Natural processes such as earthquakes, volcanism, and mountain building are driven by plate tectonics, which are fundamentally influenced by the deformation of rocks and minerals under various environmental conditions. Understanding the rheology of rock-forming minerals is thus crucial for deciphering the geodynamics of Earth. Our current understanding of mineral rheology is primarily derived from laboratory experiments and theoretical models based on simplified synthetic systems. However, the properties of minerals are significantly affected by structural defects and impurities, making the extrapolation to natural, chemically complex systems uncertain. Crystal defects such as dislocations, chemical impurities and vacancies play a crucial role in influencing the elastic properties of minerals and their rheology, introducing deviations from the idealized, flawless structure. These defects act as perturbations that impede the smooth transmission of mechanical forces within the crystal structure, consequently influencing its overall elasticity and, in turn, impacting the material's macroscopic mechanical properties. In addition to defects and vacancies, minerals often contain fluid, melt and solid inclusions that can reach significant volumetric abundances and strongly affect the elastic properties (and thus the mechanical properties and rheology) of the host crystal. The investigation of mineral inclusions does offer a unique opportunity to study their impact on the rheology of the host mineral in situ. This approach holds great potential for enhancing our comprehension of the rheology of mineral assemblages and, consequently, the dynamics of our planet.