Here's why:

* Igneous rocks are formed from the cooling and solidification of molten rock.

* Lava is molten rock that has erupted onto the Earth's surface.

* Magma is molten rock that is still underground.

So, when lava cools and hardens, it becomes an igneous rock.

There are two main types of igneous rocks formed from volcanic activity:

* Extrusive igneous rocks: These form when lava cools and solidifies on the Earth's surface. They tend to have a fine-grained texture because the lava cools quickly. Examples include basalt, rhyolite, and obsidian.

* Intrusive igneous rocks: These form when magma cools and solidifies beneath the Earth's surface. They tend to have a coarse-grained texture because the magma cools slowly. Examples include granite and diorite.