Diamond type
Encyclopedia
Diamond type is a method of scientifically classifying diamond
s 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.
Different diamond types react differently 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
In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...
s 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
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
atoms and so, unlike inclusions
Inclusion (mineral)
In mineralogy, an inclusion is any material that is trapped inside a mineral during its formation.In gemology, an inclusion is a characteristic enclosed within a gemstone, or reaching its surface from the interior....
, require an infrared spectrometer to detect.
Different diamond types react differently to diamond enhancement
Diamond enhancement
Diamond enhancements are specific treatments, performed on natural diamonds , which are designed to improve the gemological characteristics — and therefore the value — of the stone in one or more ways...
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.
- Type I diamonds, the most common class, contain nitrogenNitrogenNitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
atoms as their main impurity, commonly at a concentration of 0.1%. Type I diamonds absorb in both the infraredInfraredInfrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
and ultravioletUltravioletUltraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
region, from 320 nm. They also have a characteristic fluorescenceFluorescenceFluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
and visible absorption spectrum (see Optical properties of diamond).- Type Ia diamonds make up about 98% of all natural diamonds. The nitrogen impurities, up to 0.3% (3000 ppm), are clustered within the carbon lattice, and are relatively widespread. The absorption spectrum of the nitrogen clusters can cause the diamond to absorb blue light, making it appear pale yellow or almost colorless. Most Ia diamonds 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 ProvinceCape ProvinceThe Province of the Cape of Good Hope was a province in the Union of South Africa and subsequently the Republic of South Africa...
in South AfricaSouth AfricaThe Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
, whose deposits are largely Type Ia. Type Ia diamonds often show sharp absorption bands with the main band at 415.5 nm (N3) and weaker lines at 478 nm (N2), 465 nm, 452 nm, 435 nm, and 423 nm (the "Cape lines"), caused by the N2 and N3 nitrogen centersCrystallographic defects in diamondImperfections in the crystal lattice of diamond are common. Such crystallographic defects in diamond may be the result of lattice irregularities or extrinsic substitutional or interstitial impurities, introduced during or after the diamond growth...
. They also show blue fluorescenceFluorescenceFluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
to long-wave ultraviolet radiation due to the N3 nitrogen centers (the N3 centers do not impair visible color, but are always accompanied by the N2 centers which do). Brown, green, or yellow diamonds show a band in the green at 504 nm (H3 center), sometimes accompanied by two additional weak bands at 537 nm and 495 nm (H4 center, a large complex presumably involving 4 substitutional nitrogen atoms and 2 lattice vacancies).- Type IaA, where the nitrogen atoms are in pairs; these do not affect the diamond's color.
- Type IaB, where the nitrogen atoms are in large even-numbered aggregates; these impart a yellow to brown tint.
- Type Ib make up about 0.1% of all natural diamonds. They contain up to 0.05% (500 ppm) of nitrogen, but the impurities are more diffuse, the atoms are dispersed throughout the crystal in isolated sites. Type Ib diamonds absorb green light in addition to blue, and have a more intense or darker yellow or brown colour than Type Ia diamonds. The stones have an intense yellow or occasionally brownBrown diamondsBrown diamonds are the most common color variety of natural diamonds. The brown color makes them less attractive as gemstones and most are used for industrial purposes, however technical advances and improved marketing programs, especially in Australia, have resulted in brown diamonds becoming...
tint; the rare canary diamonds belong to this type, which represents only 0.1% of known natural diamonds. The visible absorption spectrum is gradual, without sharp absorption bands. Most blue-gray diamonds coming from the Argyle mineArgyle diamond mineThe Argyle Diamond Mine is a diamond mine located in the East Kimberley region in the remote north of Western Australia. Argyle is the largest diamond producer in the world by volume, although due to the low proportion of gem-quality diamonds, is not the leader by value. It is the only known...
of Australia are not of type IIb, but of Ia type; those diamonds contain large concentrations of defects and impuritiesCrystallographic defects in diamondImperfections in the crystal lattice of diamond are common. Such crystallographic defects in diamond may be the result of lattice irregularities or extrinsic substitutional or interstitial impurities, introduced during or after the diamond growth...
(especially hydrogen and nitrogen) and the origin of their color is yet uncertain. Almost all synthetic diamondSynthetic diamondSynthetic diamond is diamond produced in a technological process; as opposed to natural diamond, which is created in geological processes. Synthetic diamond is also widely known as HPHT diamond or CVD diamond, denoting the production method, High-Pressure High-Temperature synthesis and Chemical...
s are of Type Ib.
- Type Ia diamonds make up about 98% of all natural diamonds. The nitrogen impurities, up to 0.3% (3000 ppm), are clustered within the carbon lattice, and are relatively widespread. The absorption spectrum of the nitrogen clusters can cause the diamond to absorb blue light, making it appear pale yellow or almost colorless. Most Ia diamonds 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
- 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 225 nm, unlike Type I diamonds. They also have differing fluorescence characteristics, but no discernible visible absorption spectrum. The crystals as found tend to be large and irregular in shape. Type II diamonds were formed under extremely high pressure for longer time periods.
- Type IIa diamonds make up 1–2% of all natural diamonds (1.8% of gem diamonds). These diamonds are almost or entirely devoid of impurities, and consequently are usually colourless and have the highest thermal conductivityThermal conductivityIn physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....
. They are very transparent in ultraviolet, down to 230 nm. Occasionally, while Type IIa diamonds are being extruded towards the surface of the Earth, the pressure and tension can cause structural anomalies arising through plastic deformation during the growth of the tetrahedral crystal structure, leading to imperfectionsCrystallographic defects in diamondImperfections in the crystal lattice of diamond are common. Such crystallographic defects in diamond may be the result of lattice irregularities or extrinsic substitutional or interstitial impurities, introduced during or after the diamond growth...
. These imperfections can confer a yellow, brown, orange, pink, red, or purple colour to the gem. Type IIa diamonds can have their structural deformations "repaired" via a high-pressure high-temperature (HPHT) process, removing much or all of the diamond's color. Type IIa diamonds constitute a great percentage of Australian production. Many large famous diamonds, e.g. CullinanCullinan DiamondThe Cullinan diamond is the largest rough gem-quality diamond ever found, at .The largest polished gem from the stone is named Cullinan I or the Great Star of Africa, and at was the largest polished diamond in the world until the 1985 discovery of the Golden Jubilee Diamond, , also from the...
and Koh-i-NoorKoh-i-NoorThe Kōh-i Nūr which means "Mountain of Light" in Persian, also spelled Koh-i-noor, Koh-e Noor or Koh-i-Nur, is a 105 carat diamond that was once the largest known diamond in the world. The Kōh-i Nūr originated in the state of Andhra Pradesh in India along with its double, the Darya-ye Noor...
, are Type IIa. - Type IIb diamonds make up about 0.1% of all natural diamonds. In addition to having very low levels of nitrogen impurities comparable to Type IIa diamonds, Type IIb diamonds contain significant boronBoronBoron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...
impurities. The absorption spectrum of boron causes these gems to absorb red, orange, and yellow light, lending Type IIb diamonds a light blue or grey color, though examples with low levels of boron impurities can also be colorless. These diamonds are also p-typeP-type semiconductorA P-type semiconductor is obtained by carrying out a process of doping: that is, adding a certain type of atoms to the semiconductor in order to increase the number of free charge carriers ....
semiconductorSemiconductorA semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
s, unlike other diamond types, due to uncompensated electron holeElectron holeAn electron hole is the conceptual and mathematical opposite of an electron, useful in the study of physics, chemistry, and electrical engineering. The concept describes the lack of an electron at a position where one could exist in an atom or atomic lattice...
s (see Electrical properties of diamond); as little as 1 ppm of boron is enough for this effect. However, a blue-grey color may also occur in Type Ia diamonds and be unrelated to boron. Type IIb diamonds show distinctive infrared absorption spectrum and show gradually increasing absorption towards the red side of visible spectrum.
- Type IIa diamonds make up 1–2% of all natural diamonds (1.8% of gem diamonds). These diamonds are almost or entirely devoid of impurities, and consequently are usually colourless and have the highest thermal conductivity
Not restricted to type are green diamonds, whose color is derived from exposure to varying quantities of ionizing radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
.