metamorphism

noun

1. Geology. a change in the structure or constitution of a rock due to natural agencies, as pressure and heat, especially when the rock becomes harder and more completely crystalline.
2. Archaic. metamorphosis.

noun

1. the process by which metamorphic rocks are formed
2. a variant of metamorphosis

n.1837, from metamorphic + -ism.

1. 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.