Ringwoodite is a high-pressure phase of Mg2SiO4 (magnesium silicate) formed at high temperatures and pressures of the Earth's mantle between 525 and 660 km (326 and 410 mi) depth.

[6][7] This mineral was first identified in the Tenham meteorite in 1969,[8] and is inferred to be present in large quantities in the Earth's mantle.

Ringwoodite was named after the Australian earth scientist Ted Ringwood (1930–1993), who studied polymorphic phase transitions in the common mantle minerals olivine and pyroxene at pressures equivalent to depths as great as about 600 km.

Ringwoodite is thought to be the most abundant mineral phase in the lower part of Earth's transition zone.

The latter, the iron-rich endmember of the γ-olivine solid solution series, γ-Fe2SiO4, was named ahrensite in honor of US mineral physicist Thomas J. Ahrens (1936–2010).

[10] In meteorites, ringwoodite occurs in the veinlets of quenched shock-melt cutting the matrix and replacing olivine probably produced during shock metamorphism.

The 520-km depth discontinuity is generally believed to be caused by the transition of the olivine polymorph wadsleyite (beta-phase) to ringwoodite (gamma-phase), while the 660-km depth discontinuity by the phase transformation of ringwoodite (gamma-phase) to a silicate perovskite plus magnesiowüstite.

[16] An "ultradeep" diamond (one that has risen from a great depth) found in Juína in western Brazil contained an inclusion of ringwoodite — at the time the only known sample of natural terrestrial origin — thus providing evidence of significant amounts of water as hydroxide in the Earth's mantle.

[7] For experiments, hydrous ringwoodite has been synthesized by mixing powders of forsterite (Mg2SiO4), brucite (Mg(OH)2), and silica (SiO2) so as to give the desired final elemental composition.

The ringwoodite aggregates can show every shade of blue, purple, grey and green, or have no colour at all.