Extrusive igneous rocks are formed from lava that cools and solidifies on the Earth’s surface. This process occurs during volcanic eruptions. Some common examples of extrusive igneous rocks include:
- Basalt: This is one of the most common extrusive igneous rocks. It is dense and dark-colored, formed from the rapid cooling of low-viscosity lava.
- Pumice: A light, porous rock that forms when volcanic lava cools quickly and traps gas bubbles, giving it a frothy appearance.
- Obsidian: Known for its glassy texture and sharp edges, obsidian forms when lava cools so rapidly that crystallization does not occur.
- Rhyolite: This rock has a composition similar to granite but forms from lava that cools quickly, resulting in a fine-grained texture.
- Andesite: Found often in volcanic arcs, andesite has a composition between basalt and rhyolite and typically forms in moderate eruptive conditions.
These rocks provide insight into volcanic processes and the conditions under which they formed, helping geologists understand the Earth’s history and the dynamics of volcanic activity.