye, it certainly must be a special stone. Fashioned into an impressive emerald cut, this diamond was found in South Africa.

The Blue Moon of Josephine

Unlike the historically important gems listed above, the cushion-cut Blue Moon of Josephine was mined just a few years ago in 2014 from the South African Cullinan Mine. The rough weighed 29.6 ct. and was cut down to 12.03 ct. This stone is truly exceptional as it pairs flawless clarity with the highest color grade possible - Fancy Vivid Blue. At auction in 2014, this perfect gem sold for more than four million dollars per carat.

The Zoe Diamond

Another Fancy Vivid Blue diamond, this 9.75 ct. pear-shaped diamond sold at auction in 2014. With a clarity grade of VVS2, the Zoe appears perfectly clean to the naked eye. This gem held the record of the highest price-per-carat cost for a blue diamond until the sale of The Blue Moon of Josephine surpassed it.

The Okavango Blue

This 20.46 ct. oval blue diamond comes from the Orapa Mine in Botswana. Like the Zoe, the Okavango Blue has a clarity grade of VVS2. This diamond has yet to be sold at auction. Currently, it is owned by the Okavango Diamond Company who have lent the gem to a museum to be exhibited publicly.

Blue Diamond Sizes

While the Tavernier Blue weighed over a hundred carats, faceted blue diamonds usually don't exceed fifteen carats. Indeed, many of the significant gems sold at auction weigh under ten carats. If you conduct a search for blue diamonds on sites such as James Allen or Brian Gavin, many of the gems you will find are smaller than one carat.

How to Care for Your Blue Diamond Jewelry

Fortunately, the blue color expressed in diamonds is stable. This means that you can clean gems using all of the same methods that work for colorless diamonds. Ultrasonic machines, steamers, and gem-cleaning solutions are all safe for your special blue diamond jewelry. See our gemstone jewelry cleaning guide for more recommendations.