The Geosphere Practice Test

Igneous rocks form when molten material cools and hardens. This cooling can happen underground, producing coarse crystals, or on the surface after an eruption, yielding fine-grained or glassy textures. This distinguishes igneous rocks from metamorphic ones, which are created when existing rocks are transformed by heat and pressure, and from sedimentary rocks, which form from weathered material that’s deposited, compacted, and cemented. Magma itself is molten rock, so it isn’t yet a solid rock until it cools and solidifies.