Strip mine spoils derived from overburden rocks of the Pennsylvanian Wise Formation in Buchanan County, Virginia, commonly contain 40% less than 2 mm sized soil material. The physical and chemical properties of these soil materials are related to their rock origin. The soil materials are alkaline due to the presence of carbonates. The principal source of P in the soil material is apatite, and the principal source of K is mica. A greenhouse experiment was conducted in order to identify the effects of biological weathering on soil material properties. Black locust (Robinia pseudoacacia L.) and sericea lespedeza (Lespedeza cuneata Dumont) were grown on unfertilized calcareous goethitic sandstone rock and soil material for one year. Soil material pH was uniformly reduced by plant action regardless of proximity to roots. The P present in the soil material, however, was not uniformly depleted. Over half of the P removed from the soil material by black locust and sericea lespedeza was P which cannot be extracted using dilute HCl-H2SO4, but can be extracted using concentrated HCl.Considerable nonexchangeable K was removed from the soil material by both plant species. X-ray diffraction was used to evaluate the effect of K removal on mica weathering. The 14 Å/ 10 Å peak area ratio was determined for both 2-0.2 µm clay and <0.2 µm clay, and black locust was found to have weathered 2-0.2 µm mica to vermiculite. The results of this experiment indicate that black locust, sericea lespedeza, and associated microorganisms, can cause biological weathering. Acidification of the soil material increases the availability of P present in apatite particles. Uptake of K insures that the soil solution is constantly replenished with K from mica and that mica is transformed into vermiculite.