Water Rich Gem ‘Ringwoodite’ Offers Clues to Vast Oceans Beneath the Earth’s Mantle

A sample of a rare water-rich gem called 'ringwoodite' offers new clues about the presence of a large volume of water beneath the Earth's mantle.

An international team of scientists from the University of Alberta, uncovered the first terrestrial sample of a water-rich mineral that supports scientific theories about the large volume of water held 410-660 kilometers beneath the Earth's surface i.e. between the upper and lower mantle. Analysis of the Ringwoodite revealed that it was 1.5 percent water.

"This sample really provides extremely strong confirmation that there are local wet spots deep in the Earth in this area. That particular zone in the Earth, the transition zone, might have as much water as all the world's oceans put together," said Graham Pearson, Canada Excellence Research Chair in Arctic Resources at the U of A, who discovered the mineral.

Believed to exist in large quantities in the transition zone under high pressure, Ringwoodites have earlier been found in meteorites. It is a form of the mineral peridot and terrestrial samples are almost non-existent, mainly due to the lack of field work conducted at such great depths.

The terrestrial sample was found in the year 2008 near Juina area of Mato Grosso, Brazil.  The sample was among a host of diamonds miners unearthed from the river gravels. The diamond came from the depths in a fragment of volcanic rock called Kimberlite.

The team got lucky on this accidental discovery they made from the 3 millimeter wide brown diamond. The water rich gem is extremely tiny and is invisible to te naked eye.

"It's so small, this inclusion, it's extremely difficult to find, never mind work on," Pearson said, "so it was a bit of a piece of luck, this discovery, as are many scientific discoveries."

The researchers spent years examining the mineral and exposing it to an array of analysis that included Raman and infrared spectroscopy and X-ray diffraction.  After all this they confirmed that the mineral was indeed the first terrestrial sample of a water-rich ringwoodite'.

"One of the reasons the Earth is such a dynamic planet is the presence of some water in its interior," Pearson said. "Water changes everything about the way a planet works."

The study was documented in the journal Nature.