Metasomatism is the chemical alteration of a rock by hydrothermal and other fluids. Synonyms to the word metasomatism are metasomatose and metasomatic process. The word metasomatose can also be used as a name for specific varieties of metasomatism (for example Mg-metasomatose and Na-metasomatose). Metasomatism can occur via the action of hydrothermal fluids from an igneous or metamorphic source.