The Types of Diamonds

All diamonds are judged on color, cut, clarity and carat, regardless of what their type is. Colored diamonds are more valuable if their color is richer. Type affects their value only because the types produce different colors, and certain colors are valued higher than others.
Type Ia diamonds are the most common, making up 98% of all diamonds. They contain traces of nitrogen, and absorb light in both the infrared and ultraviolet spectrums. Type Ia has up to 3% of nitrogen in their total makeup but usually only 1%. They are colorless or tinted yellow because the nitrogen in them absorbs blue light. Type Ia is further broken down into Type IaA and Type IaB depending on how the nitrogen is arranged. Type IaA have pairs of nitrogen atoms and appear colorless. Type IaB have clusters of nitrogen which gives them a yellowish color. The blue-grey diamonds from Australia’s Argyle Mine are Type Ia with more hydrogen and other impurities. The cause of their coloration is not known, however.
Type Ib has only 0.05% nitrogen content. They absorb green light as well as blue, giving them a richer yellow or brown color than Type Ia. Only 1% of natural diamonds are Type Ib, but many more synthetics are this type. Canary diamonds, known for their strong yellow color, are Type Ib.
Type IIa contains even fewer nitrogen impurities than Type Ib. They are colorless in their natural state, but as these diamonds are pushed toward the surface, the tension and pressure from the earth’s crust can stretch their structure like plastic. The deformations from this are called structural anomalies, and rather than ruining the diamond, they create brilliant colors like red, pink, purple, yellow, brown, or orange. The Koh-i-Noor is a type IIa diamond.
Type IIb have the lowest nitrogen content of any diamond. They can also contain boron impurities. This makes them absorb red and yellow light, and the diamonds look blue or grey. Type IIb diamonds are the only diamonds that function as a semiconductor because of their boron content. They are a p-type semiconductor, which means electron transfer through holes in the molecular structure, but only when certain types of atoms are applied to the diamond in a process called doping. The diamond itself remains neutrally charged even as the electrons are moving from molecule to molecule, and will not carry electricity to its wearer.