Diamond type
Diamond type is a method of scientifically classifying diamonds by the level and type of their 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.
Diamonds as an investment
Diamonds in larger sizes are rare, and their price is dependent on the individual features of the diamond. Fashion and marketing aspects can also cause fluctuations in price. This makes it difficult to establish a uniform and readily understood pricing system. Martin Rapaport produces the Rapaport Diamond Report, which lists prices for polished diamonds. The Rapaport Diamond Report is relatively expensive to subscribe to and, as such, is not readily available to consumers and investors. Each week, there are matrices of diamond prices for various shapes of brilliant cut diamonds, by colour and clarity within size bands. The price matrix for brilliant cuts alone exceeds 1,400 entries, and even this is achieved only by grouping some grades together. There are considerable price shifts near the edges of the size bands, so a stone may list at $5,500 per carat = $2,695, while a stone of similar quality lists at $7,500 per carat = $3,750. This difference seems surprising, but in reality stones near the top of a size band (or rarer fancy coloured varieties) tend to be uprated slightly. Some of the price jumps are related to marketing and consumer expectations. For example, a buyer expecting a diamond solitaire engagement ring may be unwilling to accept a diamond.