Volcanic/extrusive rocks form when magma does what?

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Prepare for your Introduction to Physical Geology Exam. Tackle diverse topics with multiple-choice questions and detailed explanations. Equip yourself with knowledge about Earth's physical processes and surface features. Ace your exam with confidence!

Multiple Choice

Volcanic/extrusive rocks form when magma does what?

Explanation:
Volcanic/extrusive rocks form when magma reaches Earth's surface as lava and cools rapidly. The eruption relieves pressure and allows the molten rock to spread and solidify quickly, giving rise to very small crystals or a glassy texture. This rapid surface cooling is what distinguishes extrusive rocks from those that crystallize underground, which become coarse-grained intrusive rocks like granite. The other processes listed aren’t how volcanic rocks form: metamorphism changes rocks under heat and pressure, and precipitation from water creates sedimentary or chemical rocks, not igneous ones.

Volcanic/extrusive rocks form when magma reaches Earth's surface as lava and cools rapidly. The eruption relieves pressure and allows the molten rock to spread and solidify quickly, giving rise to very small crystals or a glassy texture. This rapid surface cooling is what distinguishes extrusive rocks from those that crystallize underground, which become coarse-grained intrusive rocks like granite. The other processes listed aren’t how volcanic rocks form: metamorphism changes rocks under heat and pressure, and precipitation from water creates sedimentary or chemical rocks, not igneous ones.

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