* Slow Cooling: When magma intrudes into the Earth's crust, it's surrounded by relatively cool rock. This creates a slow cooling process.
* Crystal Growth: As magma cools, its minerals start to crystallize. Slow cooling gives the mineral crystals ample time to grow large and well-defined. This is why intrusive rocks are known for their large, visible crystals.
* Example: Granite, a common intrusive rock, is known for its large, interlocking crystals of quartz, feldspar, and mica.
Contrast with Extrusive Rocks:
Extrusive rocks, which form from lava that cools quickly on the Earth's surface, tend to be fine-grained or even glassy. This is because the rapid cooling doesn't allow for the formation of large crystals.
