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.
Argyle diamond mine
The diamonds produced at the Argyle diamond mine are of an average low quality. Only 5% of mined diamonds are of gem quality, compared to a worldwide average of 20% (Author Janine Roberts contends that the "near-gem" quality rating is subjective and misleading because these diamonds can be cut into gems if desired.); of the remaining 95%, they are about evenly split between classifications of "near gem quality" and industrial grade; 80% of Argyle diamonds are brown, followed by 16% yellow, 2% white, 2% grey, and less than 1% pink and green. Despite the low production volume of pink and red diamonds, the Argyle mine is the only reliable source in the world, producing 90 to 95% of all pink and red diamonds. Most Argyle diamonds are classified as type 1a (see material properties of diamond), and have low levels of nitrogen impurities, their colour resulting instead from structural defects of the crystal lattice. Argyle diamonds tend to fluoresce blue or dull green under ultraviolet light, and blue-white under X-ray radiation. The most common inclusion is unconverted graphite, followed by crystalline inclusions of orange garnet, pyroxene, and olivine.