geochemistry
Ge`o*chem"is*try (je`o*kem"is*try), n. [Gr. ge`a, gh^, the earth + chemistry.] Defn: The study of the chemical composition of, and of actual or possible chemical changes in, the crust of the earth. -- Ge`o*chem"ic*al (#), a. --Ge`o*chem"ist (#), n.