ASBOG Practice Exam 2025 – Comprehensive All-in-One Guide to Ace Your Geology Licensure!

Igneous rocks are defined as those that form through the cooling and solidification of magma or lava. This process can occur either beneath the Earth’s surface, where the magma cools slowly and crystallizes to form intrusive (or plutonic) igneous rocks, such as granite, or at the Earth's surface, where lava cools quickly to create extrusive (or volcanic) igneous rocks, such as basalt. The composition and texture of igneous rocks largely depend on their cooling history and the minerals present in the original magma.

The other definitions represent different rock types. Rocks formed by chemical precipitation typically refer to sedimentary rocks, which form when mineral-rich water evaporates and leaves behind solids. Compacted sediments also describe sedimentary rocks, where material accumulates and solidifies over time. Lastly, rocks that contain biological materials generally pertain to organic-rich sedimentary rocks, which are formed from accumulated plant and animal materials. Therefore, the distinguishing characteristic of igneous rocks is their origin from molten material, setting them apart from these other categories of rocks.