Igneous rocks form primarily by which process?

• A. Sedimentation to form igneous rocks
• B. Magma crystallizes to form igneous rocks
• C. Weathering forms igneous rocks
• D. Metamorphism forms igneous rocks

Answer: (B)

Igneous rocks come from molten material that cools and solidifies. This happens when magma crystallizes as it loses heat, either underground to form coarse, intrusive rocks or after eruption at the surface to create fine-grained or glassy rocks. Because these rocks originate from molten rock, the key process is the crystallization of magma. Sedimentation, weathering, and metamorphism involve other pathways: sedimentation builds sedimentary rocks from particles, weathering breaks down rocks, and metamorphism reshapes existing rocks under heat and pressure.