Types of Natural Diamonds

Types of Natural Diamonds

There are in fact many types of natural diamonds available. ‘Types’ are a way of scientifically classifying diamonds by their level and impurities. Some types are quite common, whilst some are extremely rare.

Diamonds are categorized into four types, type Ia, type Ib, type IIa and type IIb – these categories determine market cost and quality. An infrared spectrum is used to discover exactly what type the diamond is, in order to measure the level of impurities at the atomic level within the crystal lattice of carbon atoms.

Type I diamonds are the most abundant types available on the diamond market. The main impurity in this type is nitrogen at around 0.1%. Type I can be established as so by using infrared and ultraviolet light as they absorb it. This type is also visible on the absorption spectrum.

Type Ia is the most common natural diamond. It makes up around 90% of natural diamonds available. The concentration of nitrogen is around 0.3%, which makes the diamond absorb blue light, giving it a pale yellow colour or colourlessness.  Type Ia are often a combination of IaA and IbB (different atomic pattern for each), which are from the one of the biggest diamond industries in Africa, the Cape Province.

Type Ib consist of a lower concentration of nitrogen at 0.05% and are a much darker yellow or even brown. These are much rarer compared to type Ia as they make up roughly only 0.1% of the diamond population. The rarest type belongs to this category, the Canary diamond.

Type II diamonds are very large and oddly shaped maybe due to the fact that they have been formed under higher levels of pressure for a longer period than other types.  Unlike type I, they have no nitrogen impurities; however, they can still absorb infrared and ultraviolet at a certain level (below 225nm).  Opposite to type I, it does not have the characteristic of the visible absorption spectrum.

Type IIa are often the purest of diamonds as they are unlikely to have any impurities, which gives the diamond a colorlessness and the best level of thermal conductivity for diamonds. Type IIa make up around 1-2% of the diamond numbers, making them quite rare. However, with this type tends to get imperfections when pressurized out of the earth, which often results in a tint to the gemstone.

Type IIb has like IIa, very low levels of nitrogen impurities. However, they do have a high level of boron impurities, which gives them a grey-blue tint. They also lean towards the red on the invisible spectrum and characteristically show distinctive infrared absorption. Type IIb is by far the rarest type out there and has the unusual characteristic as acting as a p-type semiconductor.

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