30% P₂O₅. This occurs through washing, screening, deliming, magnetic separation or flotation. By comparison, the average phosphorus content of sedimentary rocks is less than 0.2%.

The phosphate is present as fluorapatite Ca₅(PO₄)₃F typically in cryptocrystalline masses (grain sizes < 1 um) referred to as collophane-sedimentary apatite deposits of uncertain origin. It is also present as hydroxyapatite Ca₅(PO₄)₃OH or Ca₁₀(PO₄)₆(OH)₂, which is often dissolved from vertebrate bones and teeth. In contrast, fluorapatite can originate from hydrothermal veins. Other sources also include chemically dissolved phosphate minerals from igneous and metamorphic rocks. Phosphorite deposits often occur in extensive layers, which cumulatively cover tens of thousands of square kilometres of the Earth's crust.