Key Terms & Concepts — UPSC Mains
Ringwoodite
"A high-pressure mineral in Earth's mantle transition zone capable of storing vast quantities of water as hydroxyl groups"
Ringwoodite is a high-pressure polymorph (structural variant) of olivine with the chemical formula (Mg,Fe)2SiO4. It belongs to the spinel crystal structure group and forms at depths of 525-660 km in Earth's mantle transition zone, under pressures of 18-23 GPa and temperatures above 1,600 degrees C. Ringwoodite's remarkable property is its ability to incorporate water as hydroxyl (OH-) defects within its crystal lattice — storing up to 2.6 wt% H2O. A 2014 study by Schmandt and Jacobsen (published in Science) demonstrated that the mantle transition zone contains water equivalent to approximately three times all surface oceans, stored primarily in ringwoodite and wadsleyite. The first terrestrial ringwoodite sample was found in a diamond from Juina, Brazil (Pearson et al., Nature, March 2014).
Important for UPSC GS-1 (Physical Geography — Interior of the Earth) and Prelims. UPSC tests Earth's internal structure, mineral composition at different depths, seismic discontinuities, and the origin of Earth's water. Ringwoodite connects to plate tectonics, the deep water cycle, and the debate between cometary delivery vs. internal outgassing theories of water origin.
- 1 High-pressure polymorph of olivine; forms at 525-660 km depth (mantle transition zone)
- 2 Can store up to 2.6 wt% water as hydroxyl (OH-) groups in its crystal lattice
- 3 Transition zone water reservoir estimated at three times all surface oceans
- 4 First terrestrial sample found in a diamond from Juina, Brazil (Pearson, 2014)
- 5 Transforms to bridgmanite + periclase below 660 km, releasing water via dehydration melting
The 2014 Schmandt-Jacobsen study used 2,000 USArray seismographs to demonstrate that seismic waves slow in the transition zone due to hydrous ringwoodite — proving Earth's mantle holds a water reservoir three times larger than all surface oceans.
