Where did Kohinoor come from? Scientists have a unique big diamond theory

A new study found that giant diamonds formed in iron-rich regions deep beneath continents. The findings may help explain the origins of gems such as the Kohinoor and aid future diamond exploration.

In Short

• Chemical signatures pointed to ancient oceanic crust recycled into Earth’s mantle
• The team says magma interactions likely created conditions for massive diamond growth
• Researchers studied rare CLIPPIR diamonds, among the largest gem-quality stones known

A new scientific study exploring the mysterious origins of some of the world’s largest diamonds is raising an intriguing question: could legendary gems such as the Kohinoor have formed deep within strange iron-rich regions hidden inside Earth?

While the research did not specifically study the Kohinoor diamond, scientists say the findings may help explain how exceptionally large and valuable diamonds are born far beneath Earth’s surface.

The study, led by researchers at the University of Cape Town in South Africa and published in Nature Communications, focused on a rare class of giant gem-quality diamonds known as CLIPPIR diamonds, short for Cullinan-like, large, inclusion-poor, pure, irregular and resorbed diamonds.

These diamonds include some of the largest gems ever discovered, including the famous Cullinan Diamond, which weighed an astonishing 3,106 carats when unearthed near Pretoria in 1905.

Scientists found that the volcanic kimberlite rocks carrying such diamonds to the surface consistently passed through unusual iron-rich regions more than 150 kilometres beneath Earth at the base of the lithosphere.

These deep zones carried chemical signatures linked to ancient oceanic crust that had sunk into the mantle through subduction millions, possibly billions, of years ago.

“Our study shows that these extraordinary diamonds grew in an unusual iron-rich environment deep beneath the continents,” said Associate Professor Geoffrey Howarth, lead author of the study.

Researchers believe rising kimberlite magma interacted with these ancient iron-rich domains, creating conditions suitable for the

formation of giant diamonds.

The findings are significant because scientists have long struggled to understand how massive diamonds form compared with smaller, more common stones.

The study may also reignite fascination around the origins of the Kohinoor, one of the world’s most famous diamonds. Believed to have been mined centuries ago from the Kollur mines in present-day Andhra Pradesh during the Kakatiya dynasty, the Kohinoor is thought to have originally weighed around 793 carats before being cut multiple times through history.

Although its exact geological formation remains unknown, the Kohinoor likely originated in deep mantle conditions similar to other ancient large diamonds transported upward through kimberlite eruptions.

The research suggests Earth’s deep interior may preserve hidden pockets capable of producing giant diamonds under extraordinary pressure, temperature and chemical conditions.

Scientists say the work could also help future diamond exploration. By analysing the chemical “fingerprints” preserved in minerals brought up during volcanic eruptions, geologists may now better identify regions capable of hosting rare giant diamonds.

In essence, the study points to a remarkable possibility: some of humanity’s most treasured gems may owe their existence to fragments of ancient ocean floors buried deep inside Earth’s mantle over geological time.

- Ends