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.

Chemical alteration of a rock by the action of hydrothermal fluids.

A change in the bulk chemical composition of a rock by fluid transport of some chemical components into or out of the rock.

the process by which one mineral is replaced by another