Which rock type is defined by cooling and solidification of molten material?

• A. Sedimentary
• B. Metamorphic
• C. Igneous
• D. Clastic

Answer: (C)

Rocks are classified by how they form, and igneous rocks come from cooling and solidification of molten material. This molten material, produced by melting existing rocks, crystallizes either underground as magma or on the surface as lava. The cooling rate shapes the texture: slow cooling allows crystals to grow large, giving coarse-grained rocks like granite, while rapid cooling produces small crystals or a glassy texture, as in obsidian.

Sedimentary rocks form from the deposition and lithification of sediments, not from molten material. Clastic is a type of sedimentary rock made of broken fragments. Metamorphic rocks arise from existing rocks transformed by heat and pressure, not from cooling magma. So the process described—cooling and solidification of molten material—defines igneous rocks.