1837, from metamorphic + -ism.
metamorphism (mět'ə-môr'fĭz'əm) The process by which rocks are changed in composition, texture, or structure by extreme heat and pressure. ◇ In prograde metamorphism metamorphic rocks that were formed under low pressure and temperature conditions undergo a second metamorphic event in which they are exposed to higher pressures and temperatures. ◇ In retrograde metamorphism metamorphic rocks that were formed under high pressure and temperature conditions undergo a second metamorphic event in which they are exposed to lower pressures and temperatures. See more at contact metamorphism, regional metamorphism. |