metamorphic rock

Metamorphism in the process where by one kind of rock (for example, sandstone) is changed by eons of massive pressure and heat into a different kind of rock (such as quartzite). Some metamorphic rocks include gneiss, marble, and schist. Through metamorphism, rocks change shape, become denser, and rearrange their mineral compositions to become something new. "Metamorphic intensity" is the measure of the pressure/temperature conditions at the time of the metamorphism.