Pink diamonds are in the news again. The Associated Press just published the news that “a big pink diamond of 170 carats has been discovered in Angola and is claimed to be the largest such gemstone found in 300 years. Called the ‘Lulo Rose,’ the diamond was found at the Lulo alluvial diamond mine.”
In 2017, NPR reported that the Pink Star diamond sold for $71million – a record price for a gemstone at the time. After cutting, the flawless diamond weighed in at 59.60 carats and measured 2.69cm by 2.06cm; it was 132.5 carats in rough state.
Years before, another pink diamond was discovered. The Daily News reported at that time that a12.76 carat pink diamond, named the Argyle Pink Jubilee, was found in Australia, the largest of the rare and precious stones ever found there. It has since been reported that the Argyle Pink Jubilee was donated to Melbourne Museum, home to the nation’s most comprehensive natural science display.
According to the AP article, Lulo is an alluvial mine which means the stones are recovered from a river bed, so the mining company is searching for the underground deposits, known as kimberlite pipes, which would be the main source of the diamonds.
We previously wrote how diamonds are most often found in kimberlite pipes, carrot-shaped, volcanic rock formations. Diamonds started out as carbon that crystallized deep in the earth under great pressure and temperature. Volcanic activity brought the diamonds to the Earth’s surface in kimberlite magma. Kimberlite pipes are not the only sources of diamonds; erosion of kimberlite deposits over many years can cause the release of diamonds and indicator minerals. Advancing and receding glaciers disperse and transport the eroded materials hundreds or thousands of miles away, creating alluvial deposits in which sometimes contain diamonds. However, most diamonds are found in the kimberlite itself.
Miners determine if a kimberlite pipe is worth pursuing by conducting regional sampling schemes and airborne geophysical surveys in a precise search area. Once a list of the best targets is assembled, grade analysis is done to find out if the kimberlite is sufficiently diamondiferous. Mining geologists can perform ore grade control with portable XRF analyzers to figure out where the most profitable ore bodies are, in terms of location and mineral concentration variability. Portable XRF analyzers can provide accurate sample data analysis for mining and exploration applications, including grade control, mine mapping, and identifying drill targets.
As we explained in a previous post, The Diamond Shortage: The Hunt for Kimberlite and New High Quality Synthetics, few kimberlite pipes yield enough diamonds to be worth the effort of mining them. So there is a large market for synthetic stones that resemble diamonds, as well as diamonds that have been treated to improve their appearance. These 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.
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. 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. The key use of FTIR in gemology is to provide evidence that a real diamond is natural and not treated or synthetic. (Read Analysis of Diamonds by FT-IR Spectroscopy to learn about several diamond analysis techniques using this technology.)
The color of pink diamonds formed from nature comes from distortion in their crystal structure, not from trace elements, If you want to know more about the color, the GIA published a great article on pink diamonds and their structure.
The Lulo Rose also will be cut down from its rough form, which could result in its weight dropping by up to half, according to the statement. But even if the Lulu Rose is reduced to 85 carats, the vivid pink stone looks primed to set a new sales record of its own.