Study On Large Diamonds Offers Fascinating Insight Into Earth’s Mantle

Diamonds are worth a lot of money and are much-coveted by jewelers, as well as the customers who can afford them. But the largest of these diamonds hold particular interest to geologists, as they may offer clues as to how the Earth’s mantle works.

The study published this week in the journal Science and led by the Gemological Institute of America was based on established facts and previous discoveries on larger diamonds, suggesting that they have a different makeup than their smaller equivalents. The research also added some interesting findings on where larger diamonds can form, and what makes them different from the smaller ones.

“Some of the world’s largest and most valuable diamonds, like the Cullinan or Lesotho Promise, exhibit a distinct set of physical characteristics that have led many to regard them as separate from other, more common diamonds,” said study author Wuyi Wang, GIA director of research and development, in a press statement quoted by the Christian Science Monitor. “However, exactly how these diamonds form and what they tell us about the Earth has remained a mystery until now.”

Co-author Evan Smith, a Gemological Institute of America geologist, told NPR that diamonds are among the “most scientifically valuable” features of Earth. The reason being is that they come from the Earth’s mantle, hundreds of feet beneath the surface. The mantle holds so many mysteries that scientists have yet to figure out, and Smith added that he thought that large diamonds came from a completely different source due to their size and quality.

That had pushed Smith to conduct the new study, where he and his fellow researchers would look inside the large diamonds, examining the tiniest features that had cropped up when they were created deep below Earth’s surface.

“You really couldn’t ask for a better vessel to store something in. Diamond is the ultimate Tupperware.”

In the study, the GIA researchers analyzed eight chunks of diamond scraps, measuring about as small as the average fingernail. According to the CSMonitor, the scraps were then sliced open and ground into fine pieces, allowing them to study them with microphones, lasers, and other tools. They were then able to find a blend of several elements – carbon, iron, nickel, and sulfur – all housed in a fluid methane and hydrogen layer. Based on these findings, the GIA concluded that the diamonds were “formed under extreme pressure in oxygen-deprived patches of liquid metal.”

Although Smith had found the presence of methane in an inclusion to be peculiar, NPR states that he found the same blend of materials, and the same thin methane/hydrogen layer, in 38 out of 53 diamonds sent to the GIA for quality grading.

Another interesting note was the discovery that some of the samples came with mineral inclusions that proved that large diamonds can form as deep as 200 to 500 miles underneath Earth’s surface, which is substantially greater than the 90-120-mile depths where smaller diamonds are formed.

Speaking to NPR, Yale University mineral physicist Kanani Lee said that the new study contradicts the original theory that the Earth’s mantle consists a “thorough” mix of oxygen-rich rocks. But the diamonds, which range in age from about 100 million to one billion years old, help defy that explanation, suggesting that there are pockets in the mantle that weren’t affected by that mix.

“It further complicates things, but it makes us have to think more deeply about what’s going on in the planet because ultimately this does affect what we see up on the surface.”

All in all, the peculiar features observed by the GIA in their study of the large diamonds suggest that Earth may have had a more complex evolution process to become what it is today, a planet that can host life.

[Featured Image by Carl Court/Getty Images]