Gneiss is a metamorphic rock that is formed from granite. Granite is a type of igneous rock that is formed from the cooling and solidification of magma or lava. When granite is subjected to high temperatures and pressure over a long period of time, it undergoes a metamorphic process and transforms into gneiss. This process involves the rearrangement of mineral crystals within the rock, resulting in the characteristic layered structure of gneiss.