The formation of granite begins with magma generated deep in the Earth's mantle or lower crust. This magma is typically rich in silica and alkali metals, which also define granite's chemical composition. As the magma rises towards the Earth's surface, it starts cooling slowly. This gradual cooling is crucial, as it allows time for the large, identifiable crystals of quartz, feldspar, and other minerals, to form.
Granite is primarily found in two geological settings. The first is in continental crust, where it forms massive plutonic bodies known as batholiths. These batholiths are often the cores of mountains and can cover hundreds of square kilometers. The second common setting is in smaller intrusions like dikes, sills, and stocks. These are essentially offshoots of the main magma body that were injected into cracks and spaces in the surrounding rock.
As the magma cools, different minerals crystallize at different temperatures, a process known as fractional crystallization. This leads to the diverse mineral compositions found in various granites and contributes to the wide array of colors and textures that we see in granite rocks.