Diamonds have fascinated people for centuries with their dazzling brilliance and enduring hardness. There are many factors that contribute to a diamond’s quality and value, including the 4Cs – Cut, Color, Clarity, and Carat weight. However, one of the most basic distinctions between diamonds is their type. Diamonds are categorized into 5 main types based on their chemical composition and how they were formed. The 5 major types of diamonds are:
Type I Diamonds
Type I diamonds are the most common, accounting for around 98% of natural diamonds. This category includes diamonds that have detectable levels of nitrogen impurities, which can influence their optical properties. Type I diamonds are further divided into 2 sub-categories:
Type Ia – Most contain detectable nitrogen impurities
Over 95% of Type I diamonds fall under the Type Ia subgroup. These diamonds contain up to 0.1% nitrogen impurities, which are evenly distributed throughout the crystal structure. The nitrogen atoms give these diamonds a slight yellowish tint.
Type Ib – Contain significant nitrogen impurities
Type Ib diamonds make up less than 0.1% of natural diamonds. They contain significant levels of nitrogen impurities, from 0.1% to 1% nitrogen content. The high nitrogen concentration gives these diamonds a distinct yellow or brownish color. The most famous Type Ib diamond is the Hope Diamond.
Type II Diamonds
Type II diamonds contain no measurable nitrogen impurities. They make up around 2% of natural diamonds. Type II diamonds are also divided into 2 sub-categories:
Type IIa – Chemically pure with no impurities
Type IIa diamonds are the chemically purest form of natural diamonds, containing no measurable nitrogen or boron impurities. They have excellent transparency and make up around 1-2% of natural diamonds.
Type IIb – Contain measurable boron impurities
Extremely rare, Type IIb diamonds contain detectable levels of boron impurities, from 0.1% to 0.5% boron content. Boron gives these diamonds a blue hue. Type IIb diamonds make up less than 0.1% of diamonds mined. The famous Hope Diamond is classified as both Type Ib and Type IIb.
| Diamond Type | Nitrogen Content | Color | Rarity |
|---|---|---|---|
| Type Ia | Up to 0.1% | Slight yellowish tint | Common (~95% of diamonds) |
| Type Ib | 0.1% to 1% | Yellow to brown | Very rare ( |
| Type IIa | None detected | Colorless | Rare (1-2%) |
| Type IIb | 0.1% to 0.5% boron | Blue hue | Extremely rare ( |
The table summarizes the key distinguishing features between the 4 main sub-categories of diamonds. Type Ia diamonds are by far the most common, while Type Ib and Type IIb diamonds are exceptionally rare.
How Diamonds Form by Type
The different diamond types form under varying conditions of temperature, pressure, and chemical environment deep underground. Here is a look at how each diamond type is created in nature:
Type I Diamonds
Type I diamonds originate from deposits that are rich in nitrogen. During diamond formation, nitrogen atoms get incorporated into the crystal lattice. The amount of nitrogen present determines if a diamond is Type Ia or Type Ib.
Type IIa Diamonds
Type IIa diamonds form from very pure sources that contain little to no nitrogen or boron impurities. The extreme heat and pressure crystallize carbon into diamonds free of these impurities. Type IIa diamonds originate from ancient geological formations that predate the existence of nitrogen and boron.
Type IIb Diamonds
Type IIb diamonds are born from sources that contain boron. While boron is rare in Earth’s crust, the deep mantle has higher concentrations. As Type IIb diamonds form, available boron gets built into the crystalline matrix, giving the diamonds a blue coloration.
Evaluating Diamond Quality by Type
When assessing diamond quality, the diamond type can offer useful insights but doesn’t necessarily indicate one type is better than another. Here are some factors relating diamond type to quality:
Color
Type IIa diamonds are considered the most colorless, while Type I and IIb diamonds have variable color saturation from the impurities. A D-color Type IIa diamond would be considered superior for colorlessness to an equivalent D-color Type Ia diamond.
Clarity
Type IIa diamonds often have exceptional clarity since they formed without nitrogen impurities. Type Ib diamonds tend to have more inclusions from their high nitrogen content. However, clarity depends more on an individual diamond’s characteristics than its type.
Cut
No one diamond type has superior cutting characteristics. The quality of the cut determines how well a diamond reflects and refracts light. Cut quality ranges equally across all diamond types.
Carat
Large diamonds over 1 carat are rare and valuable in all diamond types. Type IIa diamonds over 5 carats are exceptionally rare and command record prices when they come to market due to their combination of size and purity.
Value Differences by Diamond Type
Due to rarity and purity factors, the different diamond types have the following value hierarchy on average:
| Diamond Type | Value Level |
|---|---|
| Type IIa | Highest |
| Type IIb | High |
| Type Ia | Medium to High |
| Type Ib | Lowest |
However, diamonds must be judged individually, and cut quality and carat size impact value at least as much as type alone. Smaller Type IIa diamonds can be lower value than larger Type Ia diamonds of better cut and proportions.
Identifying Diamond Types
Diamond typing technology has advanced to accurately sort natural diamonds into one of the 4 main types. Diamonds can be typed through a combination of methods:
Spectral Analysis
Spectrometers detect the presence and concentrations of nitrogen and boron impurities based on their interaction with UV, visible, and infrared light passed through the diamond. This distinguishes Type I, IIa, and IIb diamonds.
Phosphorescence Under UV Light
Diamonds emit differing phosphorescent glows under UV lamps based on their impurity content. Type IIa diamonds phosphoresce bright blue while Type Ib diamonds phosphoresce yellow.
Electrical Conductivity
Diamonds conduct electricity based on their impurity levels. Type IIa diamonds are electrically insulating while high-nitrogen Type Ib diamonds conduct current. Measuring resistance helps identify diamond type.
Advanced Technologies
New technologies like NMR spectroscopy (detecting impurities through magnetic spin) and LIBS spectroscopy (using lasers to excite phosphorescence) also type diamonds accurately without damaging them.
Summary of Diamond Types
In summary, here are the 5 major diamond types and their key characteristics:
Type Ia – Most common; contain small nitrogen impurities (
Type Ib – Rarest; significant nitrogen impurities (0.1% to 1%) giving yellow/brown color
Type IIa – Chemically pure; exceptional colorlessness and clarity
Type IIb – Extremely rare; contain boron giving blue coloration
Understanding diamond types provides insight into the geological origins and helps assess quality. While all diamond types can exhibit brilliance and fire, Type IIa diamonds are considered the most optically superior when evaluating diamonds on color and clarity. However, cutting quality is also an extremely important factor in determining overall diamond quality and value.
