1. Intrusive Igneous Rocks:
* Cool slowly underground: Magma cools and solidifies slowly beneath the Earth's surface. This slow cooling allows for the formation of large crystals.
* Characteristics: Coarse-grained texture, visible crystals (phaneritic).
* Examples: Granite, Gabbro, Diorite, Peridotite
2. Extrusive Igneous Rocks:
* Cool rapidly on the surface: Magma erupts onto the Earth's surface as lava, which cools and solidifies quickly. This rapid cooling results in small crystals.
* Characteristics: Fine-grained texture, small crystals or no visible crystals (aphanitic), sometimes with holes from escaping gas (vesicular).
* Examples: Basalt, Rhyolite, Andesite, Obsidian, Pumice
Here's a table summarizing the key differences:
| Characteristic | Intrusive | Extrusive |
|---|---|---|
| Cooling Environment | Underground | Surface |
| Cooling Rate | Slow | Rapid |
| Crystal Size | Large | Small or None |
| Texture | Coarse-grained (phaneritic) | Fine-grained (aphanitic), Vesicular |
| Examples | Granite, Gabbro, Diorite, Peridotite | Basalt, Rhyolite, Andesite, Obsidian, Pumice |
Remember that these are just two broad categories. Within each category, there are many different types of igneous rocks with varying mineral compositions and textures.
