**7.2.3. Phosphorite weathering derivates**

Weathering (**Section 7.3.2**) leads to the formation of enriched residual and replacing depos‐ its from phosphatic deposits not otherwise minable. The Tennessee "brown rock" phosphate deposits consist of nowadays residuum developed through the decomposition of phosphatic limestones of Ordovician age. The "river pebble" deposits prominent in early history of phosphate mining in Florida and South Carolina are mostly placers formed by alluvial concentration of phosphatic pebbles eroded from the phosphatic formations of adjacent terrain [27].

The Tennessee "white rock" and Florida "hard rock" deposits were formed by the redeposi‐ tion of phosphate derived from the decomposition of apatite under more advanced weather‐ ing. The same decomposition-phosphatization process accounts for the formation of calcium aluminum phosphate and aluminum phosphate in the "leached zone" of the Bone Valley field and deeply weathered Cretaceous and Eocene deposits of west Africa [27].
