The phosphatic concretions are relatively concentrated in the siliceous clay rocks. They mainly spreaded in the western part of Hunan, cental part of Guizhou and southeastern part of Sichuan. As to geological times, they belong to the Sinian Doushantou age and Early Cambrian, respectively.The phosphatic concretion is composed of several different minerals: mainly apatite and quantz, and small amount of calsite, illite, pyrite, limonite and orgenic carbon, etc. The striking characteristics of the phosphatic concretion are the broad variation of P2O5 content (from 0.50% to 32.85%). Some concretions containing the lowest P2O5 percentage (0.50%) are at the same time richest in SiO2(95.58%). This may arise from sillfication during diagenesis.The phosphatic concretions are mainly conposed of phosphatic clots, algal clasts and fibrous apatite. They formed the special pectination. The clots and algal jlasts in concretion were deposited on the sea-floor together with silica and clay in adjoining rock at the same time. The fibrous apatite was precipitated from pore water during diagenesis. The phosphatic concretions may be formed due to continuous precipitation and growth of the fibrous apatite in an alkaline microenvironment.