Final answer:
The crystallization of igneous rocks is influenced by the cooling rate of magma or lava, with extrusive rocks cooling rapidly on the surface, leading to fine-grained textures, and intrusive rocks cooling slowly underground, leading to coarse-grained crystals like those in granite.
Step-by-step explanation:
The crystallization of igneous rocks is directly related to the rate at which the lava or magma cools. For extrusive igneous rocks, which cool quickly on the Earth's surface, the process results in fine-grained or not fully crystallized textures because there is insufficient time for large crystals to form. On the contrary, intrusive igneous rocks, such as plutonic rocks, cool slowly beneath the Earth's surface, allowing the formation of large, coarse-grained crystals. This slow cooling within the crust leads to a sugary appearance due to the interlocking of flat crystal faces reflecting light. Granite, for example, is a type of coarse-grained igneous rock formed from slow cooling magma, characterized by its prevalence of light-colored minerals. When considering the formation of igneous rocks, it's important to distinguish between plutonic and volcanic rocks because of their differing cooling ages and resulting textures. As rocks formed in different environments, they provide critical insight into geological processes and the history of Earth's crust. In a tectonic setting where both extrusive and intrusive rocks are formed simultaneously, magma that reaches the surface and cools rapidly produces fine-grained volcanic rock, while magma that remains underground and cools slowly transforms into coarse-grained plutonic rock.