State and explain what are intrusive and extrusive rocks and what is the difference between them.

Extrusive rocks are formed on the surface of the Earth from lava, which is magma that has emerged from underground e.g. Basalt. Intrusive rocks are formed from magma that cools and solidifies within the crust of the planet e.g. Granite. Extrusive rocks usually have small crystal as they cool very fast, while intrusive rocks cool very slowly leading to large crystals.