Rock phosphate is a suitable fertiliser for soils which are

Phosphorite or rock phosphate is a non-detrital sedimentary rock that contains high amounts of phosphate minerals. The phosphate content of phosphorite varies from 4 - 20% phosphorous pentaoxide.
Rock phosphate is a natural source of phosphorous and is suitable fertilizer for soils that are Acidic as low pH helps to solubilize the rock phosphate and increases the available form of P to the plants.