Gneiss is a metamorphic rock formed from?

Gneiss is a type of metamorphic rock that primarily forms from the metamorphism of granite. Let's break this down to understand it better.

Metamorphic rocks are formed when existing rocks are subjected to high heat, high pressure, or chemically active fluids. This process, known as metamorphism, alters the mineral composition and structure of the original rock, also known as the parent rock or protolith.

Granite is an igneous rock composed mainly of quartz, feldspar, and mica. When granite undergoes metamorphism, typically deep within the Earth's crust where pressures and temperatures are high, it changes into a different kind of rock.

The specific conditions cause the minerals within the granite to align into bands or layers, giving gneiss its characteristic banded appearance. This banding is called "foliation."

While other types of rocks like slate, shale, and sandstone can also undergo metamorphism, they result in different metamorphic rocks. For instance:

• Slate forms from shale.
• Shale forms into slate and eventually into phyllite, schist, or gneiss under different conditions.
• Sandstone forms into quartzite.

In summary, gneiss is primarily the result of the metamorphism of granite.