Which one among the following is not an igneous rock ?

Igneous rocks are formed from the solidification of magma or lava [1]. Granite is a common intrusive (plutonic) igneous rock that cools slowly within the Earth's crust [2]. Gabbro is also an intrusive igneous rock, characterized by its mafic composition and coarse-grained texture [2]. Basalt is an extrusive (volcanic) igneous rock formed when lava cools quickly at the Earth's surface [1]. In contrast, Gneiss is a metamorphic rock [3]. It forms when pre-existing rocks, such as granite or schist, are subjected to intense heat and pressure, causing the minerals to recrystallize and often form distinct bands [1]. Therefore, Gneiss is not an igneous rock but a product of metamorphism [3].

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. [2] 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
3. [3] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 13: Types of Rocks & Rock Cycle > Some Examples of Metamorphosis > p. 174