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Diamond color
A chemically pure and structurally perfect diamond is perfectly transparent with no hue, or ''color''. However, in reality almost no gem-sized natural diamonds are absolutely perfect. The color of a diamond may be affected by chemical impurities and/or structural defects in the crystal lattice. Depending on the hue and intensity of a diamond's coloration, a diamond's color can either detract from or enhance its value. For example, most white diamonds are discounted in price when more yellow hue is detectable, while intense pink or blue diamonds (such as the Hope Diamond) can be dramatically more valuable. Out of all colored diamonds, red diamonds are the rarest. The Aurora Pyramid of Hope displays a spectacular array of naturally colored diamonds, including red diamonds.
==Possible colors==
(詳細はnitrogen atoms as the main impurity, commonly at a concentration of 0.1%. If the nitrogen atoms are in pairs they do not affect the diamond's color; these are Type IaA. If the nitrogen atoms are in large even-numbered aggregates they impart a yellow to brown tint (Type IaB). 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 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 0.1% of known natural diamonds. Synthetic diamond containing nitrogen is Type Ib. Type I diamonds absorb in both the infrared and ultraviolet region, from . They also have a characteristic fluorescence and visible absorption spectrum (see Optical properties of diamond).
Type II diamonds have no measurable nitrogen impurities. Type II diamonds absorb in a different region of the infrared, and transmit in the ultraviolet below , unlike Type I diamonds. They also have differing fluorescence characteristics, but no discernible visible absorption spectrum. 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. 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). However, a blue-grey color may also occur in Type Ia diamonds and be unrelated to boron. 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.〔
Pink and red are caused by plastic deformation of the crystal lattice from temperature and pressure. Black diamonds are caused by microscopic black or gray inclusions of other materials such as graphite or sulfides and/or microscopic fractures. Opaque or opalescent white diamonds are also caused by microscopic inclusions.〔http://nhminsci.blogspot.ca/2013/01/color-in-diamonds.html〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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