Extrusive Igneous Rocks:
* Form: They form when magma (molten rock) erupts onto the Earth's surface as lava, then cools and solidifies relatively quickly.
* Characteristics:
* Fine-grained texture (small crystals) due to rapid cooling.
* Often contain holes (vesicles) from escaping gases.
* Examples: basalt, rhyolite, obsidian, pumice.
Intrusive Igneous Rocks:
* Form: They form when magma cools and solidifies beneath the Earth's surface.
* Characteristics:
* Coarse-grained texture (large crystals) due to slow cooling.
* Often have a more uniform appearance.
* Examples: granite, gabbro, diorite, peridotite.
Here's a table summarizing the key differences:
| Feature | Extrusive Igneous Rocks | Intrusive Igneous Rocks |
|---|---|---|
| Formation | Magma erupts as lava and cools on the surface | Magma cools and solidifies beneath the surface |
| Cooling Rate | Fast | Slow |
| Crystal Size | Fine-grained (small crystals) | Coarse-grained (large crystals) |
| Texture | Often vesicular (contains holes) | Uniform |
| Examples | Basalt, rhyolite, obsidian, pumice | Granite, gabbro, diorite, peridotite |
In addition to these primary categories, igneous rocks can also be classified based on their mineral composition. This classification system further helps us understand the origin and characteristics of these rocks.
