Ringwoodite is the high-pressure form of the mineral olivine (Mg2SiO4) that occurs between 520 and 660 km below the surface of the earth in the transition zone. The first terrestrial observation of this mineral was in a diamond from Juina, Brazil (top left). Water content in this 30 μm inclusion (bottom left) is around 1.4 wt.%, indicating that the global transition zone could contain at least 2.5 times the amount of water as Earth’s oceans. Images of ringwoodite in a Juina diamond from Graham Pearson (University of Alberta).
Water is carried down into Earth at subduction zones by the process of plate tectonics. Much of the water escapes close behind the subduction zone, promoting melting of the mantle and giving rise to the volcanic chains in the Pacific Ocean basin known as the Ring of Fire, and many other volcanoes elsewhere.
But can water be carried even further into the mantle? How would we even know? Why is it important, and what are the effects of such deep water storage? Diamonds can give us the answers to these questions. Recent discoveries of water-containing mineral in- clusions and even free water held at high pressures in diamonds tell us that water is carried into Earth’s deep interior—perhaps as deep as 700 km.
Read more here.
To read more about Graham's groundbreaking ringwoodite discovery, go here.