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Diamond type is a method of scientifically classifying diamonds by their level and type of chemical impurities. Diamonds are separated into four types: Type Ia, Type Ib, Type IIa, and Type IIb. The impurities measured are at the atomic level within the crystal lattice of carbon atoms, and so unlike inclusions, require an infrared spectrometer to detect.^[1]

• Type Ia diamonds make up about 98% of all natural diamonds. In these, nitrogen impurities are clustered within the carbon lattice, and are relatively widespread. The absorption spectrum of the nitrogen clusters can cause the diamond to absorb blue light, making it appear pale yellow.

• Type Ib make up about 0.1% of all natural diamonds. They contain similar amounts of nitrogen to Type Ia, but the impurities are more diffuse. Type Ib diamonds absorb green light in addition to blue, and have a more intense or darker yellow or brown colour than Type Ia diamonds.

• Type IIa diamonds make up 1-2% of all natural diamonds. These diamonds are almost or entirely devoid of impurities, and consequently are usually colourless. Occasionally, while Type IIa diamonds are being extruded towards the surface of the Earth, the pressure and tension can cause the tetrahedral structure to become slightly misaligned, leading to imperfections. These imperfections can confer a yellow, brown, orange, pink, red, or purple colour to the gem.

• Type IIb diamonds make up about 0.1% of all natural diamonds. In addition to having levels of nitrogen impurities comparable to Type IIa diamonds, Type IIb diamonds contain significant boron impurities. The absorption spectrum of boron causes these gems to absorb red, orange, and yellow light, lending Type IIb diamonds a blue or grey colour, though examples with low levels of boron impurities can also be colourless.^[1]

See also

• Diamond colour

References