Why do intrusive igneous rocks usually have large visible crystals?

Intrusive igneous rocks, which form from magma that solidifies deep within the Earth's crust, typically have large, visible crystals because of the slow cooling process. The high temperatures and pressures beneath the surface allow minerals ample time to grow to a size that can be seen without magnification, a texture known as phaneritic. This slow crystallization is in contrast to extrusive igneous rocks, which cool rapidly at the surface, resulting in smaller or even glassy textures.1234