Atomic structure of iron-bearing magnesium silicate perovskite, showing iron (orange) and magnesium (green) sites. High pressure triggers a crossover from high- to low-spin iron at the central (octahedral) site.

From the article:

Spin-State Crossover and Hyperfine Interactions of Ferric Iron in ${\mathrm{MgSiO}}_3$ Perovskite
Han Hsu, Peter Blaha, Matteo Cococcioni, and Renata M. Wentzcovitch
Phys. Rev. Lett. 106, 118501 (2011)

View Issue Table of Contents