Wadsleyite

Wadsleyite is a high-pressure polymorph of olivine, with the chemical formula Mg2SiO4, and is the beta phase of magnesium silicate. It adopts a spinel-like crystal structure and forms under the extreme pressures found in Earth's mantle.

In the mantle transition zone, roughly between 410 and 520 kilometers in depth, olivine transforms into wadsleyite. This corresponds to pressures around 12–18 gigapascals and elevated temperatures characteristic of that region. Wadsleyite is stable at these conditions and, with further depth and temperature increases, it converts to ringwoodite and eventually to other mantle minerals.

Wadsleyite has a relatively high density and is a key phase for understanding seismic discontinuities, particularly the boundary observed near 410 kilometers depth. Its crystal structure allows for the incorporation of hydroxyl groups, which has led to discussions that wadsleyite and related phases could store water in the mantle transition zone. Laboratory experiments using diamond anvil cells and shock compression have characterized its properties, and seismic data interpreted to reflect a 410-km discontinuity are compatible with the olivine-to-wadsleyite transition. Wadsleyite is part of the broader olivine family of high-pressure polymorphs that record conditions in Earth's interior.