Which term best describes a rock formed from molten material that has cooled and solidified beneath the surface or after eruption?

• A. Igneous Rock
• B. Metamorphic Rock
• C. Sedimentary Rock
• D. Mineral

Answer: (A)

Molten material from inside the Earth that cools and crystallizes, either beneath the surface (intrusive) or after erupting onto the surface (extrusive), defines igneous rocks. As the melt loses heat, minerals crystallize and interlock to create a solid rock, with textures ranging from coarse-grained granite to glassy obsidian depending on cooling rate and composition. This distinguishes igneous rocks from metamorphic rocks, which form when existing rocks are altered by heat and pressure, and sedimentary rocks, which form from deposited and lithified sediments. A mineral, meanwhile, is a single substance, not a rock. So the term described is igneous rock.