Igneous rocks transform into metamorphic rocks through a process called metamorphism. This process involves changes in the mineral composition and texture of the rock due to exposure to high pressure, high temperature, or both. These conditions are typically found deep within the Earth’s crust or at tectonic plate boundaries.
When igneous rocks are subjected to these extreme conditions, the minerals within the rock begin to recrystallize. This means that the existing minerals may change into new minerals that are more stable under the new conditions. For example, the mineral feldspar in igneous rocks can transform into mica under high pressure and temperature.
Metamorphism does not melt the rock; instead, it alters the rock’s structure and composition while it remains in a solid state. The result is a metamorphic rock, which often has a layered or banded appearance due to the alignment of minerals during the process.
Common examples of metamorphic rocks formed from igneous rocks include gneiss, which can form from granite, and schist, which can form from basalt.