Phosphate Nodule

Synonym

Sedimentary phosphate deposit, Phosphorite

Required Geological Setting

Ocean floor, Lake floor

Occurrence

Phosphate-rich nodules formed on the ocean-floor or the lake-floor. Nodules contain more than 15-20 % phosphate, and deposit as amorphous material having chemical composition of carbonate-rich fluorapatite. Rocks containing phosphate-rich nodules are stratiform often associated with diatomite, and nodules are formed on cores of calcite, feldspar, fish borns, and siliceous fossils. Phosphate-rich nodules are obsreved in Cambrian to modern sediments in shallow zones of the lake-floor and the ocean-floor such as continental shelves (100 m depth), continental slopes (400 m depth), and seamounts. It is considered that nodules were formed in reductive, low dissolved oxgen, and pH 7.2-7.4 circumstances with very slow supplies of sediments. Origin of phophate is considered as phytoplankton, diatoms.

Mineral Assemblages

Carbonate-rich fluorapatite