Gneiss is a type of rock that is characterized by its banded appearance and is composed of quartz, feldspar, and mica. It is a metamorphic rock, meaning it has been changed by extreme pressure and heat from its original form. Gneiss is often used in construction and is known for its durability and strength. It also has a unique sound when struck, which is why it is sometimes referred to as 'rock that sounds swell'.