Dear Editor,rnPhosphorus(P)is essential and often a limiting nutrient for biological production on land and in the seas(Elser et al.,2007).The biologically available P to terrestrial and aquatic ecosystems ultimately derives from the continental weathering of rocks on the surface of the earth(Follmi,1996;Ruttenberg,2003).Rocks are usually classified into three groups based on their origins:igneous,metamorphic,and sedimentary rocks.Although tectonic activity continually cycles the three rocks into each other,igneous rocks are the primary source rocks because they are formed via cooling and hardening of lava from the mantle and are a dominant rock pool,accounting for 65％of the mass,in the crust.Both sedimentary and metamorphic rocks are considered as secondary rocks.Sedimentary rocks are formed via ac-cumulation of sediments derived from the weathering of pre-existing rocks and erosion of surface soils and often contain organic material of biological origin.Metamorphic rocks are formed via subduction of all rock types deep into the crust where they undergo metamorphisms under high pressure and temperature.Therefore,all the rocks currently present in the crust are believed to have first been igneous from the mantle.All the P that cycles through sedimentary rocks and biological systems must have been initially derived from continental weathering of crystalline rocks of igneous or metamorphic origin(Guidry et al.,2000;Horton,2015).