What are three methods of intrusive igneous rock fromation?

Intrusive igneous rock formation primarily occurs through three methods: magma cooling and solidification beneath the Earth's surface, leading to the formation of plutonic rocks like granite; magma injection into existing rock layers, forming dikes and sills; and the accumulation of magma in large chambers, which can crystallize over time to create batholiths. These processes allow for the slow cooling of magma, resulting in the formation of coarse-grained textures in the resulting rocks.