The comminution of blocky planetary surfaces into fine-grained regoliths was simulated by impacting a fragmental gabbro target 200 times with stainless steel projecctiles (diameter=6.35 mm; mass=1.2 g; Vi=1.35 km/s). Initially the target fragments were 2--32 mm in size with a mean diameter of 15.2 mm, which was reduced to 0.4 mm after 200 shots. For the first 60 shots, comminution was linear with cumulative kinetic energy and, thus, essentially linear with time. The comminution efficiency, however, decreased at later stages. This could be due to a change in fracture mechanism from predominantly intergranular to predominantly intragranular and/or due to a change in partitioning of the projectile's kinetic energy from collisional fragmentation or large fragments at early times to cratering in a progressively finer-grained medium at later stages. Mineral-specific, preferential comminution is abundantly observed in the modal make-up of various grain-size fractions; plagioclase comminutes more rapidly than pyroxenes. Plagioclase-initially present at 54% (vol.)-comprises typically 65--70% of the 125--250 μm fraction; pyroxenes (initially at 33%) are depleted to 20--25%. This fractionation occurs in the earliest samples analyzed and is not a time-dependent phenomenon. Bulk chemical analyses reveal a corresponding increase in Al2O3, CaO, and Na2O, and a decrease in FeO and MgO. The finest grain sizes are generally the most severely affected by differential comminution. Similar, if not exactly identifical, trends are abundantly documented for lunar soil samples. These experimental findings illustrate that differential comminution is capable of producing fractionation in the finest grain sizes. They diminish the need for prominent lateral and vertical transport of components otherwise ''foreign'' to a lunar soil-sampling site as postulated by some workers on the basis of multivariate chemical mixing models.