Chemically, natural diamonds are classified into four types. While all diamonds are made of carbon, almost all contain minute quantities of other elements, interspersed within their crystal structures. These elements exist at the atomic level, contrast to inclusions, which can be seen by the naked eye or with a 10X loupe. The four main diamond types are as follows:
 
Type Ia: This is the most common class of natural diamonds, including up to 98 percent of all stones. They contain up to 0.3 percent nitrogen, with the nitrogen atoms clustered in aggregates within the carbon lattice. Such diamonds absorb blue light, and, depending on the concentration of nitrogen containing defects, will display a pale or more intense yellow color.
 
Type Ib: While very rare in nature, with only some 0.1 percent of natural diamonds belonging to this type, they nonetheless include almost all synthetic diamonds grown with the high pressure-high temperature (HPHT) method. In Type Ib diamonds the nitrogen atoms occur isolated throughout the carbon lattice. They absorb green light as well as blue light, and in general have a more intense color than Type Ia diamonds. Depending on the precise concentration of the nitrogen atoms, these diamonds can appear intense yellow ("canary"), orange or brown.
 
Type IIa: In many cases colourless, these stones contain miniscule, if any, quantities of non-carbon atoms and are considered the purest diamonds available. Making up 1-2 percent of all natural diamonds, they will only display color if absorption of light occurs due to crystal lattice imperfections. In such cases the diamond may display yellowish brown, brown or even pink or red colors.
 
Type IIb: Extremely rare in nature, these diamonds may contain even lower concentrations of nitrogen than Type IIa. However they contain boron impurities at the atomic level. About 0.1 percent of all natural diamonds are Type IIb. The presence of boron atoms means that the stones absorb red, orange and yellow light, and usually have a blue, blue-gray or gray color.