Explain how metamorphic rocks are formed, and explain the differences between regional and contact metamorphism?

Metamorphic rocks form when pre-existing or parent rocks (whether igneous, sedimentary, or even metamorphic) are altered by heat, pressure, and the chemical activity of fluids. When the dominant altering factor is heat, usually  from direct contact , it may undergo fundamental change  in texture and recrystallization is called contact metamorphism. While regional metamorphism,  where rocks texture and minerals are changed by heat and pressure.