Phosphate rock is obtained from geological deposits. Its primary constituent is apatite, a calcium phosphate mineral. There are different sources of phosphate rock. The most common one is sedimentary marine deposits while the other is igneous deposits. Phosphate rock is the basis material for almost all phosphate fertilizers, either as such or transformed into phosphoric acid. Phosphate rock from sedimentary origin contains lower phosphate than phosphate rock from igneous origin (29% vs. 36%). However, it has a soft structure which confers a high reactivity to the contrary of phosphate rock from igneous origin whose structure is much harder. When added to the soil, phosphate rock slowly dissolves and gradually releases its nutrients. This happens only in slightly acidic soils and if the rock is soft enough. This product is usually used to recharge the pool of phosphorus in soils.