Many models of the strength of Earth's crust and mantle are derived from studies on monomineralic isotropic rocks that deform homogeneously; however, the vast majority of rocks contain multiple phases with different strengths and pre-existing features such as pores, cracks, lattice preferred orientations and foliations/bedding. These heterogeneities cause rock strengths to deviate from simplistic models of crust and mantle strength and initiate the processes that control earthquake nucleation and ductile strain localization. We celebrate these deviations from homogeneity and invite studies of the effects of atom to formation-scale heterogeneities on the rheology of the crust and mantle from field, theory and experimental investigators of rheology to contribute to this session. Our aim is to provide an in-person(!), in-depth look at the state-of-the-art of investigating the processes caused by heterogeneities in various fields and systems to identify promising paths forward that will improve rheological models of the lithosphere.

• MR - Mineral and Rock Physics