Final answer:
Extrusive igneous rocks form when lava solidifies on the Earth's surface. They have fine-grained textures and a dull appearance.
Step-by-step explanation:
Extrusive igneous rocks form when lava solidifies. Igneous rocks are formed when molten material cools and becomes solid. Magma is the molten rock inside the Earth, and when it reaches the surface through volcanoes or cracks, it is called lava. When lava cools on top of the Earth's surface, it forms extrusive igneous rock. These rocks cool quickly, resulting in fine-grained textures and a dull appearance.
As this lava cools and solidifies on the surface, it forms extrusive igneous rocks, which are typically fine grained due to the quick cooling process that does not allow large crystals to form. An example is basaltic lava, which can flow quickly and solidify into basalt, an extrusive igneous rock. On the other hand, if the magma cools slowly within the Earth, it forms intrusive igneous rocks like granite, which have larger, coarser grains due to the slower cooling process.