Last year we wrote about the world’s largest uncut diamond that failed to sell at auction. The 1,109 carat, tennis-ball-sized rock, which had been discovered by the Lucara Diamond Corp. in the company’s mine in north-central Botswana, was thought to be 3 billion years old.
Well, it has finally sold…for $53 million. That’s nearly $47,777 per carat.
A diamond that size had to have its skeptics, and I’m sure the analysis methods were scrutinized by the buyer, seller, and everyone in the diamond industry. Real diamonds are formed in the earth over the course of thousands of years, under crushing pressures and intense heat. Synthetic stones, however, include high-pressure high-temperature (HPHT) diamonds and laboratory-grown diamonds formed by Chemical Vapor Deposition (CVD), techniques which produce products nearly indistinguishable from natural diamonds.
As we mentioned in a previous article, although portable X-Ray Fluorescence cannot measure carbon, the technology can be deployed to measure Zr, and thus, to distinguish between the diamond look-alike, cubic zirconia, and real diamonds.
Fourier Transform infrared (FTIR) spectroscopy can be used to analyze the impurities in diamonds to help confirm if the diamond is synthetic or if it has been treated. It can be a useful tool to determine whether diamonds are natural and what type they are. FT-IR spectroscopy produces an infrared absorption spectrum that represents a ﬁngerprint of the sample with absorption peaks which correspond to the frequencies of vibrations between the bonds of the atoms making up the material. Because each element is a unique combination of atoms, no two compounds produce the exact same infrared spectrum. (Read more about synthetics diamonds here. )
Diamonds are unique among gemstones because they are composed of a single element (carbon), while virtually all other gems contain multiple elements including significant amounts of oxides. The infrared spectrum of diamond is equally unique and can be used to easily confirm that a stone is actually a diamond. A diamond consists of crystalline carbon and the extreme conditions required to create them also provide a way for trace amounts of other elements to be trapped in the crystal matrix. The most important trace element is nitrogen, which can be found in different forms in the diamond crystal. These nitrogen aggregates create unique features in the infrared spectrum and are key in classifying diamonds. Hydrogen, boron and carbonates are other important trace elements, all of which have identifiable features in the infrared spectral region.
One difficulty the analysts probably ran into is that the diamond is so big it would be difficult to get a spectrum since FT-IR looks at the infrared light transmitted through the sample. If FT-IR was used for this particular stone, it was probably for the purpose of characterizing it. However, synthesizing a gem quality stone greater than a couple of carats would be extremely difficult, and very expensive.
We’re not sure how it was analyzed or valued. For this particular gemstone I’m sure they used many experienced gemologists and several lab analysis techniques to make a diagnosis based on the results of multiple tests. When you’re spending over $50 million on a stone, the cost of multiple tests is miniscule in comparison.
What we do know? It’s game, set, match, sold.
Read Analysis of Diamonds by FT-IR Spectroscopy to learn more, and to read several examples of how the combination of an FT-IR spectrometer with an optimized accessory provides multivariate statistical analysis techniques to provide a rapid, reliable information source of great importance to classifying gemstones.