High-pressure in situ x-ray diffraction and transmission electron microscopy on quenched samples show that natural garnet transforms to orthorhombic perovskite (and minor coexisting phases) containing increasing amounts of aluminum with increasing pressure. This suggests that the perovskite is the dominant host mineral for aluminum in Earth’s lower mantle. Orthorhombic perovskite is quenched from similar to 35 gigapascals but, because of the increased aluminum content, transforms to the LiNbO3 structure upon quenching from similar to 60 gigapascals.