Here's why:

* Igneous refers to rocks formed from the cooling and solidification of molten rock (magma or lava).

* Crystals are solid materials with a highly ordered, repeating arrangement of atoms.

As magma or lava cools, the atoms within it begin to arrange themselves in these ordered structures, forming crystals. The size and shape of the crystals depend on factors like the rate of cooling and the composition of the magma or lava.