However , a number of US phosphate deposits occur where the original marine - deposited phosphate minerals have been concentrated by weathering and redeposition , often under nonmarine conditions .
Most phosphate mining is of sedimentary phosphorite , a phosphorus - rich deposit formed under shallow marine conditions .
A number of US phosphate deposits occur where the original marine - deposited phosphate minerals have been concentrated by weathering and redeposition , often under nonmarine conditions .
Most phosphate mining is of sedimentary phosphorite , a phosphorus - rich deposit formed under shallow marine conditions .