Abstract: The main chemical compositions of nephrite are SiO₂, MgO and CaO, and the isomorphous replacement makes it contain a little amount of FeO, K₂O, Na₂O, Al₂O₃ and so on. By calculating crystal-chemical formulas and analyzing the relationships among the chemical compositions, It can be found that the average chemical compositions of nephrites from different localities in China are very close to theoretical value of tremolite. The result indicates that the main mineral of nephrite is tremolite. In addition, the chemical compositions can also reflect features of localities and the species to some extent. The isomorphous replacement of Fe²⁺ makes w(FeO) to be the important indicator for identifying the locality and species of nephrite.