Ringwoodite
The dense, spinel-structured form of olivine, made by shock in meteorites and found deep inside Earth.
Key facts
- Formula
- (Mg,Fe)2SiO4
- Family
- High-pressure minerals
- Crystal system
- Cubic
- First described
- the Tenham L6 chondrite, 1969
Ringwoodite was first found in nature in 1969 in shock veins of the Tenham meteorite, an L6 chondrite that fell in Queensland, Australia, in 1879. It is named after Ted Ringwood, the Australian scientist who predicted that olivine would change into this form deep in Earth's mantle.
What it is
Ringwoodite has the same chemistry as olivine but its atoms are packed into a denser spinel structure. It forms from olivine at pressures of roughly 18 to 23 gigapascals, about 200,000 times the pressure of Earth's atmosphere, and high temperatures.
On Earth it is thought to make up a large part of the mantle between about 520 and 660 kilometres deep.
Where it is found
In meteorites it forms in and beside shock veins, thin dark streaks of rock melted by the shock of a collision between asteroids. It is common in strongly shocked L and H chondrites, and occurs in some Martian meteorites. Because these pressures last only seconds in an impact, the sizes of ringwoodite grains help estimate how long the shock lasted.
How it is recognised
In shock veins ringwoodite is often a striking blue or purple, unlike any olivine. It is confirmed by Raman spectroscopy or X-ray diffraction.
Did you know?
In 2014 a diamond from Brazil was found to contain a tiny ringwoodite grain holding about 1.5% water, evidence of water deep in Earth's mantle.
Ringwoodite from meteorites was studied decades before any natural sample from Earth's mantle was found.