Examples of exceptional rough type IIa diamonds from the Letseng mine, Lesotho. These are the same kinds of diamonds as the ones examined in both of the studies mentioned above. The largest stone is 91.07 carats. (Photo by Robert Weldon; © GIA; courtesy of Gem Diamonds Ltd.)

Scientists at GIA (Gemological Institute of America) continue to delve deep into earth’s geologic history, using diamonds’ distinctive characteristics to go – virtually – where no scientist has ever gone. In two recent scientific papers, GIA researchers and their colleagues at other leading research institutions share their latest discoveries based on information gleaned from extremely rare and pure diamonds from very deep within the earth.

“Our unparalleled access to millions of diamonds each year, long-standing relationships with major research institutions and mission-driven dedication to sharing everything we learn make GIA uniquely able to help expand understanding of the fundamental forces that shape the planet,” said Tom Moses, executive vice president and chief laboratory and research officer. “Those same unique advantages support our continued innovations in diamond grading, including identification of treatments and automated diamond grading.”

A paper published this week in scientific journal Science Advances reveals that a hydrous rock called serpentinite, which forms in cracks in the ocean floor, is a critical ingredient in some of the largest and rarest diamonds that form at extreme depths. The research, co-led by Evan Smith from GIA and Peng Ni from the Carnegie Institution for Science, discovered an isotopic “fingerprint” of iron trapped in type IIa gem diamonds from Letseng, Lesotho. It is well understood that oceanic tectonic plates slide down into the mantle over millions of years, a process called subduction. This study reveals that some sinking ocean plates act like a giant conveyor belt capable of transporting water, carbon and other surface materials down into the interior of our planet— to depths of 360 to 750 km where these “super-deep” diamonds form. Understanding this deep recycling pathway is critical to understanding the evolution of the oceans and atmosphere.

In the most recent edition of American Mineralogist, Evan Smith and Wuyi Wang and their co-authors from the Department of Geosciences at the University of Padova, Italy, expand on their 2018 discovery of crowningshieldite, a new mineral named in honor of pioneering GIA researcher G. Robert Crowningshield. The studied example of crowningshieldite formed as part of a multi-component inclusion trapped in a diamond. It reinforces how unique diamonds are and adds to the growing list of exotic materials discovered within them.

Dr. Evan Smith’s research at GIA on very rare, large, pure diamonds that form between 360 and 750 kilometers (220 and 460 miles) deep in the earth was published in the scientific journals Science in December 2016 and in Nature in August 2018.