What types of diamonds are there?
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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.
Diamond type
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Type I diamonds have 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 North 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 10% 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).
Diamond color
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Type II diamonds have very few if any nitrogen impurities. Pure (type IIa) diamond can be colored pink, red, or brown owing 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 diamonds. Type IIb diamonds, which account for ~0.1% of gem diamonds, are usually a steely blue or gray due to boron atoms scattered within the crystal matrix. These diamonds are also semiconductors, unlike other diamond types (see Electrical properties). Most blue-gray diamonds coming from the Argyle mine of Australia are not of type IIb, but of Ia type. Those diamonds contain large concentrations of defects and impurities (especially hydrogen and nitrogen) and the origin of their color is yet uncertain. Type II diamonds weakly absorb in a different region of the infrared (the absorption is due to the diamond lattice rather than impurities), and transmit in the ultraviolet below 225 nm, unlike type I diamonds. They also have differing fluorescence characteristics, but no discernible visible absorption spectrum.
Material properties of diamond
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Type I diamond has nitrogen (N) atoms as the main impurity, at a concentration of up to 1%. If the N atoms are in pairs or larger aggregates, they do not affect the diamond's color; these are Type Ia. About 98% of gem diamonds are type Ia: 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 usually of type Ib. Type Ia and Ib diamonds absorb in both the infrared and ultraviolet region of the electromagnetic spectrum, from 320 nm. They also have a characteristic fluorescence and visible absorption spectrum (see Optical properties).
Material properties of diamond
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There is a supplemental letter from the Gemological Institute of America stating that the diamond has been determined to be a Type IIa diamond. Type IIa diamonds are the most chemically pure type of diamond, and often have exceptional optical transparency. Type IIa diamonds were first identified as originating from India, particularly from the Golconda region, but have since been recovered in all major diamond-producing regions of the world. Famous examples of Type IIa diamonds are the 530.20 carat Cullinan I and the 105.60 carat Koh-i-noor.
The supplemental letter from the GIA is accompanied by a monograph from the Gemological Institute of America which features additional photographs, data collection charts and gemological research which details the rarity of the Elizabeth Taylor Diamond.
Elizabeth Taylor Diamond
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Different diamond types react in different ways to diamond enhancement techniques. Different types can coexist within a single stone; natural diamonds are often mixes of Type Ia and Ib, which can be determined by their infrared absorption spectrum.Not restricted to type are "green" diamonds, whose color is derived from exposure to varying quantities of ionizing radiation.
Diamond type
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Diamonds containing boron as a substitutional impurity are termed "type IIb". Only one percent of natural diamonds are of this type, and most are blue to grey. Boron is an acceptor in diamond: boron atoms have one less available electron than the carbon atoms; therefore, each boron atom substituting for a carbon atom creates an electron hole in the band gap that can accept an electron from the valence band. This allows red light absorption, and due to the small energy (0.37 eV) needed for the electron to leave the valence band, holes can be thermally released from the boron atoms to the valence band even at room temperatures. These holes can move in an electric field and render the diamond electrically conductive (i.e., a p-type semiconductor). Very few boron atoms are required for this to happen—a typical ratio is one boron atom per 1,000,000 carbon atoms.
Crystallographic defects in diamond
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Diamond is a good electrical insulator, having a resistivity of 100 GΩ·m to 1 EΩ·m (10 to 10 Ω·m). Most natural blue diamonds are an exception and are semiconductors due to substitutional boron impurities replacing carbon atoms. Natural blue or blue-gray diamonds, common for the Argyle diamond mine in Australia, are rich in hydrogen; these diamonds are not semiconductors and it is unclear whether hydrogen is actually responsible for their blue-gray color. Natural blue diamonds containing boron and synthetic diamonds doped with boron are p-type semiconductors. N-type diamond films are reproducibly synthesized by phosphorus doping during chemical vapor deposition. Diode p-n junctions and UV light emitting diodes (LEDs, at 235 nm) have been produced by sequential deposition of p-type (boron-doped) and n-type (phosphorus-doped) layers.
Material properties of diamond
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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.
Diamond color
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The DeYoung Red Diamond is a 5.03-carat unmounted diamond. It is a deep red color, with a slight tint of brown. Red diamonds are the rarest type of colored diamonds. The diamond is a modified round brilliant cut. The facets on the diamond's crown, which resemble kites, are split in two horizontally. This feature makes the DeYoung diamond more brilliant than other diamonds with an ordinary round brilliant cut. The DeYoung Red Diamond is the third-largest red diamond, behind only the 5.05-carat Kazanjian Red Diamond (second-largest) and the 5.11-carat Moussaieff Red Diamond (largest). Its clarity grade is VS-2 (Very Slightly Included). The diamond is a Type IIa diamond, meaning that it does not have any chemical impurities. Type IIa diamonds comprise only 1–2% of all naturally occurring diamonds.
DeYoung Red Diamond