Extrusive rocks are sometimes referred to as volcanic rocks because they are formed from the cooling and solidification of lava erupted onto the Earth's surface.

Here's why this connection exists:

* Volcanoes are the primary source of lava: Volcanic eruptions bring molten rock (magma) from the Earth's interior to the surface, where it becomes lava.

* Lava solidifies to form extrusive rocks: As lava cools and solidifies, it forms igneous rocks. Since these rocks are formed from lava that originated from a volcano, they are called extrusive.

* Volcanic features: The cooling and solidification of lava often creates characteristic volcanic features like lava flows, volcanic domes, and ash deposits. These features are directly associated with extrusive rocks.

Therefore, the terms "extrusive" and "volcanic" are often used interchangeably because they describe the same process and resulting rock type.