geochemistry \ge`o*chem"is*try\ (j[=e]`[-o]*k[e^]m"[i^]s*tr[y^]), n. [Gr. ge`a, gh^, the earth + chemistry.] 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. [Webster 1913 Suppl.]