The crucial difference between igneous rock and volcanic rock lies in where they cool and solidify: volcanic rocks are a type of igneous rock that forms on the Earth's surface, while igneous rocks can form either on the surface (volcanic/extrusive) or deep underground (plutonic/intrusive).
Here's a more detailed breakdown:
Understanding Igneous Rocks
- Igneous rocks are formed from the cooling and solidification of molten rock. This molten rock is called magma when it's below the Earth's surface and lava when it erupts onto the surface.
- Igneous rocks are broadly classified based on their formation location and mineral composition.
Volcanic Rocks: A Subtype of Igneous Rock
- Volcanic rocks, also known as extrusive igneous rocks, are formed when lava cools and solidifies on the Earth's surface. This rapid cooling often results in a fine-grained texture or even a glassy texture, due to the quick crystallization of minerals.
- Examples of volcanic rocks include basalt, rhyolite, and obsidian.
Plutonic Rocks: The Other Type of Igneous Rock
- Plutonic rocks, also known as intrusive igneous rocks, are formed when magma cools and solidifies beneath the Earth's surface. This slow cooling allows for the formation of larger crystals, resulting in a coarse-grained texture.
- Examples of plutonic rocks include granite and diorite.
Here's a table summarizing the key differences:
| Feature | Igneous Rock | Volcanic Rock (Extrusive) | Plutonic Rock (Intrusive) |
|---|---|---|---|
| Formation | Cooling and solidification of molten rock | Cooling and solidification of lava on the Earth's surface | Cooling and solidification of magma beneath the surface |
| Cooling Rate | Varies | Rapid | Slow |
| Texture | Varies (can be fine-grained or coarse-grained) | Fine-grained to glassy | Coarse-grained |
| Location | Surface or beneath the surface | On the Earth's surface | Beneath the Earth's surface |
| Alternate Name | N/A | Extrusive Igneous Rock | Intrusive Igneous Rock |
| Common Examples | Granite, Basalt | Basalt, Rhyolite, Obsidian | Granite, Diorite |
In simpler terms: All volcanic rocks are igneous rocks, but not all igneous rocks are volcanic. Igneous rock is the overarching category, and volcanic rock is a specific type defined by its formation on the Earth’s surface.
