It’s been a sparkly fall at the Smithsonian’s National Museum of Natural History. We recently welcomed 500 carats of rough diamonds into the National Gem and Mineral Collection thanks to a generous donation from Rio Tinto. The gemstones arrived in a kaleidoscope of colors, including rare pink diamonds. Take a look for yourself!
These dazzling beauties were extracted from Rio Tinto’s Argyle Mine in remote northwest Australia, an area known for naturally colored diamonds. Unlike most polished diamonds that you might see in a jewelry store, these stones were removed from the earth and kept in their natural, “rough” state. For our team of mineral scientists, that’s the perfect form in which to study them.
Why do scientists study diamonds? For one thing, they offer a unique window into the geological history of the planet. Diamonds typically formed more than 100 miles deep in the Earth and provide an exceptional window into the geologic processes and conditions that took place there 2–3 billion years ago. Dr. Jeffrey Post, curator of the National Gem and Mineral collection, specializes in telling the stories of diamonds and other gems by searching for clues about their origins. In the case of the Rio Tinto crystals, the rough diamonds carry tiny mineral grains that might be unique to diamonds only found in the Argyle mine. If future unknown gems with the same mineral fingerprint are discovered, scientists will know that they also originated in the Kimberly region of Australia.
Diamond colors add another chapter to the history of the Earth’s deep past. Post and his colleagues have discovered that blue diamonds, like the museum’s 45.52 carat Hope Diamond, form when boron becomes trapped in a crystal’s molecular structure while yellow diamonds result when nitrogen atoms swap places with carbon. Green, a very unusual color in diamonds, occurs when crystals form in rocks exposed to radiation. Fun fact: green diamonds are thought to be the inspiration for kryptonite in the Superman series!
The cause of the pink color found in many of the Rio Tinto gems remains a bit of a mystery, but Post is leading the charge to find answers. He recently conducted research confirming that this striking color is likely the result of a shock event that took place in the gem’s history, either in the mantle or during transport to the surface of the Earth. The result: changes in the structures of pink diamonds that interact with light to produce colors ranging from brown to pink.
By Kathryn Sabella, Press Officer, National Museum of Natural History