Constraining the spin state of Fe in Earth’s lower mantle is critical to understanding the chemistry and dynamics of Earth’s interior. In the October 2015 issue of American Mineralogist, Dorfman et al. present an experimental study of the effect of iron concentration on the spin transition in bridgmanite. Their experiments involved two different bridgmanite compositions (38 and 74% FeSiO3). Based on the total spin moment determined by synchrotron-based X-ray emission spectroscopy, they show that Fe2+ in bridgmanite is in the high-spin state in the lower mantle but transition pressure decreases within highly enriched iron concentrations.