Which statement describes igneous rocks that form at or near Earth's surface?

Which statement describes igneous rocks that form at or near Earth's surface?

• A. Igneous rocks formed deep underground
• B. Sedimentary rocks formed from sediments
• C. Metamorphic rocks formed under pressure
• D. Igneous rocks formed at or near Earth's surface

Answer: (D)

Igneous rocks form when molten rock cools and solidifies, and where that cooling happens changes the texture and type. If cooling occurs at or near the surface, it happens quickly, so crystals are very small or the rock becomes glassy. Those rocks form at or near Earth’s surface and are known as extrusive (volcanic) igneous rocks. This is different from rocks that cool slowly underground, which become coarse-grained intrusive igneous rocks. Sedimentary rocks come from sediments that are deposited and compacted, and metamorphic rocks form when existing rocks are altered by heat and pressure. So describing igneous rocks that form at or near Earth’s surface correctly points to the surface-fast cooling, i.e., extrusive igneous rocks.

Igneous rocks form when molten rock cools and solidifies, and where that cooling happens changes the texture and type. If cooling occurs at or near the surface, it happens quickly, so crystals are very small or the rock becomes glassy. Those rocks form at or near Earth’s surface and are known as extrusive (volcanic) igneous rocks. This is different from rocks that cool slowly underground, which become coarse-grained intrusive igneous rocks. Sedimentary rocks come from sediments that are deposited and compacted, and metamorphic rocks form when existing rocks are altered by heat and pressure. So describing igneous rocks that form at or near Earth’s surface correctly points to the surface-fast cooling, i.e., extrusive igneous rocks.