Xenolith digestion during sinking in a corrosive magma is treated with a surface-controlled dissolution relation suggested from recent experiments on silicate crystals. The relation is shown to apply to a wide range of dynamical regimes from analog experiments on NaCl dissolution in water. Using this relation, xenolith penetration by sinking into magmas is shown to be strongly dependent on xenolith size. Crystal sinking is unimportant but sinking of meter-sized chunks can be a major proces of mass and heat transport in planetary-scale magma body evolution. This evolution cannot be adequately treated with current information.