* Metamorphism is a process of change: Metamorphic rocks are formed when existing rocks (igneous, sedimentary, or even other metamorphic rocks) are subjected to intense heat and pressure deep within the Earth's crust.
* Conditions are key: These conditions cause the rock's mineral composition and texture to change without melting completely.
* Not all rocks withstand the heat: Some rocks, like very soft, porous sedimentary rocks, might simply be destroyed by the intense heat and pressure.
In essence, rocks that are stable enough to withstand the intense heat and pressure of metamorphism are the ones that can transform into metamorphic rocks.
For example, sandstone can become quartzite, limestone can become marble, and shale can become slate.
