Pink and red are caused by plastic deformation of the crystal lattice from temperature and pressure. Also not restricted to type are green diamonds, whose color is caused by GR1 color centers in the crystal lattice produced by exposure to varying quantities of radiation. However, a blue-grey color may also occur in Type Ia diamonds and be unrelated to boron. Type IIb diamonds, which account for 0.1% of gem diamonds, are usually light blue due to scattered boron within the crystal matrix these diamonds are also semiconductors, unlike other diamond types (see Electrical properties of diamond). Type IIa diamond can be colored pink, red, or brown due to structural anomalies arising through plastic deformation during crystal growth-these diamonds are rare (1.8% of gem diamonds), but constitute a large percentage of Australian production. They also have differing fluorescence characteristics, but no discernible visible absorption spectrum. Type II diamonds absorb in a different region of the infrared, and transmit in the ultraviolet below 225 nm (2.25 ×10 −7 m), unlike Type I diamonds. Type II diamonds have no measurable nitrogen impurities. They also have a characteristic fluorescence and visible absorption spectrum (see Optical properties of diamond). Type I diamonds absorb in both the infrared and ultraviolet region, from 320 nm (3.2 ×10 −7 m). Synthetic diamond containing nitrogen is Type Ib. If the nitrogen atoms are dispersed throughout the crystal in isolated sites (not paired or grouped), they give the stone an intense yellow or occasionally brown tint (Type Ib) the rare canary diamonds belong to this type, which represents only 10% of known natural diamonds. About 98% of gem diamonds are type Ia, and most of these are a mixture of IaA and IaB material: these diamonds belong to the Cape series, named after the diamond-rich region formerly known as Cape Province in South Africa, whose deposits are largely Type Ia. If the nitrogen atoms are in large even-numbered aggregates they impart a yellow to brown tint (Type IaB). If the nitrogen atoms are in pairs they do not affect the diamond's color these are Type IaA. Type I diamonds have nitrogen atoms as the main impurity, commonly at a concentration of 0.1%. Diamonds are scientifically classed into two main types and several subtypes, according to the nature of impurities present and how these impurities affect light absorption. Colored diamonds contain interstitial impurities or structural defects that cause the coloration pure diamonds are perfectly transparent and colorless. The 296 gems of the Aurora Pyramid of Hope as exhibited in the Natural History Museum in London under natural light.ĭiamonds occur in a variety of colors-steel gray, white, blue, yellow, orange, red, green, pink to purple, brown, and black. These from the National Museum of Natural History are a medium brown color. Main article: Diamond type The Hope Diamond, 45.52 carats (9.104 g), dark grayish-blue Jewellers diamonds in groups of similar colors. Numerous terms developed to describe diamonds of particular colors: golconda, river, jagers, cape, blue white, fine white, gem blue, brown, etc. Some early grading scales were I, II, III A, AA, AAA A, B, C. Without any co-operative development, these early grading systems lacked standard nomenclature and consistency. The Aurora Pyramid of Hope displays a spectacular array of naturally colored diamonds, including red diamonds.Ĭolor grading of diamonds was performed as a step of sorting rough diamonds for sale by the London Diamond Syndicate.Īs the diamond trade developed, early diamond grades were introduced. Of all colored diamonds, red diamonds are the rarest. For example, most white diamonds are discounted in price when more yellow hue is detectable, while intense pink diamonds or blue diamonds (such as the Hope Diamond) can be dramatically more valuable. Depending on the hue and intensity of a diamond's coloration, a diamond's color can either detract from or enhance its value. The color of a diamond may be affected by chemical impurities and/or structural defects in the crystal lattice. However, in reality almost no gem-sized natural diamonds are absolutely perfect. A chemically pure and structurally perfect diamond is perfectly transparent with no hue, or color.
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