Have you ever wondered why some diamond jewelry and ornaments are worth more than others? Or, why do you have to pay considerably more to buy a particular diamond?
Well, that’s because not all diamonds are created equal and have the same value. Diamonds are usually graded and priced with the 4C’s –cut, clarity, carat, color. You’re probably aware of this already.
But there are also different types of diamonds. Basically, diamonds are classified based on their origin, physical and chemical properties to identify them better. Diamonds can be divided into two broad categories – natural and synthetic diamonds.
1. Type I Diamonds
Golden Jublee diamond
Natural diamonds containing any amount of nitrogen atoms (impurities) within the carbon lattice are labeled as Type I diamonds. Type I diamonds exhibit fluorescence — light emission in different colors and intensity — under ultraviolet wavelength. The nitrogen content in these diamonds varies between 0.05% to 0.3%.
Type I diamonds are further divided into Type Ia and Type Ib – based on the number of nitrogen impurities present in them.
Type Ia diamonds are the most common type of diamond found in nature. About 95 percent of all natural diamonds fall into this category. The number of nitrogen atoms present in the carbon lattice of Type Ia diamonds is as much as 0.3 percent or 3000 parts per million.
Apart from nitrogen atoms, other known impurities found in natural diamonds are hydrogen, boron, phosphorus, silicon, nickel, manganese, and tungsten. However, any element can be artificially injected into a diamond using a process known as ion implantation.
It is now established that nitrogen impurities are present in almost all naturally found diamonds but in different configurations. Type Ia diamonds contain nitrogen atoms in clusters. The nitrogen content and its composition (settings of nitrogen atoms) determine various material properties of a diamond, including the absorption of light in different wavelengths.
The molecular composition of Type Ia diamonds allows them to absorb blue light and thus have an almost colorless appearance. In some cases, these diamonds have pale yellow color as well.
Now, Type Ia diamonds can also be divided into two subtypes – Type IaA and Type IaB. The distinction is made based on advanced crystallographic and spectroscopic observations. But to put it in simple terms, the Type IaA diamonds are primarily colorless, while Type IaB diamonds can have green, yellow, and brown tint.
Most Type Ia diamonds are made up of both IaA and IaB elements. Perhaps the best example is ‘Cape diamonds’, or the Cape Series. All the faint yellow diamonds are called ‘Cape Diamonds.’ The term originated from the gems found in Cape Colony, South Africa.
Type Ib is one of the rarest natural diamonds found on earth. Approx. 0.1 percent of all diamonds fall into this category. Compared to Type Ia, Type Ib diamonds contain significantly lower nitrogen impurities, about 0.05 percent or 500 parts per million. More importantly, the nitrogen particles in Type-Ib diamonds are isolated and more widely dispersed.
The Type Ib gems absorb blue as well as the green light and thus have a much darker appearance than Type Ia diamonds. They are often bright yellow and brown in color.
A popular example of Type Ib diamond is the ‘Pumpkin diamond,’ a unique orange-colored diamond with a valuation of $3 million. All the fancier yellow-colored diamonds, also known as canary diamonds, belong to this category. It even includes some synthetic diamonds.
2. Type II Diamonds
The legendary Cullinan diamond(s)
Type II diamonds differ from Type I diamonds in several ways. The first and most important characteristic of Type II gems is they don’t contain any noticeable nitrogen impurities.
They have a different absorption and transmission spectrum that also affects their fluorescence characteristics. Moreover, Type II diamonds are believed to be formed under more intense pressure.
Type II diamonds are subdivided into Type IIa and Type IIb diamonds.
Type IIa diamonds are the purest form of diamonds found in nature, devoid of any impurities, including nitrogen. These diamonds have the highest thermal conductivity and are mostly colorless. About 2 percent of all-natural diamonds fall under this category.
In some instances, Type IIa diamonds can develop structural abnormalities or imperfections under intense pressure during their crystal growth phase. These imperfections can lead Type IIa diamonds to have a hint of yellow, orange, pink, or red color. However, the structural abnormalities in Type II diamonds can be corrected using HPHT or a high-pressure high-temperature process, thus also removing any color inclusions.
A large amount of Type IIa diamonds are found in Australia. Koh-i-Noor, the Cullinan, and Lesedi La Rona are some of the most famous examples.
Unlike Type IIa diamonds, which are completely devoid of any chemical impurities, Type IIb diamonds contain significant amounts of boron along with negligible nitrogen impurities. They are also one of the rarest diamonds. Only about 0.1 percent of all-natural diamonds are Type IIb.
The high amount of boron present in Type IIb diamonds causes them to absorb red and yellow light and thus usually have a blueish appearance. They are also found in blueish-grey color. However, if a Type IIa diamond has low amounts of boron impurities, then it’s more likely to be colorless.
You may have often heard that most natural diamonds are good insulators of electricity with the only exception of blue diamonds. Well, those blue gems are those with high amounts of boron impurities. Since boron is a good doping agent (dopant) for generating p-type conductivity, the Type IIb (blue diamonds) can be used as a semiconductor unlike any other type of diamond.
That being said, not all Type IIb diamonds are electrical conductors. Blue or blue-grey diamonds found in Australia’s Argyle diamond mine are like normal diamonds that don’t conduct electricity. Its believed that large amounts of hydrogen or nitrogen are responsible for this characteristic.
When natural diamonds receive any kind of advanced treatment to improve their visual gemological features, they are classified as enhanced diamonds. These treatments include laser drilling for clarity and removing black carbon, color irradiation to make colored diamonds much fancier, and vivid and fracture filling to repair cracks.
According to US FTC and World Jewelry Confederation guidelines, jewelers must disclose all information on diamond treatments during the sale.
3. Synthetic Diamonds
The ones we talked about in the above sections are all naturally formed diamonds created through various geological processes. On the other hand, synthetic diamonds are created in labs under a controlled environment. In other words, they are artificially created diamonds.
However, the chemical and physical properties of synthetic diamonds are almost similar to that of natural diamonds. Synthetic diamonds are made up of pure crystallized carbon in an isotropic form.
The first-ever recognized diamond synthesis was accomplished by ASEA (now ABB Group), a Swedish electrical engineering firm, in 1953. It was a result of a top-secret research project, code name ‘QUINTUS,’ conducted by the company to create lab-generated diamonds.
Interestingly, many diamond synthesis claims were reported even before 1953, though modern tests have refuted them.
Frédéric Moissan Image Courtesy: the United States Library of Congress
The earliest such claim was made by Scottish chemist James Ballantyne Hannay in 1879. Then in 1893, French chemist and Nobel laureate Frédéric Henri Moissan tried to produce diamonds using a small electric arc furnace. (What Moissan thought was diamonds was actually moissanite).
He did so by heating charcoal and iron at extremely high temperatures then rapidly cooling the molten iron with water. Through this process, Henri Moissan believed that he was able to generate the high pressure required to convert graphite into diamond. Other chemists performed similar experiments throughout the first half of the 20th century.
Applications of synthetic diamonds: Synthetic diamonds share many qualities with natural diamonds, including hardness and high thermal conductivity. Due to these properties (and better availability), synthetic diamonds have various applications, including – cutting tools, semiconductors, thermal conductors, and optical material.
4. Diamond simulant or Imitation Diamond
Diamond simulants, or imitations, are distinct from synthetic and natural diamonds as they are made of different materials (mostly artificial). They lack certain material properties of synthetic diamonds, such as high thermal conductivity and lipophilicity (oil and grease tend to spread across the surface of natural diamonds).
However, these simulants share gemological characteristics of natural diamonds, such as hardness, density, and dispersion. This allows them to be useful and a popular diamond alternative.
The most commonly used artificial diamond simulants are cubic zirconia (crystallized zirconium dioxide) and rhinestones (made from lead glass or acrylic polymers). The earlier forms of rhinestones have been known since at least the 18th century.
Due to its visual similarities and low costs, cubic zirconia was the most produced diamond simulant in the mid and late 1990s. In 1988, however, synthetic moissanite was introduced as a diamond alternative. Moissanite (natural silicon carbide) has been known since 1893, but it’s rarely found in nature.
Today, synthetic moissanite is widely favored instead of other diamond simulants due to its high thermal conductivity which is close to that of a natural diamond. Its competitions, rhinestones, and cubic zirconia have low thermal conductivity.
Frequently Asked Questions
How many types of diamonds (natural) are there?
Diamonds can be classified into two major types – one that contains nitrogen impurities (Type I) and one that doesn’t (Type II). Impurities refer to nitrogen atoms present inside the diamond crystals.
Based on the number of Nitrogen atoms they contain, the Type I diamonds are further divided into two subtypes- Type Ia and Type Ib.
Type II diamonds have different physical and chemical characteristics than Type I diamonds. They are also divided into two subtypes- Type IIa and Type IIb.
In total, there are four different types of diamonds that have been identified.
Which type of diamond is the rarest and most expensive?
The red diamonds are generally considered the rarest and most expensive diamonds on earth, even more so than blue and pink colored diamonds. At 5.11 carats, the Moussaieff Red Diamond is the largest known red diamond in the world. The Moussaieff is last valued at $20 million.
As we have discussed earlier, blue diamonds are also one of the rarest natural diamonds on earth. They belong to the Type IIb classification of diamonds. One of the largest and most famous blue diamonds is the Hope diamond (45.52 carats), with an estimated $200–250 million value.
What are the most expensive diamonds?
Among the world’s most expensive diamonds are – The Koh-i-Noor, The Cullinan, The Hope Diamond, and The Centenary Diamond – all above $100 million valuations.
How long does it take for a diamond to form?
Diamonds are formed deep inside the earth, where the temperature is extremely hot, and there is also intense pressure due to the overlying rocks. While scientists are still unable to accurately tell how much time it takes a diamond to form, they have reached the conclusion that diamond formation is not a continuous process.
A diamond formation may take as short a time as a few days or months to millions of years. It is possible that the growth of a diamond is interrupted due to changes in conditions, and the process is halted for thousands, millions, or even hundreds of millions of years to start again. Most large diamonds are millions of years old.