Extrusive igneous rocks, also known as volcanic rocks, are formed at the crust's surface as a result of the partial melting of rocks within the mantle and crust.Extrusive igneous rocks cool and solidify quicker than intrusive igneous rocks.
Radiometric dating applied metamorphic rocks
Fine volcanic ash is also erupted and forms ash tuff deposits, which can often cover vast areas.
Because lava usually cools and crystallizes rapidly, it is usually fine-grained.
Hence such rocks are smooth, crystalline and fine-grained.
Basalt is a common extrusive igneous rock and forms lava flows, lava sheets and lava plateaus.
Intrusive igneous rocks are formed from magma that cools and solidifies within the crust of a planet, surrounded by pre-existing rock (called country rock); the magma cools slowly and, as a result, these rocks are coarse-grained.