CLIPPIR diamonds—a rare class of Cullinan-like, Large, Inclusion-Poor, Pure, Irregular, and Resorbed stones—represent less than 1% of all diamonds on Earth. According to research from the University of Cape Town, these gems originate more than 400km in the mantle transition zone, offering a unique geological window into the Earth’s recycling of carbon and ancient oceanic crust.
The Origins of Earth’s Largest Diamonds
Unlike standard gem-quality diamonds that form within the rigid mantle roots of ancient continents at depths of up to about 200km, CLIPPIRs are “superdeep” diamonds. Their formation is tied to the process of subduction, where tectonic plate movement drags ancient seafloor into the Earth’s interior. As this crust descends, heat and extreme pressure transform embedded carbon into diamond. Geologists at the University of Cape Town note that these stones are specifically linked to basaltic oceanic crust that underwent hydrothermal alteration before being forced into the deep mantle.
Did you know?
The 3,106-carat Cullinan diamond, discovered at South Africa’s Premier mine, is one of the largest diamonds ever recovered. More recent finds include the 1,111-carat Lesedi La Rona in 2015 and the 2,492-carat Motswedi diamond in 2024, both recovered from the Karowe mine in Botswana.
Chemical Fingerprints and Exploration Strategy
Identifying the primary source rocks for CLIPPIR diamonds has long challenged geologists because these stones are often found in river gravels far from their origin. Research into olivine—a mineral abundant in the mantle and found within kimberlite magmas—provides a solution. Kimberlites act as “natural elevators,” carrying diamonds to the surface. By analyzing the iron content and oxygen isotope signatures of olivine, scientists can create a chemical fingerprint of the deep mantle regions sampled by these magmas.
Future exploration efforts are now focusing on these specific chemical markers. In regions like Sierra Leone and Angola, where large diamonds have been found in river gravels, geologists suggest that kimberlites displaying these iron-rich signatures are the most promising targets for locating primary diamond sources.
The Role of Mantle Plumes in Diamond Transport
The journey of a CLIPPIR diamond is physically demanding. Because the iron-rich rocks hosting these diamonds are exceptionally dense, they cannot rise through the mantle passively. Researchers propose that mantle plumes—columns of superheated rock rising from the deep interior—are necessary to capture this dense material and push it toward the surface. This material is likely stored at the base of the continental lithosphere for hundreds of millions of years before being brought to the surface by rare, rapid volcanic eruptions.
Pro Tip:
When evaluating potential diamond-bearing regions, look for kimberlites that have been geochemically characterized for iron-rich signatures. This data is increasingly used to narrow down exploration zones in under-researched areas of Africa.
Frequently Asked Questions
What makes CLIPPIR diamonds different from ordinary diamonds?
CLIPPIR diamonds are “superdeep,” forming at depths more than 400km. They are distinct from ordinary diamonds, which form at shallower depths (up to about 200km) within stable continental roots.
Why are these diamonds so difficult to find?
They are extremely rare, making up less than 1% of all diamonds on Earth. Additionally, many are found in river gravels, which masks their primary kimberlite source.
How does oceanic crust relate to diamond formation?
Plate tectonics drag oceanic crust into the deep mantle. Once there, the carbon within this recycled material is subjected to extreme pressure and heat, which facilitates the formation of these exceptionally large diamonds.
Can we predict where the next large diamond will be found?
By analyzing the chemistry of olivine in kimberlites, geologists can identify areas that sampled the deep mantle transition zone, significantly increasing the precision of exploration in regions like Angola and Sierra Leone.
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