Diamonds come in a variety of colors, including clear, yellow, brown, pink, blue, green, and more. The rarest and most valuable diamond color is an intense blue. Only a very small percentage of diamonds mined have any blue coloration at all, and the more saturated the blue, the rarer the diamond. So what causes some diamonds to have a blue tint? There are a few key factors that contribute to a diamond’s blue color.
Chemical Composition
The blue color in diamonds is caused by the presence of the chemical element boron during crystal formation. Diamond crystallization occurs deep underground under intense heat and pressure conditions. If there are trace amounts of boron present in the environment during crystallization, the boron atoms can get incorporated into the diamond’s crystalline structure.
Boron is an element with one less electron than carbon in its outer shell. When boron replaces a carbon atom in the diamond lattice, it causes gaps or holes where electrons are missing. These gaps allow the diamond to absorb light in the red end of the visible spectrum, while reflecting back blue light. The more boron present, the more intense blue coloration.
Type IIb Diamonds
Diamonds are categorized into types based on their level of impurities. Type II diamonds have very low levels of nitrogen impurities, but may contain boron. Type IIb diamonds have no measurable nitrogen impurities and contain significant levels of boron—these are the diamonds that can display a blue hue. The combination of no nitrogen impurities and the presence of boron makes it possible for type IIb diamonds to transmit blue light.
Natural Blue Diamonds
Natural blue diamonds occur when there are accidental trace amounts of boron present as the diamond forms in the earth’s crust. The conditions need to be just right for boron to be available but nitrogen absent in order for blue diamonds to form naturally. This is an extremely rare occurrence, even more so than for other fancy colored diamonds like pink or yellow.
Some famous natural blue diamonds include:
Hope Diamond
The Hope Diamond is a 45.52 carat intense blue diamond discovered in India in the 17th century. It has an estimated value of $200-250 million USD.
Wittelsbach-Graff Diamond
This 31.06 carat diamond sold for $24.3 million USD in 2008. It originates from the famous Wittelsbach diamond mined in India in the 17th century.
Heart of Eternity
A 27.64 carat blue diamond found in South Africa at the Premier Mine in 2000. It is considered one of the most valuable blue diamonds in the world.
Color Grading Scales
Gemological laboratories like GIA use color grading scales to assign grades to fancy color diamonds like blue diamonds:
For Natural Blue Diamonds
| Grade | Color Description |
| Fancy Light | Very light blue |
| Fancy | Light to medium blue |
| Fancy Intense | Medium to strong blue |
| Fancy Vivid | Strong to vivid blue |
| Fancy Deep | Vivid to deep blue |
| Fancy Dark | Deep blue |
For Treated Blue Diamonds
| Grade | Color Description |
| Fancy | Light to medium blue |
| Fancy Intense | Medium to strong blue |
| Fancy Vivid | Strong to vivid blue |
The stronger the saturation, the higher the grade and value. Completely colorless diamonds are graded D-F on a separate white diamond color scale.
Blue Diamond Treatment
Natural blue diamonds are so incredibly rare that the majority of blue diamonds on the market have been artificially treated to change color. Common treatments include:
HPHT Treatment
Using high pressure, high temperature conditions, natural brown type IIa diamonds can be altered into blue diamonds. The intense heat and pressure drives boron atoms deeper into the diamond structure, altering light transmission.
Irradiation
Diamonds are exposed to radiation treatments like gamma rays, neutrons, or electrons. This radiation causes structural changes that induce blue coloration. Almost all irradiated blue diamonds have a greenish hue under the face up crown.
Coating
A thin translucent film can be applied to the surface of the diamond to produce a blue appearance. Coatings can fade or scratch off over time if not properly maintained.
Treated blue diamonds tend to have an unnatural appearance under close inspection compared to untreated natural blue diamonds. GIA labs can detect most common treatments. Whether treated or not, blue is one of the rarest diamond colors, commanding high values.
Where Blue Diamonds Are Found
Most natural blue diamonds originate from a few select sources. The Golconda region of India was an early source for historic blues like the Hope Diamond. In more modern times, blue diamonds have been mined primarily at the Cullinan mine in South Africa and the Argyle mine in Australia:
Cullinan Mine
Part of the Premier Diamond Mine in South Africa. Blue diamonds were first discovered here in 2009. It has produced blues like the Blue Moon of Josephine (12 carats), and a 24.18 carat blue that sold for $46.2 million.
Argyle Mine
An Australian mine known for pink and red diamonds, but has also produced rare blues. Home to the Argyle Violet, a 2.83 violet-blue considered the largest found. The mine is now depleted and closed as of 2020.
A small number of blue diamonds have originated from other mines in South Africa, Russia, and Canada, but Cullinan and Argyle were the primary modern commercial sources.
How Much Do Blue Diamonds Cost?
Blue diamonds are exceptionally rare, currently make up less than 1% of colored diamond production. Increased demand from investors and collectors make blue diamonds highly coveted. Blue diamond prices per carat increase exponentially based on the intensity of color, from thousands to millions of dollars per carat for vivid blues.
| Blue Diamond | Carat Size | Price |
| De Beers Centenary | 5.99 | $48 million |
| Blue Moon of Josephine | 12.03 | $48.4 million |
| Oppenheimer Blue | 14.62 | $57.5 million |
| Pink Star | 59.60 | $71.2 million |
In general, prices per carat can range from:
– Fancy Light Blue: $5,000 to $15,000 per carat
– Fancy Blue: $15,000 to $25,000 per carat
– Fancy Intense Blue: $25,000 to $50,000 per carat
– Fancy Vivid Blue: $50,000 to $500,000+ per carat
But large vivid blues over 5 carats can easily fetch multimillion dollar prices at auction. The rarity and mystique of blue diamonds make them an intriguing choice for diamond collectors and investors.
Blue Diamond Jewelry
Given their extremely high value, most blue diamonds are sold loose or made into exclusive jewelry pieces by high-end designers:
Engagement Rings
Blue diamonds can make for unique, non-traditional engagement rings. Celebrities like Penelope Cruz and Salma Hayek have received blue diamond rings.
Necklaces
Important blue diamonds are often the showstopping centerpieces of necklaces, like the famous Hope Diamond jewelry suites.
Earrings
Match pairs of blue diamonds can be made into stunning earrings. Many natural blue diamonds are under 1 carat, well-suited for earring designs.
Bracelets
Bracelets allow for a line of blue diamonds to be worn in a flexible piece. Tennis bracelets set with blue diamonds are especially dazzling.
Brooches
Historical and vintage blue diamond jewelry often included brooches, which accentuate the gemstone(s) in a wearable fashion.
How to Buy a Blue Diamond
For buyers looking to invest in a blue diamond, either as jewelry or a collector’s item, here are some tips:
– Get a grading report from a respected lab like GIA or AGS to authenticate the diamond and color grade.
– Buy from a reputable dealer with expertise in rare colored diamonds.
– Carefully inspect the diamond yourself or have it evaluated by an independent appraiser.
– Confirm the diamond is untreated unless you are interested in treated blues.
– Compare prices based on the 4C’s – carat, cut, color and clarity.
– Consider the setting style that will best showcase the diamond.
– Calculate the resale value and potential appreciation over time.
– Ensure your jeweler provides documentation of authenticity and provenance.
Investing in a blue diamond requires significant research and care. But for the right buyer, they offer an exceptional combination of beauty, rarity and investment value.
Conclusion
Blue diamonds derive their captivating color from the presence of the element boron during their formation in the earth’s crust. Only a handful of diamond mines have produced rare natural blues, prized for their intense saturation. While most blue diamonds are treated, natural untreated blues are the most valuable and coveted. The intensity of blue color has a huge impact on price, with vivid blues selling for millions per carat. For diamond lovers, a blue diamond is the ultimate treasure.