* Extrusive Igneous Rocks: These rocks form when magma (molten rock) erupts onto the Earth's surface as lava and cools quickly. The rapid cooling process leads to the formation of small crystals, resulting in fine-grained textures. Some common examples include:
* Basalt: A dark-colored, fine-grained rock often found in oceanic crust and shield volcanoes.
* Andesite: An intermediate-colored, fine-grained rock found in stratovolcanoes.
* Rhyolite: A light-colored, fine-grained rock found in explosive volcanoes.
* Obsidian: A volcanic glass formed when lava cools too quickly for crystals to form.
* Pumice: A porous rock formed when lava containing gas bubbles cools quickly.
* Intrusive Igneous Rocks: While not directly formed by eruptions, these rocks are formed when magma cools slowly beneath the Earth's surface. The slow cooling process allows larger crystals to form, resulting in coarse-grained textures. Examples include:
* Granite: A light-colored, coarse-grained rock often found in batholiths (large underground intrusions).
* Gabbro: A dark-colored, coarse-grained rock often found in the oceanic crust.
The type of rock formed by a volcano depends on the composition of the magma, the rate of cooling, and the presence of gases.
