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Diamond Types
What are the Different Types of Diamonds?

From Wikipedia

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.

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.

Type I diamonds, the most common class, contain nitrogen atoms as their main impurity, commonly at a concentration of 0.1%. Type I diamonds absorb in both the infrared and ultraviolet region, from 320 nm. They also have a characteristic fluorescence and visible absorption spectrum.

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 in South Africa, 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 centers. They also show blue fluorescence 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 color than Type Ia diamonds. The stones have an intense yellow or occasionally brown 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 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. Almost all synthetic diamonds are of Type Ib.

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 colorless and have the highest thermal conductivity. 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 imperfections. These imperfections can confer a yellow, brown, orange, pink, red, or purple color 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. Cullinan and Koh-i-Noor, are Type IIa.

Type IIb diamonds make up about 0.1% of all natural diamonds, making them one of the rarest natural diamonds and very valuable. In addition to having very low levels of nitrogen impurities comparable to Type IIa diamonds, Type IIb diamonds contain significant boron 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-type semiconductors, unlike other diamond types, due to uncompensated electron holes (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. Not restricted to type are green diamonds, whose color is derived from exposure to varying quantities of ionizing radiation.

100.20-Carat, Type IIa, Internally Flawless 'Perfect Diamond'
100.20-Carat, Type IIa, Internally Flawless 'Perfect Diamond'. Photo courtesy: Sotheby's
Is Buying a Type IIa Diamond a Smart Investment?

The method which scientifically classifies diamonds according to the level and type of chemical impurities inherent in the diamond is called "Diamond Type". Diamonds are categorized into four types: Type Ia, Type Ib, Type IIa, and Type IIb. These types represent the level of impurities measured at the atomic level, within the crystal lattice of carbon atoms, and require an infrared spectrometer to detect them, unlike the more common inclusions which can be seen by the naked eye or a diamond loupe. Not only is an infrared spectrometer needed to check what type a diamond is, a level of expertise in understanding what one sees when it is examined by an infrared spectrometer. Here at MDC Diamonds NYC have the tools and the knowledge to be able to accurately assess the type of diamond and can then appraise them appropriately.

100.20-Carat, Type IIa, Internally Flawless 'Perfect Diamond'
100.20-Carat, Type IIa, Internally Flawless 'Perfect Diamond'. Photo courtesy: AP
Detection of Diamond Type

When undergoing examination to determine diamond type, the diamond is wrapped in putty in order to prevent any outside light from disturbing the process of detection. At the same time a small hole is exposed in the bottom of the putty in order that the diamond will refract light. Then it is placed on the infrared spectrometer and covered with a special lens that allows the person examining to avoid looking directly at the very strong (and dangerous) UV light which is emitted by the machinery used to examine the diamond while still being able to determine the diamond type. We have expert jewelers who are experienced in this method of examining diamonds and are able to quickly check and asses each stone individually, especially when a customer has some concerns as to the type of stone.

It may appear that all diamonds are alike, at least in their basic make-up, however it is important to be aware that there are some notable differences within diamonds at the atomic level. One of the main factors that determine the color of a diamond is the particular characteristics of the trapped foreign objects. In most cases the foreign object is nitrogen (N), the trapped nitrogen atoms. Sometimes diamonds absorb the wavelengths of light which in turn produces a diamond that is light yellow or brown in color. Diamonds that have nitrogen as their primary impurity fall into the category of Type I diamonds, which make up 98% of all diamonds. Diamonds that have a presence of boron (B) or hydrogen (H) cause the diamond to be blue in color. Diamonds with boron as their impurity fall into the category of Type II diamonds.

The chemical buildup of a diamond will determine the classification of the diamond and it will be rated Type Ia, Type Ib, Type IIa, or Type IIb stone. Interestingly enough, one diamond can actually be classified in more than one specific type of diamond category, this is the case of most of the stones in the market today. These are the tests performed by the GIA when a diamond is sent in for certification.

In the 1930's it was discovered that different elemental impurities were responsible for the different colors of diamonds. The Nitrogen impurity which is the most common usually occurs in one of two ways. Either in large groups (aggregates) of nitrogen, or as single nitrogen atoms scattered within the diamond's crystal lattice. These two forms of impurities are further broken down into two sub-groups, Type Ia and Ib.

100.20-Carat, Type IIa, Internally Flawless 'Perfect Diamond'
100.20-Carat, Type IIa, Internally Flawless 'Perfect Diamond'. Photo courtesy: Reuters
Type Ia Diamonds

Type Ia diamonds are those diamonds that contain nitrogen in aggregates (or large groups). This can be broken down into other sub categories. When these aggregates occur in pairs within the diamond lattice, this is called Type IaA. When they occur in aggregates of four (4) nitrogen atoms they are classified as Type IaB. These types cannot absorb any of the wavelengths of visible light. However, when nitrogen occurs in groupings of three (also called Type IaN3 center), the nitrogen groups absorb the visible light within the blue end of the spectrum, causing a yellow color to appear in the diamond.

Therefore, the nitrogen in Type IaA and IaB diamonds does not affect the diamond's color, whereas the nitrogen of Type IaN3 center does affect the diamond's color, causing it to have a yellow tint.

Type Ib Diamonds:

Type Ib diamonds are far less common than type Ia. Type Ib account for less than 0.1% of all natural diamonds. Type Ib diamonds are diamonds that contain single nitrogen atoms scattered throughout the diamond's crystal lattice framework. It is this scattering of single nitrogen atoms, which allows the absorption of visible light from the blue end of the spectrum, thus causing an intense yellow color to form. True Canary Yellow Diamonds which are quite rare and valuable are of this type. This atomic formation also causes the formation of Brown and Yellow-Green Diamonds.

Type IIa Diamonds:

Why is a type IIa diamond a better investment diamond than other diamonds?

Less than 1% of the world's diamonds are Type IIa, also called "Golconda Diamonds", named for the famous Indian mines that gave the world some of its first truly great diamonds in the 16th and 17th century.). Scientifically speaking, Type IIa diamonds are almost pure carbon diamonds, containing no significant amount of nitrogen in the crystal lattice. Nitrogen is the impurity in diamond that imparts a yellowish hue. The lack of yellow makes for a pure very valuable colorless (D, E or F) color diamond. Type II diamonds are also divided into two categories, Type IIa and Type IIb. These sub-groups are further categorized separated into two groups, Type IIa diamonds which are capable of conducting electricity and Type IIb diamonds which are not able to conduct electricity.

Type IIa diamonds are colorless, unless they have an inclusion or defect in the structure of the diamond that would allow light absorption to occur. Diamonds of this type can be gray- brown, yellow, pink, light blue, or light green (the two last colors arising from radiation exposure.) however, most of the time they are the perfectly colorless diamonds that most people are looking for. This is due to the fact that their structure does not easily absorb short-wave ultraviolet light wavelengths, but instead allows the light to pass through. Such famous diamonds as the Cullinan (the world's largest cut diamond, found in the South African Premier Mine in 1905) and the Koh-i-Noor (Urdu for "Mountain of Light"), which was found in India and now rests in the Tower of London, are type IIa diamonds.

These facts make this diamond type more sought after by the rich and famous, such as the 33.19ct Type IIa "Elizabeth Taylor Diamond" (formerly known as the "Krupp Diamond") that was purchased in 1968 (before anyone knew that there were different types of diamonds) for $300,000 sold recently at auction for 8.8 million dollars.

Why One Should Choose a Type IIa Diamond

Type IIa diamonds have many special characteristics both on a "geological" level as well as what can be seen by the eye. This causes them to be more sought after and each one to have a unique story. This also causes them to be more valuable, making them a smart choice for an investment. Most of the types IIa diamonds are larger diamonds, mostly over 10 carats. An increase in size signifies a substantial increase in value and price. On average, a diamond that is certified as type IIa is valued at between 2-3% more than the same diamond that is not certified as type IIa.

For example a 5.50ct D color IF (internally flawless) round cut diamond costs on an average retail website $800,000 while the same diamond if it were Type IIa it would cost around $825,000. Many times the customers who are looking for the highest quality diamonds such as VVS1 or IF clarity, D color, an Excellent or Ideal cut, with no fluorescence, will choose the stone that is Type IIa as in order to own what they perceive to be a more "perfect" diamond.

Type IIb Diamonds

Type IIb diamonds are similar to Type IIa diamonds in terms of the lack of, Nitrogen atoms which are contained in the structure of these stones. However, they are infused with the addition of Boron, which makes these stones so unique. The Boron element is known to be the greatest cause of the desirable blue tone within the stone. In fact, colorless stones often look better than their actual color grade and fancies of this class are often found with light blue or gray dominant colors.

Elizabeth Taylor Diamond'
The "Elizabeth Taylor Diamond" (formerly known as the "Krupp Diamond"), a 33.19-carat Type IIA diamond. Purchased for $300,000 in 1968 by Richard Burton, the ring became one Elizabeth Taylor's most cherished white diamonds; one she wore nearly every day. Of the ring, she once said, "[It] gives me the strangest feeling for beauty. With its sparks of red and white and blue and purple, and on and on, really, it sort of hums with its own beatific life." The Asscher-cut diamond ring recently sold at auction for a whopping $8.8 million.
 
Summary

Type I diamonds are the most common. They represent 98% of all natural diamonds and have detectable traces of Nitrogen.

Type Ia diamonds contain clusters of Nitrogen atoms throughout the crystal structure of the stone. They tend to emit a yellowish tone.

Type Ib diamonds contain Nitrogen atoms as well. These atoms are all singular as opposed to clustered groups. These stones are 0.1% of all diamonds and emit a strong yellow, orange, brown and even green color tone.

Type IIa diamonds are the most valuable and consequently are very collectable items. They contain either very little or no Nitrogen atoms in the crystal structure of the stones. White stones are exceptionally colorless and fancy colored diamonds are often found with a brown, purple, or pink tone. They represent only 1% - 2% of all diamonds.

Type IIb diamonds contain elements of Boron within the structure. As a result, they often emit a blue or gray tone. They represent only 0.1% of diamonds. And consequently they are also very valuable.

In short, Type IIa and Type IIb stones are the most unique and therefore collectable items. Especially in the case of fancy colored diamonds. Since no stones are exactly alike, it is important to assess each diamond individually. One should never assume that a diamond will be perfect because it is graded a specific class or that it is worthless because it is of the more common type stones.

Maybe the diamond you are wearing right now is a type IIa and you don't even know it. Take it to your local jeweler or send it to a lab to get it check and certified if it is you just made a huge amount of money just by reading this article.

Buying Type IIa Diamonds from MDC Diamonds NYC

If you are interested in purchasing a Type IIa (or any other type of diamond) in any shape size or color, please contact our experienced diamond experts so that they can help you source the diamond of your choice at the best possible price. Toll free 1-866-235-4315 or e-mail


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January 12, 2017

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