Abstract: In this paper, the relation between mineral composition of rocks and the earthquake reflecting ability of hydro-geochemical composition was discussed. From the view point of chemistry, it is revealed that a variety of chemical reaction may take place during the seism ogenic process. The purpose of this paper is to point out the inherent factor causing hydro-geochemical precursory anomaly and prov iding inherent theoretical foundation for the hydro-geochemical precursory anomaly.

Key words: Hydro-geochemistry, Earthquake-reflecting ability, Precursory index, [AIO₄] tetrahedron