Extrusive or volcanic rocks crystallize from lava at the earth's surface. The texture of an igneous rock (fine-grained vs coarse-grained) is dependent on the rate of cooling of the melt: slow cooling allows large crystals to form, fast cooling yields small crystals. ... They cool too quickly to form crystals.

Why are igneous rocks crystalline in nature?

The magma, which is brought to the surface through fissures or volcanic eruptions, solidifies at a faster rate. 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.

Are igneous rocks crystalline?

Igneous rocks are formed from molten rock called magma. They are mostly crystalline (made up of interlocking crystals) and usually very hard to break.