ASBOG Practice Exam 2025 – 400 Free Practice Questions to Pass the Exam

The formation of igneous rock is directly associated with the cooling and solidification of magma, whether that occurs beneath the Earth's surface (intrusive igneous rock) or on the surface following a volcanic eruption (extrusive igneous rock). As magma rises through the Earth's crust and either cools slowly underground, it forms large crystals characteristic of intrusive rocks. When magma erupts as lava and cools quickly, it forms fine-grained structures typical of extrusive rocks. This solidification process is fundamental to the rock cycle and distinguishes igneous rocks from other types.

In contrast, metamorphic rocks arise from the transformation of existing rock types (igneous, sedimentary, or other metamorphic rocks) under heat and pressure without melting. Sedimentary rocks form from the accumulation and compaction of sediments, which can originate from the erosion of existing rocks, biological activity, or chemical processes. Organic rock, such as coal, specifically results from the accumulation of plant material, emphasizing biological processes rather than the physical processes that define how igneous rocks form. Therefore, the characteristics that define igneous rocks clearly position them as the type of rock formed from magma.