Gneiss is a metamorphic rock formed when intense heat and/or pressure is applied to it's parent rock schist.

Sedimentary rocks are formed from the accumulation and compression of sediments, while metamorphic rocks are formed from the alteration of existing rocks due to heat, pressure, or chemical reactions. Sedimentary rocks are typically layered and can contain fossils, while metamorphic rocks have a more crystalline structure and may exhibit foliation.