Eolian sands tend to be fine grained and quartz rich. This mineralogical maturation may be attributed to mechanical breakdown of sand-size feldspar grains and their subsequent winnowing from dune fields. During eolian transport, ballistic impacts between saltating grains and stationary grains on the ground are very common. If the impact is sufficiently strong, the collision may be inelastic and part of the kinetic energy of the incident grain may be dissipated through inelastic deformation and subsequent breakdown of the grains involved in the collision. The theoretical calculation presented in this chapter indicate that the mechanical breakdown of feldspar sand grains through ballistic impact can be achieved if wind speed exceeds 10 m·s⁻¹. Therefore, quartz-rich sand can result from ballistic impacts between sand grains in deserts.