3.6 Notes How are metamorphic rocks formed? Objective: Describe two ways in which metamorphic rocks form Metamorphic rocks form from existing rocks which are slowly changed by heat and pressure. Heat and pressure inside Earth bakes rocks and changes the minerals in them. When the minerals and chemicals inside the rock change they are called metamorphic rocks. Why are Metamorphic rocks called changed rocks? Heat: Minerals chemically change at temperatures between 200°C and 800°C. Minerals do not change chemically below 100°C. Minerals melt into magma above 800°C. Pressure: Extreme pressure, or force, can change the form of minerals and flatten minerals into layers. Heat and pressure changes rocks What can flatten minerals into layers? When rocks mix with magma, they can change into metamorphic rock. Magma can flow between layers of sedimentary rock. Heat and chemicals inside magma cause the minerals inside sedimentary rocks to change. Magma’s heat can also change minerals in igneous rocks and turn one kind of metamorphic rock into a different kind of metamorphic rock. What kinds of rocks are changed by coming into contact with magma?