has part adjacent to piece of rock soil dust planetary crust regolith A solid layer which is composed primarily of loose, heterogeneous, superficial material covering solid rock. Regolith typically includes dust, soil, broken rock, and similar materials, but can be highly variable. The various parts of the regolith are highly variable. Perhaps some sort of "unconsolidated" quality should be used here with "environmental material" to cover this scope. Note that organisms, their parts, or their derivatives are also included. solid layer