Diamond Type Classifications

Diamonds are categorized based on their atomic structure and chemical composition. The primary classification system separates diamonds into Type I and Type II, depending on the presence of nitrogen or other impurities in their crystal lattice. These distinctions impact a diamond’s optical properties, rarity, and even its formation process.

The presence or absence of nitrogen is the key factor in this classification. Type I diamonds contain nitrogen, while Type II diamonds do not. Within these two groups, further subcategories exist based on how nitrogen is arranged or whether other elements like boron are present. These variations affect a diamond’s color, transparency, and even electrical conductivity.

For gemologists and collectors, this classification system provides insight into a diamond’s origin and unique characteristics. For buyers, understanding diamond types can help in selecting stones based on purity, color potential, and value.

Types of Diamonds and Their Characteristics

Diamonds are classified into four main types based on the presence of nitrogen and boron:

• Type Ia – Contains aggregated nitrogen, usually resulting in a yellow tint. The most common type of natural diamonds.
• Type Ib – Contains single nitrogen atoms, often producing intense yellow or brown hues. Rare compared to Type Ia.
• Type IIa – Free of nitrogen, making them exceptionally clear and rare. These diamonds include some of the most famous stones in history.
• Type IIb – Contains boron, which gives them a blue color and electrical conductivity.

These classifications are based on the diamond’s atomic composition, not its visual appeal alone. While some types are more common in jewelry, others are prized for their rarity and unique optical properties.

Type Ia Diamonds

Type Ia diamonds are the most common among natural diamonds, making up the majority of stones found in the market. These diamonds contain aggregated nitrogen impurities, meaning nitrogen atoms group together within the crystal lattice rather than remaining isolated. This nitrogen content absorbs blue and violet light, often giving Type Ia diamonds a yellowish tint.

There are further subcategories within Type Ia:

• Type IaA – Nitrogen atoms form tight pairs that have little effect on color.
• Type IaB – Nitrogen atoms form larger clusters, which cause a stronger yellow or brown hue.

Because these diamonds are so prevalent, they are widely used in jewelry. Their color range varies, but those with stronger yellow or brown hues may be marketed as fancy-colored diamonds if the saturation is high enough.

Type Ib Diamonds

Type Ib diamonds are significantly rarer, accounting for less than 1% of natural diamonds. Unlike Type Ia diamonds, Type Ib stones contain isolated nitrogen atoms instead of nitrogen clusters. This structural difference alters light absorption, leading to more intense yellow or brown hues.

These diamonds often exhibit a deep canary yellow color, which is sometimes seen in high-value fancy-colored diamonds. The increased light absorption in the blue and green spectrum makes these diamonds appear more vividly colored than their Type Ia counterparts.

Most Type Ib diamonds are found in specific locations, such as the Argyle Mine in Australia and select mines in Africa. Due to their rarity and distinct coloration, they are highly sought after in the fancy diamond market.

Type IIa Diamonds

Type IIa diamonds are among the rarest and most chemically pure diamonds, making up less than 2% of natural diamonds. Unlike Type I diamonds, they contain no measurable nitrogen impurities, allowing them to be exceptionally clear and colorless. Their high purity also means they often exhibit superior optical transparency and brilliance.

These diamonds form under extreme geological conditions, often experiencing intense pressure and heat deep within the Earth’s mantle. This unique formation process contributes to their purity and, in some cases, results in irregular growth patterns, which can be detected under specialized examination.

While most Type IIa diamonds are completely colorless, some may develop a light brown, pink, or even purple hue due to plastic deformation in their crystal structure. Famous examples of Type IIa diamonds include:

• The Koh-i-Noor – A legendary diamond that has been part of royal collections for centuries.
• The Cullinan Diamonds – Large, high-quality diamonds cut from the famous Cullinan rough diamond.
• The Elizabeth Taylor Diamond – A rare and stunning example of a D-color Type IIa diamond.

Because of their rarity and purity, Type IIa diamonds are highly valued, particularly in high-end jewelry and investment-grade diamonds.

Type IIb Diamonds

Type IIb diamonds are even rarer than Type IIa diamonds, making up less than 0.1% of natural diamonds. Instead of nitrogen, these diamonds contain boron impurities, which cause their distinctive blue coloration. The presence of boron also makes them electrically conductive, a property unique to Type IIb diamonds.

The amount of boron in a Type IIb diamond determines the intensity of its blue hue. Some of the most famous blue diamonds belong to this category, including:

• The Hope Diamond – One of the most well-known diamonds in the world, featuring a deep blue color.
• The Blue Moon Diamond – A 12-carat Fancy Vivid Blue diamond sold for record-breaking prices.
• The Wittelsbach-Graff Diamond – A historic blue diamond with an intense saturation.

Due to their rarity, Type IIb diamonds are some of the most valuable colored diamonds in the world. While most are blue, some may exhibit shades of gray or violet depending on the concentration of boron.

Type I vs. Type II Diamonds: Key Differences

The distinction between Type I and Type II diamonds comes down to their chemical composition and optical properties. The presence or absence of nitrogen affects how these diamonds interact with light and impacts their rarity.

Key Differences Between Type I and Type II Diamonds

Feature	Type I Diamonds	Type II Diamonds
Nitrogen Content	Contains nitrogen (Type Ia: aggregated, Type Ib: isolated)	No measurable nitrogen
Commonality	98% of natural diamonds	Less than 2% of natural diamonds
Color	Often yellow or brown due to nitrogen absorption	Mostly colorless (IIa) or blue (IIb due to boron)
Transparency	Can have slight color tints	Often extremely clear and pure
Electrical Conductivity	Non-conductive	Type IIb diamonds conduct electricity due to boron
Famous Examples	Many commercial jewelry diamonds	Koh-i-Noor (IIa), Hope Diamond (IIb)

Which is Better?

Neither type is objectively "better"—it depends on the buyer’s priorities. Type IIa diamonds are valued for their purity and rarity, making them highly desirable for collectors and those seeking exceptional clarity. On the other hand, Type I diamonds are more widely available and often exhibit strong fluorescence, making them a common choice for jewelry. Fancy-colored diamonds, particularly vivid yellows, also tend to be Type I.

Collectors and investors often seek Type II diamonds due to their rarity and historical significance. However, Type I diamonds remain the standard choice in the jewelry market due to their availability and cost-effectiveness.

Are There Other Diamond Classifications?

Beyond the traditional Type I and Type II classifications, diamonds can also be categorized based on their origin and treatment methods.

Lab-Grown Diamonds and Their Classification

Lab-created diamonds fall into the same classification system as natural diamonds but may have different internal characteristics due to their growth process. The two main methods of lab diamond production are:

• High-Pressure High-Temperature (HPHT) – Mimics natural diamond formation but may introduce metallic inclusions.
• Chemical Vapor Deposition (CVD) – Produces high-purity diamonds, often classified as Type IIa due to the lack of nitrogen.

Treated and Enhanced Diamonds

Some natural diamonds undergo treatments that alter their appearance or improve clarity:

• HPHT Treatment – Used to remove brown coloration in Type IIa diamonds, making them whiter.
• Irradiation and Annealing – Alters color in Type I diamonds, producing shades of blue, green, or yellow.

While these treatments do not change a diamond’s type, they can enhance or modify its visual properties, making them important factors when evaluating a diamond’s natural characteristics.