Last updated on February 5, 2024
The diamond type classification is a valuable system that unravels the secrets behind a diamond’s colour, lattice defects, and origins. In this article, we will delve into diamond types, unveiling their unique properties and shedding light on their significance in the world of gemology.
What Is Diamond Type Classification?
Diamond type classification is a scientific method used to categorize diamonds based on their physical properties and the presence of chemical impurities. While diamonds ideally consist of carbon alone, the natural formation process often involves various geologic environments deep within the Earth, leading to the incorporation of impurities in the diamond’s chemical composition.
Diamond type classification takes into account not only the presence of chemical impurities acquired naturally during diamond formation but also trace elements added through treatments or laboratory synthesis. These impurities, along with lattice defects or optical defects, significantly influence a diamond’s colour and ultraviolet fluorescence reactions. The type and amount of these impurities and defects, as well as their arrangement within the diamond’s lattice, can have a profound impact on its appearance.
The original categorization of diamond types dates back to the 1930s when scientists introduced two categories: type I and type II. Over time, these categories have been further subdivided into type Ia, type Ib, type IIa, and type IIb, allowing for more precise classification and understanding of a diamond’s chemical composition and atomic structure. This detailed classification system enables gemologists and experts to discern the characteristics, behaviour, and unique properties of different diamond types.
Diamond type classification is vital for several reasons. Firstly, it aids in the identification of natural diamonds, synthetic lab-grown diamonds, and treated diamonds. By examining the impurities and physical properties, gemologists can distinguish between these origins and accurately determine a diamond’s authenticity.
Furthermore, the classification system helps in understanding and predicting a diamond’s behaviour when subjected to enhancement techniques. Different diamond types react differently to treatments such as heat or irradiation, making it essential for gemologists and experts to know the diamond’s type before applying any enhancements.
Type Ia Diamonds
Type Ia diamonds are the most abundant among natural diamonds, constituting approximately 95% of the total. These diamonds contain clustered nitrogen impurities within the carbon lattice, with concentrations of up to 0.3% (3000 parts per million). The presence of nitrogen clusters within the diamond’s structure gives rise to specific optical properties.
The absorption spectrum of nitrogen clusters in type Ia diamonds leads to the absorption of blue light, resulting in a pale yellow or nearly colourless appearance. Type Ia diamonds can be further categorized into two subcategories: IaA and IaB. This distinction arises from the arrangement of nitrogen atoms within the diamond lattice. In IaA diamonds, nitrogen atoms tend to form in pairs, while in IaB diamonds, nitrogen atoms form in clusters of four. This variation in nitrogen clustering affects the hue and intensity of the diamond’s colour.
In addition to the yellow colouration, type Ia diamonds can exhibit other hues, such as pink, violet, orange, red, brown, green, or blue. Type Ia diamonds can also exhibit additional optical phenomena, including fluorescence under ultraviolet light. Some type Ia diamonds may exhibit a fluorescence that causes them to appear bluish or milky when exposed to ultraviolet light sources.
Type Ib Diamonds
Type Ib diamonds, although accounting for only about 0.1% of all natural diamonds, are a distinct category within the diamond classification. These diamonds contain up to 0.05% (500 parts per million) of nitrogen, which is more diffusely distributed throughout the crystal lattice compared to type Ia diamonds.
The dispersed nitrogen atoms in type Ib diamonds result in unique optical properties. These diamonds not only absorb blue light like type Ia diamonds but also absorb green light, resulting in a deeper and more intense yellow or brown colour compared to type Ia diamonds.
It is noteworthy that type Ib diamonds are highly valued for their unique colour characteristics and rarity. The term “canary diamonds” often refers to these vivid yellow stones, reflecting their exceptional beauty and desirability.
Furthermore, type Ib diamonds have gained prominence in the realm of synthetic diamonds. Almost all high-pressure, high-temperature (HPHT) lab-grown diamonds fall into the type Ib category. This synthetic production of type Ib diamonds has contributed to their availability in the market, providing an alternative for those seeking the distinctive colour and attributes associated with this diamond type.
Type IIa Diamonds
Type IIa diamonds represent the pinnacle of purity and chemical composition in the world of diamonds. Comprising only 1-2% of all natural diamonds and approximately 1.8% of gem-quality diamonds, they are renowned for their exceptional clarity and lack of measurable nitrogen or boron impurities. This makes them the most chemically pure among all diamond types, allowing light to pass through with minimal hindrance and resulting in exquisite brilliance and sparkle.
One of the distinguishing features of type IIa diamonds is that they are colourless. However, it is worth noting that type IIa diamonds can also display subtle hues of grey, light brown, light yellow, or light pink. These colours may arise due to structural anomalies that occur during the diamond’s journey towards the Earth’s surface, resulting in imperfections caused by plastic deformation.
Type IIa diamonds are treasured for their rarity and their unique optical properties. These diamonds often command a premium price due to their scarcity and the unparalleled beauty they possess.
In addition to their captivating visual appeal, Type IIa diamonds also hold scientific significance. Their purity and unique composition make them valuable subjects for scientific research and experimentation. They provide insights into the natural formation processes of diamonds and the conditions under which they were created deep within the Earth’s mantle.
Type IIb Diamonds
Type IIb diamonds are an extraordinary and rare category, representing only about 0.1% of all natural diamonds. Their scarcity and unique characteristics contribute to their high value and desirability within the diamond market. These diamonds exhibit distinct qualities due to their low nitrogen content, comparable to type IIa diamonds, and the presence of significant boron impurities.
The boron impurities within type IIb diamonds have a serious impact on their colour and properties. The absorption spectrum of boron causes these diamonds to absorb red, orange, and yellow light, resulting in a light blue or grey colour. However, it is worth noting that some type IIb diamonds with lower levels of boron impurities can also appear colourless. The colour variations within type IIb diamonds depend on the concentration and distribution of boron atoms within their crystal lattice.
In addition to their unique colour, type IIb diamonds possess notable electrical properties. Unlike other diamond types, they are p-type semiconductors due to the presence of uncompensated electron holes. Even a small amount of boron, as low as 1 ppm, is sufficient to confer this property to the diamond. This exceptional electrical conductivity sets type IIb diamonds apart from other diamond types and makes them highly valued in specific applications that require conductive properties.
It is important to mention that not all blue-grey diamonds are categorized as type IIb. Some blue-grey diamonds, particularly those found in the Argyle mine of Australia, belong to the type Ia category. These diamonds contain significant concentrations of defects and impurities, such as hydrogen and nitrogen. The exact origin of their colour is still uncertain and subject to ongoing research.
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