Scientists uncover deep-Earth origin of world’s rarest giant diamonds

An international team of scientists has uncovered the deep-Earth origins of some of the world’s rarest and most valuable diamonds, shedding new light on how giant Cullinan-like gems are formed beneath the planet’s surface.

The breakthrough study, led by researchers at the University of Cape Town and the China University of Geosciences, focused on a rare category of gemstones known as CLIPPIR diamonds – Cullinan-like, large, inclusion-poor, pure, irregular and resorbed stones – which include some of the largest and most valuable diamonds ever discovered.

Scientists found that the kimberlite rocks carrying these diamonds consistently originate from unusual iron-rich regions located more than 150 kilometres beneath Earth’s surface at the base of the lithosphere.

By analysing the chemical composition of the mineral olivine found within kimberlite formations, researchers identified distinctive isotopic signatures linked to ancient oceanic crust that was pulled deep into the mantle through subduction millions of years ago.

According to IOL, the findings reveal that these extraordinary diamonds crystallised under extreme pressures exceeding 11 gigapascals within the mantle transition zone deep beneath continents.

Researchers say the discovery could significantly improve understanding of geological processes occurring deep within Earth and may also help scientists identify new regions where rare giant diamonds could potentially be found.

The study further suggests that these iron-rich mantle domains play a broader role in shaping the chemical diversity of volcanic rocks across the planet.

The findings are particularly significant given the enduring fascination with the Cullinan Diamond, the largest diamond ever discovered, found near Pretoria in 1905 and weighing 3,106 carats, experts suggested.