Intrusive Igneous Rocks:
* Form underground: Magma, molten rock beneath the Earth's surface, cools and crystallizes slowly within the Earth's crust.
* Large crystals: The slow cooling process allows for larger crystals to form, giving intrusive rocks a coarse-grained texture (e.g., granite).
* Examples: Granite, gabbro, diorite
Extrusive Igneous Rocks:
* Form above ground: Lava, molten rock that erupts onto the Earth's surface, cools and solidifies quickly.
* Small crystals: Rapid cooling doesn't allow for large crystals to form, resulting in a fine-grained texture (e.g., basalt). Sometimes, the cooling is so fast that no crystals form, creating a glassy texture (e.g., obsidian).
* Examples: Basalt, rhyolite, pumice
Here's a table summarizing the differences:
| Feature | Intrusive Igneous Rocks | Extrusive Igneous Rocks |
|-----------------|-------------------------|--------------------------|
| Formation | Underground | Above ground |
| Cooling Rate | Slow | Fast |
| Crystal Size | Large | Small or none |
| Texture | Coarse-grained | Fine-grained, glassy |
In addition to the above, here are some other important points to remember:
* Cooling rate directly affects crystal size: The slower the cooling, the larger the crystals.
* Intrusive rocks are often associated with mountains and volcanic activity: Magma rising through the crust can create large underground bodies of intrusive rock.
* Extrusive rocks are often found on the surface of the Earth: They form from volcanic eruptions and can be found in a variety of settings, such as lava flows, volcanic domes, and ash deposits.
Understanding the difference between intrusive and extrusive igneous rocks is essential for understanding the processes that form different types of rocks and the evolution of the Earth's crust.
