nodular phosphorite

Nodular phosphorite is a type of rock characterized by a high concentration of phosphates, found in rounded or compact masses. These phosphates can originate from marine invertebrates that create shells from calcium phosphate, as well as from the bones and waste of vertebrates.12

Phosphorite deposits are often found in areas with carbonaceous shale and chert, or on stable landforms associated with sandstone or shale. These rocks typically contain about 30 percent phosphorous pentoxide (P₂O₅) and are a primary source for the world's phosphate fertilizers. Significant deposits exist in the United States, Peru, Morocco, and Western Sahara.13