Which one of the following is not an igneous rock?

Igneous rocks form from the solidification of magma or lava [1]. Granite is a common intrusive igneous rock that cools slowly underground [5]. Basalt is an extrusive or volcanic igneous rock formed from the rapid cooling of lava on the Earth's surface [4]. Pumice is also classified as an extrusive igneous rock, characterized by its porous texture and volcanic origin. In contrast, Gneiss is a metamorphic rock [2]. It is formed when a parent rock, such as the igneous rock granite, is subjected to intense heat and pressure, causing its minerals to recrystallize and often arrange into bands or layers [5]. Therefore, while granite, basalt, and pumice are igneous, gneiss is the result of metamorphism and does not belong to the igneous category.

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 13: Types of Rocks & Rock Cycle > 13.1. Igneous Rocks or Primary rocks > p. 169
2. [5] https://education.nationalgeographic.org/resource/metamorphic-rocks/
3. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 13: Types of Rocks & Rock Cycle > Extrusive Igneous Rocks (Lava Or Volcanic Rocks) > p. 170
4. [4] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 2: The Earth's Crust > Chapter 2 The Earth's Crust > p. 18
5. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 13: Types of Rocks & Rock Cycle > Some Examples of Metamorphosis > p. 174