Gemstone Guide
Blue Diamonds
Blue diamonds are the only diamonds that conduct electricity. Their color comes from boron, an element formed in the death of stars. Natural blue diamonds sell for millions per carat. Treated and lab-grown versions put that same electric blue within reach. We sell both with every cost visible.
What Are Blue Diamonds?
Blue diamonds get their color from boron. During formation deep in the Earth's mantle, boron atoms replace carbon atoms in the crystal lattice. Those boron atoms absorb red, yellow, and green wavelengths of light and transmit blue. The result is a diamond that glows with a color no coating or treatment can perfectly replicate.
The GIA classifies natural blue diamonds as Type IIb. This designation is important because it comes with a physical property shared by no other diamond: electrical conductivity. Type IIb diamonds conduct electricity because boron is a semiconductor. You can literally test a blue diamond with an electrical probe. If it conducts, the boron is real. If it doesn't, the color came from somewhere else.
Natural blue diamonds are among the rarest gemstones on Earth. Only about one in every 10,000 diamonds has a strong natural color of any kind. Among those, blue is rarer still. The GIA grades blue diamond color intensity on a scale from Faint Blue through Fancy Vivid Blue, with each step representing a significant jump in both saturation and price.
Natural Blue: The Rarest Diamond on Earth
A natural Fancy Vivid Blue diamond can sell for $200,000 to over $3,000,000 per carat depending on size, clarity, and the purity of its blue hue. Stones with no secondary gray or green overtones are the most prized and the most scarce. Even a Fancy Blue (one grade below Vivid) regularly exceeds $50,000 per carat. Natural blue diamonds are not jewelry. They are financial instruments that happen to be beautiful.
"Only one in 10,000 diamonds possesses a strong natural color. Among those, blue is among the rarest."
— Gemological Institute of AmericaThe primary sources are South Africa's Cullinan Mine (formerly the Premier Mine, which also produced the famous Cullinan Diamond), India's Golconda region (the original source of the Hope Diamond), and Botswana. Australia's now-closed Argyle Mine produced a small number of unusual gray-blue and violet-blue diamonds colored by hydrogen rather than boron. Those stones were rare even by blue diamond standards.
Some natural blue diamonds exhibit red phosphorescence: when exposed to ultraviolet light, they glow red for several seconds after the UV source is removed. This eerie afterglow is caused by the boron in the lattice and is one of the most visually striking phenomena in all of gemology.
Famous Blue Diamonds
The Hope Diamond (45.52 Carats)
The most famous diamond of any color. Originally a 112-carat rough stone purchased by French gem merchant Jean-Baptiste Tavernier in India around 1666. It was cut into the 67-carat French Blue for King Louis XIV. Stolen during the French Revolution in 1792, it resurfaced in London decades later, recut to its current 45.52-carat cushion shape. The Hope Diamond now sits in the Smithsonian National Museum of Natural History in Washington, D.C., where it draws millions of visitors annually. Its "curse" is legendary, though largely fabricated by early 20th-century journalists.
The Oppenheimer Blue (14.62 Carats)
Sold at Christie's Geneva in May 2016 for $57.5 million, making it the most expensive jewel ever sold at auction at the time. Fancy Vivid Blue, emerald cut. Named after its previous owner, Sir Philip Oppenheimer of the De Beers diamond dynasty.
The Blue Moon of Josephine (12.03 Carats)
Sold at Sotheby's Geneva in November 2015 for $48.5 million ($4.02 million per carat). Fancy Vivid Blue, internally flawless, cushion cut. Purchased by Hong Kong billionaire Joseph Lau, who renamed it after his daughter.
The Wittelsbach-Graff (31.06 Carats)
Originally 35.56 carats with a grade of Fancy Deep Grayish Blue and VS2 clarity. Sold at Christie's in 2008 for $24.3 million. Jeweler Laurence Graff controversially had it recut to 31.06 carats, upgrading it to Fancy Deep Blue and Internally Flawless. The decision sparked fierce debate in the gem world: did Graff improve a masterpiece or diminish a piece of history? The answer depends on whether you value the stone or its story.
Treated Blue Diamonds: The Accessible Path
Natural blue diamonds are out of reach for virtually everyone. But the color itself doesn't have to be. Treated blue diamonds are natural diamonds (mined from the earth, not lab-grown) whose color has been enhanced through one of two processes:
Irradiation: The diamond is exposed to controlled radiation, which alters its atomic structure and changes the way it absorbs light. Irradiation produces blue, green-blue, and teal shades. The treatment is permanent. The diamond is safe to wear. (The Nuclear Regulatory Commission has confirmed that any residual radiation is negligible.)
HPHT (High Pressure High Temperature): The diamond is subjected to extreme heat and pressure, mimicking the conditions under which diamonds originally formed. HPHT can remove brown or gray overtones and enhance or transform color. This treatment is also permanent and stable.
Treated blue diamonds typically start as low-value colorless, brown, or lightly tinted natural diamonds. The treatment creates color that the stone didn't originally possess. The result is real diamond in every physical sense: same hardness, same crystal structure, same durability. The only difference is the origin of the color. And the price.
Treated blue diamonds over 1 carat typically come with a GIA Colored Diamond Identification and Origin Report that confirms the stone is a real diamond and discloses the treatment.
Lab-Grown Blue Diamonds: The Modern Path
Lab-grown blue diamonds are created in a laboratory using one of two methods: HPHT growth (replicating mantle conditions with a diamond seed under extreme pressure) or CVD (Chemical Vapor Deposition), which grows diamond layer by layer from a carbon-rich gas in a vacuum chamber. Blue color is achieved by introducing boron during the growth process, the same element that colors natural Type IIb diamonds.
The result is a diamond with the same chemical composition, crystal structure, hardness, and optical properties as a mined diamond. The GIA grades lab-grown blue diamonds on the same color scale (Faint through Fancy Vivid) and clearly labels them as "Laboratory-Grown" on the report.
Lab-grown blue diamonds are significantly more affordable than both natural and treated blue diamonds. They offer the most consistent color saturation because the growth process can be tightly controlled. For someone who wants the look and feel of a blue diamond without paying for geological rarity, lab-grown is the most direct path.
The trade-off: lab-grown diamonds do not hold resale value the way natural diamonds do. They are a purchase, not an investment. If that distinction matters to you, treated natural blue diamonds occupy the middle ground: real mined stones, real color enhancement, disclosed on every Manifest.
Blue Diamond Buying Guide
What Matters
Origin of color. Natural, treated, or lab-grown? This is the single biggest factor in value. The GIA report will tell you. Always ask for it. Never buy a blue diamond without documentation.
Color purity. Pure blue with no secondary gray, green, or violet is the most desirable in all three categories. "Fancy Vivid" is the highest grade. Treated diamonds can achieve vivid saturation more consistently than nature does.
Shade selection (treated). Treated blue diamonds come in distinct shade families depending on the treatment process and the starting material. Aqua, teal, ocean, sky, royal, and green-blue each have a different character.
What Doesn't Matter
Brilliance comparison to white. Blue diamonds reflect light differently than colorless diamonds. Don't evaluate them by the same sparkle standards. The color IS the feature.
Resale anxiety with lab-grown. If you're buying to wear and enjoy, not to invest, lab-grown delivers the same visual result at the lowest price point. The stone won't appreciate, but it will be beautiful every day you wear it.
Three Paths to Blue
Natural · Treated · Lab-Grown
Same color. Very different origins. Very different prices. We sell treated and lab-grown with full disclosure.
Natural Blue Diamond
$50,000 – $3,000,000+ / Carat
Type IIb. Colored by boron during formation in the Earth's mantle. Electrically conductive. Found primarily at South Africa's Cullinan Mine, India's Golconda, and Botswana. Financial instrument dressed as jewelry.
Treated Blue Diamond
Irradiated or HPHT · Natural Diamond · Enhanced Color
Real mined diamond with color enhanced through irradiation or HPHT treatment. Permanent and stable. Comes in multiple shade varieties. Over 1ct, most include a GIA report confirming real diamond and disclosing treatment.
Lab-Grown Blue Diamond
HPHT or CVD Growth · Boron-Doped
Created in a laboratory with boron introduced during growth. Same chemistry, hardness, and crystal structure as mined diamond. Most consistent color. Most affordable option. Won't appreciate in resale value.
The Treated Spectrum
Six Shades of Blue Diamond
Every treated blue diamond has a personality. The shade depends on the starting material, the treatment process, and the specific conditions applied.
Aqua Blue
Pale · Icy · Luminous
The lightest of the treated blues. A pale, crystalline aqua with a cool, icy presence. Almost transparent in feel, like frozen light. Pairs beautifully with white gold and platinum.
Sky Blue
Medium · Bright · Clean
A clear, vivid medium blue reminiscent of a cloudless winter sky. More saturated than aqua but without the green undertone of teal. The most versatile treated blue.
Teal Blue
Blue-Green · Modern · Distinctive
A blue with visible green undertones that gives it a modern, fashion-forward quality. The green secondary hue is a hallmark of irradiation treatment and is prized by buyers who want something distinctive.
Ocean Blue
Rich · Deep · Saturated
A deep, saturated blue with the richness of deep water. More intense than sky blue, less dark than royal. The sweet spot where color is undeniably strong but still shows life and movement.
Royal Blue
Deep · Commanding · Statement
The deepest pure blue in the treated spectrum. A rich, commanding color that makes a statement. Looks particularly striking set against yellow or rose gold, where the warm-cool contrast is electric.
Green-Blue
Irradiation Signature · Rare Hue
A distinctive shade where green and blue share equal presence. The natural signature of irradiation treatment. Not trying to imitate natural blue. Confidently its own color.
Blue Diamond Jewelry
Blue, Laid Bare
Every piece ships with a Transparency Manifest. Treated or lab-grown: you always know which.
Side by Side
Two Paths, One Color
Treated natural diamond vs. lab-grown. Both are beautiful. Both are blue. Both are disclosed.
Same setting. Same craftsmanship. The diamond is the variable. Treated is a real mined stone with enhanced color. Lab-grown is created in a laboratory with boron. Both confirmed by grading reports. You choose. We disclose.
The Only Diamond That Conducts
Natural blue diamonds (Type IIb) are electrically conductive because of boron in the crystal lattice. Lab-grown blue diamonds doped with boron share this property. A verifiable physical test that separates natural blue from every other diamond.
Diamond-Hard, Any Color
10 on Mohs whether natural, treated, or lab-grown. Blue diamonds have the same hardness and durability as colorless diamonds. Clean with warm soapy water. Avoid extreme heat with treated stones as a precaution.
Origin Always on the Manifest
Every TrueSanity blue diamond discloses whether the stone is treated or lab-grown, the shade variety, the grading report source (GIA or IGI), and every cost in the chain. Because "blue" alone isn't enough information.
Blue diamonds are part of the diamond family. See our April birthstone page for the full diamond guide.
Read our April Birthstone Diamond guide →Questions
Blue Diamond FAQs
Boron. During formation, boron atoms replace carbon in the crystal lattice. Boron absorbs red, yellow, and green light, transmitting blue. This also makes blue diamonds electrically conductive, a property unique to Type IIb diamonds.
Natural Fancy Blue: $50,000 to $200,000+ per carat. Natural Fancy Vivid Blue: $200,000 to over $3,000,000 per carat. The Oppenheimer Blue (14.62ct) sold for $57.5 million in 2016.
A real, mined diamond whose color has been enhanced through irradiation or HPHT treatment. The treatment is permanent and stable. The stone has the same hardness and crystal structure as any diamond. Only the origin of the color is different.
Six main shade families: Aqua Blue (pale, icy), Sky Blue (medium, bright), Teal Blue (blue-green), Ocean Blue (rich, saturated), Royal Blue (deep, commanding), and Green-Blue (irradiation signature).
A diamond created in a laboratory using HPHT or CVD methods, with boron introduced during growth to produce blue color. Same chemistry, hardness, and optical properties as mined diamond. More affordable. Will not appreciate in resale value.
Under normal wear conditions, no. Both irradiation and HPHT treatments are permanent. Extreme heat (like a jeweler's torch) could theoretically alter the color, so always inform your jeweler that the stone is treated before any repair work.
You can't with the naked eye. A GIA or IGI grading report is the only reliable way. The report will state the color origin and the diamond type. Always ask for documentation.
No. The curse narrative was largely fabricated by early 20th-century journalists. The Hope Diamond has been safely on display at the Smithsonian since 1958. It does, however, exhibit real red phosphorescence under UV light.
Yes. Same hardness as colorless diamond (10 Mohs). Treated and lab-grown blue diamonds make exceptional engagement rings with permanent, durable color.
Every blue diamond piece discloses whether the stone is treated or lab-grown, the shade variety, the grading report source, the stone cost, craftsmanship, and our protocol fee. We sell both. We label both. We price both honestly.