Water-rich gem points to vast 'oceans' beneath Earth

In a breakthrough, scientists have found the first terrestrial sample of a water-rich gem which suggests that large volumes of water exist deep beneath the Earth.

An international team of scientists led by Graham Pearson, Canada Excellence Research Chair in Arctic Resources at the University of Alberta, has discovered the first-ever sample of a mineral called ringwoodite.

Analysis of the mineral shows it contains a significant amount of water - 1.5 per cent of its weight - a finding that confirms scientific theories about vast volumes of water trapped 410 to 660 kilometres beneath the Earth, between the upper and lower mantle.

"This sample really provides extremely strong confirmation that there are local wet spots deep in the Earth in this area," said Pearson, a professor in the Faculty of Science.

"That particular zone in the Earth, the transition zone, might have as much water as all the world's oceans put together," Pearson said.

Ringwoodite is a form of the mineral peridot, believed to exist in large quantities under high pressures in the transition zone.

Ringwoodite has been found in meteorites but, until now, no terrestrial sample has ever been unearthed because scientists have not been able to conduct fieldwork at extreme depths.

Pearson's sample was found in 2008 in the Juina area of Mato Grosso, Brazil, where artisan miners unearthed the host diamond from shallow river gravels.

The diamond had been brought to the Earth's surface by a volcanic rock known as kimberlite - the most deeply derived of all volcanic rocks.

Pearson said the discovery was almost accidental in that his team had been looking for another mineral when they found a three-millimetre-wide, dirty-looking, commercially worthless brown diamond.

The ringwoodite itself is invisible to the naked eye, buried beneath the surface, so it was fortunate that it was found by Pearson's graduate student, John McNeill, in 2009.

The sample underwent years of analysis using Raman and infrared spectroscopy and X-ray diffraction before it was officially confirmed as ringwoodite.

The study is published in the journal Nature.