Gneiss is typically formed from the metamorphism of granite or sedimentary rocks such as shale, making these the primary parent rocks.
When conditions such as heat and pressure are applied to these parent rocks over time, their minerals realign and recrystallize, leading to the formation of gneiss. The characteristic banding seen in gneiss is a result of this mineral alignment. Thus, while granite is the most common parent rock, other rocks can also undergo metamorphism to create gneiss depending on the specific conditions of the environment.”