noun
metamorphism
Geological term referring to the process by which rocks are changed by heat, pressure, or chemical action.
変成作用によって石灰岩が大理石に変わる。
Limestone turns into marble through metamorphism.
変成岩 is the resulting metamorphic rock, while 変成作用 is the process itself.
Compound of 変成 (metamorphosis, change) and 作用 (action, effect), used as a geological term.