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Rare diamondiferous peridotite from the Udachnaya diamond mine. Image credit: Lawrence Taylor.


“It is a wonder why this rock has more than 30,000 colorless, octahedral micro-diamonds – all 10 to 700 micron in size, many occurring in clusters,” Prof Taylor said.

Scientists believe that diamonds form at some 160 km deep in the Earth’s mantle and are carried to the surface by special volcanic eruptions. However, most mantle rocks crumble during this journey.

The rock from the Udachnaya mine is one of only a few hundred recovered in which the diamonds are still in their original setting from within the Earth.

“Diamonds never nucleate so homogeneously as this,” Prof Taylor said.

“Normally, they do so in only a few selective places and grow larger. It’s like they didn’t have time to coalesce into larger crystals.”

In addition to diamonds, the 10.5 g rock contains specks of red and green garnet and other minerals.

Prof Taylor and his colleagues examined it using a giant X-ray machine to study the diamonds and their relationships with associated materials.

They also beamed electrons at the materials inside the diamonds to study the chemicals trapped inside.

This created 2D and 3D images which revealed a relationship between minerals.

Analyses of nitrogen indicated the diamonds were formed at higher-than-normal temperatures over longer-than-normal times.

The images also showed abnormal carbon isotopes for this type of rock, indicating it was originally formed as part of the crust of the Earth, withdrawn by tectonic shifts and transformed into the shimmery rock scientists see today.

“These are all new and exciting results, demonstrating evidences for the birth mechanism of diamonds in this rock and diamonds in general,” said Prof Taylor.

The findings were presented December 15 at the American Geophysical Union’s Annual Conference in San Francisco.

The above story is based on materials provided by  American Geophysical Union’s Annual Conference.  Note: Materials may be edited for content and length.

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