Deposits of Industrial Rocks
1984-1-1 · Residual phosphate deposits (30 % PpOc) form by chemical weathering of weakly phosphatized carbonate rocks (see Sect,2.9, Table 8, gen.type 66). They make up a cover of karstified limestones (in Tennessee, U.S.A., called "blanket deposits" formed of "brown rock") and fill the depressions in their surface. 10.