Depending on the presence of chemical impurities in diamonds, which occur at the atomic level within the crystal lattice of carbon atoms and requires an infrared spectrometer to detect, diamonds are scientifically classified according to their types.
Type Ia diamonds though constitute almost all the Earth-mined diamonds, they contain nitrogen impurities which affects the light absorption and in turn sometimes gives color to the diamonds. Whereas, Type IIa, though constitute a very small portion of all available diamonds, are devoid of any measurable impurities, are usually colorless and have the highest thermal conductivity, making them the highest purity and most valued diamond type. Many large famous diamonds including Cullinan, Koh-i-Noor et al are Type IIa diamonds.
Some famous Type IIa diamonds
Found in 1905 near Pretoria, South Africa, the rough uncut Cullinan diamond weighed 3,106.75 carats. The original rough stone was later cut into several polished diamonds including the 9 large gems – Cullinan I to Cullinan IX. Cullinan I, also known as the ‘Great Star of Africa’ is the largest polished colorless diamonds and weighs 530.4 carats (The largest diamond in the world – Golden Jubilee Diamond discovered in 1985 and weighing 545.67 carats is a brown colored diamond), while Cullinan II, also called ‘Second Star of Africa’ weighs 317.4 carats. Both the diamonds are in the crown jewels of UK.
The famous Koh-i-Noor (Persian for Mountain of Light) diamond was found near Kollur in India. Originally weighing 793 carats and once the largest known diamond in the world, its size has been reduced to 105.6 carat after many cutting and polishing. Koh-i-Noor diamond passed several hands through dynasties, rulers and invasions and eventually landed up as a British Crown Jewel. It currently is a part of the Crown of Queen Elizabeth.
Elizabeth Taylor diamond
Formerly known as Krupp diamond, the Elizabeth Taylor diamond, a 33.19 carat Asscher cut Type IIa diamond, was bought by Elizabeth Taylor’s husband – Richard Burton in 1968 at a NY auction for USD 300,000. The diamond became an important part of Taylor’s collection and she wore it as a ring. In 2011, the Elizabeth Taylor diamond was sold by Taylor’s estate for USD 8.8 million.
Archduke Joseph diamond
Originally weighing 78.54 carat, the Archduke Joseph diamond, a antique cushion-shaped, colorless, brilliant, Type IIa, was purchased by Molina Jewelers of Arizona in 1990s and was recut to 76.45 carat for improved clarity and symmetry. The IF, D grade is the largest DIF diamond ever graded at GIA. Recovered in India’s Golconda mines, the Archduke Joseph diamond’s first recorded owner was Austria’s Archduke Joseph August who had deposited the diamond in a Hungarian bank vault in 1933.
Recovered from the legendary Golconda region in India, the Regent diamond was found in Kollur mine in 1698 and originally weighed 410 carats. After series of sales, the diamond ended up with the French Regent – Phillipe II, Duke of Orleans in 1717. By that time, the diamond weighed 140.64 carats after a cushion brilliant cut. The Regent diamond was set in Louis XV’s coronation crown in 1722, new crown for Louis XVI’s coronation in 1775 and also used to adorn Mary Antoinette’s hat. It is currently on display at the Louvre, with an estimated value of GBP 48 million.
Similarly, there are many other famous Type IIa diamonds including The Star of the South, Winston legacy, The Agra, Darya-i-Noor, Beau Sancy and so on. Type IIa diamonds are either way very rare and declining production of Earth-mined diamonds make them even rarer. However, with advent of technology, it is now possible to grow 100% pure Type IIa diamonds in a lab. Most of the CVD Lab-grown diamonds are Type IIa, taking them from the exclusive hands of royalties and aristocracies to the reach of common man.