[ naissance diamants ]

Diamonds are forever... diverse diamond birth

found at  McGill University March 30, 2007 . En Français : Naissance diamants

Emilie Thomassot, a member of McGill’s Department of Earth and Planetary Sciences, studied nearly 60 diamonds extracted from one fist-sized sample of Earth’s mantle found in a South African diamond mine.

Her findings are highlighted as an Editor’s Choice in the March 2007 issue of Science magazine.

This unique sample originated at a depth of about 160 km and breached the surface during an explosive volcanic eruption more than one billion years ago. Thomassot measured nitrogen content and carbon and nitrogen isotopes in the diamonds, which ranged up to nearly 0.2 carats in size.

“This is the first time that anyone has observed such large chemical variation in diamonds extracted from a single sample,” said Thomassot. “The observation was completely unexpected and really turns conventional interpretations of how diamonds form on their head.”

The counterintuitive implication of the study is that gem diamonds may form from methane-bearing fluids circulating locally within the deep Earth, rather than through geodynamically induced mixing of different global carbon reservoirs. Although the existence of a methane-rich diamond-forming fluid has been predicted theoretically, direct evidence had been lacking up until now

On the Web: Science Magazine March 2007 Volume 315, Number 5819, Issue of 23 March 2007 ©2007 by The American Association for the Advancement of Science.

GEOLOGY: Diamond Diversity