Natural coloured diamond
Natural Blue Diamonds
The colour is created in the crystal lattice by trace boron — type IIb diamonds, which can even be electrically conductive. They are among the rarest natural colours of all: less than 0.02 % of all diamonds found. Every stone from 0.30 ct carries an independent GIA certificate.
Featured natural diamond
0.51 ct · · IF
Heart
DKK 506,645.00
incl. 21% VAT
From our selection
Selected natural diamonds from our offer
A live selection — each stone is unique and GIA-certified; once sold, it cannot be replaced.
The science
Why a diamond is blue: boron and type IIb
A diamond's blue colour comes from no dye or coating. It forms inside the crystal — boron atoms that replaced carbon during formation deep in the earth's mantle.
Boron in the lattice
The most common cause of natural blue is boron, which takes the place of carbon in the lattice. Boron absorbs light in the red and infrared part of the spectrum, so blue remains to the eye.
Type IIb — a rare class
Diamonds with boron belong to the rare type IIb class with very low nitrogen content. In natural blues this is extremely rare — less than 0.02 % of all diamonds found.
A diamond that conducts electricity
Unlike most diamonds, which are perfect insulators, blue type IIb diamonds are semiconductors thanks to boron and tend to be electrically conductive. Gemologists use this when verifying the origin of the colour.
GIA intensity scale
Faint → Fancy Vivid
The fancy-colour scale is entirely separate from the D–Z scale. Blue diamonds also often carry the tonal branches Fancy Deep and Fancy Dark — the Hope Diamond, for instance, is “Fancy Deep Grayish Blue”, while the Oppenheimer Blue reaches the most coveted “Fancy Vivid Blue”.
Three axes of colour
Hue, tone and saturation
Hue
The character of the colour. For blue diamonds GIA often describes modifiers — a grey or violet cast (e.g. “Grayish Blue”). A pure, unmodified blue is the rarest.
Tone
The lightness or darkness of the colour — from a soft steel blue to a deep, almost inky dark. Tone decides between the Fancy, Fancy Deep and Fancy Dark grades.
Saturation
The depth and strength of the colour. Saturation is what drives value up: a strong blue with minimal grey and a medium tone is the premium target.
„Blue is written into a diamond atom by atom. It cannot be added — only found, and exceedingly rarely.“
Arete Diamond gemological view
Honest distinction
Natural × treated × laboratory-grown colour
Swipe to see the full table
| Natural colour | Irradiation-treated colour | Laboratory-grown | |
|---|---|---|---|
| Cause of colour | Trace boron (type IIb) that replaced carbon during formation deep in the earth's mantle. | A natural diamond whose colour was altered in a laboratory by irradiation (or HPHT). The treatment is stable and legitimate, but must always be disclosed. | A stone created by the CVD or HPHT process. Physically and chemically identical to a natural diamond, but with its own GIA report (LGDR) and a more accessible price. |
| Documentation & disclosure | GIA certificate stating colour origin “Natural”. | Mandatory disclosure; GIA notes the treatment in the certificate and as a girdle inscription. Always declared. | A separate GIA report (LGDR). Always transparently labelled. |
| Value | Highest — the rarest category. | Lower than natural; valued for the accessibility of the colour. | Most accessible. |
Value & rarity
Among the rarest colours in the world
Blue makes up less than 0.02 % of all diamonds and has long been among the most sought-after hues. Type IIb stones with a pure, unmodified blue in Fancy Vivid grades are statistically almost unavailable — and that rarity is precisely what underlies their value.
< 0.02 %
Geological rarity
Blue is among the rarest natural colours — less than two hundredths of a percent of all diamonds found. Deeply blue gem-quality diamonds are exceptional.
Type IIb
Boron in the lattice
A rare group of diamonds with minimal nitrogen and a trace of boron — often semiconducting. The colour is carried by the diamond's structure, which cannot be easily reproduced.
GIA
Documented origin
For blues an independent certificate is essential. It distinguishes natural colour from irradiation-treated blue and from laboratory diamonds.
What drives the price
For white diamonds the 4Cs decide in the usual order. For coloured diamonds colour comes first — judged through hue, tone and saturation. The factors we watch:
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| Factor | What we look at | Why it matters for price |
|---|---|---|
| Intensity grade | Fancy → Fancy Vivid | The strongest price driver; Fancy Vivid with a pure blue is exceptionally rare. |
| Hue purity | Pure blue vs. grey/violet cast | An unmodified blue is rarer than Grayish or Violetish Blue. |
| Tone | Fancy, Fancy Deep, Fancy Dark | Tone decides the grade; a medium tone with strong saturation is the most sought-after. |
| Weight | Whole and threshold weights | Natural blue diamonds in larger weights are extremely rare; price per carat rises steeply. |
| Colour origin | Natural / treated / laboratory | Three separate price categories — always transparently labelled. |
Compiled by Arete Diamond gemologists for educational purposes. Not financial or investment advice.
Frequently asked
Frequently asked questions
Consultation
Looking for a particular hue or intensity grade?
We will source a natural coloured diamond to your brief — the saturation, shape and weight you want — always with a GIA certificate and documented colour origin.
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