A Guide to Different Diamond Types

Most people are familiar with the diamond 4Cs —a method of assessing the attributes of a diamond. The 4Cs of diamonds refers to classifications based on the grading attributes of diamonds rather than the purely scientific factors. From a buyer’s perspective, the grading attributes help determine the value, cost, and overall appearance of the diamond, so they’re important to know and help buyers compare diamonds to each other. Our Diamond 4Cs guide lays out the basics of diamond color, clarity, cut and carat.

Beyond the 4Cs, there are other ways to classify diamonds that are typically lesser known, but nonetheless very important in gemology. The basic classifications start with their physical and chemical attributes. By doing this, one is able to assess how a diamond was formed, its authenticity, and whether or not it’s been treated.

In an ideal world, pure diamond is made of only a single element: carbon. But in reality, pure diamond is rarely found in existence because the natural formation process takes place in different geological settings and sometimes turbulent environments deep within the Earth’s crust. As a result, there are often chemical impurities found in a diamond’s chemical composition.

So, the different types of diamonds represent a scientific method of categorizing diamonds based on their physical properties and the type of chemical impurities they have. These classifications are very helpful when it comes to aiding gemologists in differentiating between natural, lab grown, and treated diamonds.

Technically speaking, there are two categories used to classify a diamond based on the presence or absence of nitrogen impurities:

• Type I - contains nitrogen impurities
• Type II - doesn’t contain nitrogen impurities

These two categories are further subdivided according to the arrangement of nitrogen atoms and the occurrence of boron impurities. There are four main subcategories making up the different diamond types.

Type Ia

Type Ia diamonds are estimated to make up about 95% of the world’s natural diamonds. They contain clustered nitrogen atoms, which, since nitrogen is the most abundant element in Earth’s atmosphere, it is entirely reasonable that nitrogen finds its way into a diamond’s lattice structure during formation the majority of the time.

These diamonds can vary in a range of color, or colorlessness, but most often have a yellowish tint because of the nitrogen clusters. They also tend to display stronger levels of blue fluorescence.

This category is further divided into two sub-sections: Type IaA and Type IaB. These two create a distinction between nitrogen atoms that form either in pairs (IaA) or in groups of fours (IaB). This will further affect the color hue of the diamond.

Type Ib

Type Ib diamonds are extremely rare and account for less than 0.1% of natural diamonds. Similar to the previous category of Type Ia diamonds, these also contain nitrogen in their crystal lattice formation.

The big difference between the two categories is that in Type Ib diamonds, the nitrogen atoms are scattered and isolated from one another instead of being clustered together, as in Type Ia diamonds. This configuration of the lattice structure means that diamonds will exhibit a more intense color hue like yellow, orange, or brown. Most fancy-color diamonds with intense color saturation fall into this category.

Type IIa

Type IIa diamonds make up roughly 1% of natural diamonds in the market and are chemically the purest and most highly sought after by investors and connoisseurs. These diamonds contain no measurable nitrogen or boron impurities. They are known for their D color, high clarity ratings, and absence of fluorescence. Some of the most famous diamonds in the world that have been coveted throughout history, like the Cullinan Diamond, are Type IIa diamonds.

They often have strange shapes because of the immense pressures under which they were formed, and while most are colorless, they can also be yellow, pink, red, or blue. However, unlike Type I diamonds where the color is a result of the presence of nitrogen or boron, Type IIa diamonds get their color from a deformation of the crystal lattice during the formation process. The Hope Diamond is a famous example of a Type IIa colored diamond.

Type IIb

Type IIb diamonds are another group of the rarest diamonds in the world, accounting for less than 0.1% of natural diamonds. They contain only boron impurities in their chemical composition, no nitrogen whatsoever. The presence of boron changes the physical characteristics, typically resulting in blue variations like bluish-gray and greenish-blue color hues.

Interestingly, the boron impurities mean that Type IIb diamonds can conduct electricity. This normally doesn’t happen because carbon atoms form covalent bonds in the diamonds, but the boron impurities interrupt these bonds in the crystal lattice structure. This also accounts for these diamonds exhibiting blue or red phosphorescence.

Different diamond types can get really technical from a gemological standpoint. And while the information can be fascinating and give you a deeper appreciation for your diamond, it’s not necessary to fully understand it in order to make a good diamond purchase. The most important distinction between diamond types for the shopper is a different set of classifications for types of diamonds. This one also has four categories: