*metasomatism*

n. [ Pref. meta- + Gr. &unr_;, &unr_;, body. ] (Geol.) An alteration in a mineral or rock mass when involving a chemical change of the substance, as of chrysolite to serpentine; -- opposed to ordinary metamorphism, as implying simply a recrystallization. -- Met`a*so*mat"ic a. [1913 Webster]