A Diamond the Size of a Tennis Ball

If you are a fan of tennis and followed any of the Wimbledon tennis matches this past week, you might know that over 50,000 tennis balls are used during the Championship period.  According to the official Wimbledon site, the balls are stored at 68 deg F, new balls are brought in after the first seven games (to allow for warm-up), then after every 9 games, and that yellow balls were used for the first time in 1986.  The International Tennis Federation states the acceptable range for ball diameter is 6.54 cm to 6.86 cm respectively for a Type 2 ball (around 2.7 inches).

Coincidentally, that is also the approximate size of the world’s largest uncut diamond that failed to sell at Sotheby’s Auction last week.  Last year a Canadian mining company found a three-billion-year-old diamond the size of a tennis ball.  According to an ABC News report, “The 1,109 carat white diamond did not meet the reserve price, or minimum acceptable bid, which was not specified by Sotheby’s auction house in London. The rough stone was expected to fetch at least $70 million, but the bidding stopped at $61 million, Sotheby’s said.

“The rock was discovered in November by the Lucara Diamond Corp. in the company’s Karowe mine in north-central Botswana. It’s the largest diamond to be recovered in the southern African nation and the biggest find worldwide in over 100 years. The tennis-ball-size stone, named Lesedi la Rona (Our Light in Setswana), is thought to be 3 billion years old.”

Our previous post, The Diamond Shortage: The Hunt for Kimberlite and New High Quality Synthetics, talked about how rare it is to find a diamond, nevermind one of such size or significant value. Most diamonds are found in kimberlite pipes, and few pipes yield enough diamonds to be worth the effort of mining them. (Read Kimberlite: A Girl’s Best Friend? for more details.)

Why didn’t it sell?  Has the buying public fallen out of ‘love’ with the girl’s best friend? Was the owner just asking too much money in an economy short on cash? Or has the glimmering idea of owning that special mineral dulled a bit with the rise in synthetic diamond sales.

Synthetic stones have become big business. These include high-pressure high-temperature (HPHT) diamonds and laboratory-grown diamonds formed by Chemical Vapor Deposition (CVD), techniques which have improved to the point that these products are nearly indistinguishable from natural diamonds. Today, the identification of synthetic and treated diamonds has become one of the major challenges for the gem industry. If they didn’t know the history, and Lesedi la Rona was on display, would anyone believe it was a mined diamond, or would it be assumed that it was created by technology?  Can technology even produce a synthetic diamond of such size?  If so, what’s next?  Basketball size synthetic diamonds?

As we learned in a previous post, FT-IR spectroscopy can be a useful tool to determine whether diamonds are natural and what type they are. FT-IR (Fourier Transform Infrared) 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.

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.

It is difficult to determine if a diamond is synthetic or treated. The infrared peaks corresponding to the nitrogen aggregates or presence of other elements can be used to provide valuable evidence that a stone is not natural. Numerous gemological laboratories employ FT-IR on a daily basis to characterize diamonds and other gemstones, but it’s no grand slam. FT-IR is used extensively to provide “evidence” about treated or synthetic diamonds, but does not provide a definitive answer because of the tremendous variation in natural stones.

Another difficulty in this particular case 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. On the other hand, synthesizing a gem quality stone greater than a couple of carats would be extremely difficult, and very expensive.

For a high value gemstone you really want an experienced gemologist to make a diagnosis based on the results of multiple tests — FT-IR being one of the most useful. 

And the Lesedi la Rona is certainly one of high value, worthy of being presented on a gilded silver Venus Rosewater Dish.

 

Additional Resource:

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.