Here's a breakdown of the term:
* Intrusive: This refers to the way the rock forms. It's "intruded" into existing rock layers, rather than erupting onto the surface.
* Igneous: This means the rock formed from the cooling and solidification of molten material.
Key Characteristics of Intrusive Igneous Rocks:
* Slow Cooling: Magma cools slowly underground, allowing crystals to grow larger. This results in a coarse-grained texture, meaning the individual mineral grains are easily visible.
* Large Crystal Size: The slow cooling process gives the minerals ample time to form large crystals.
* Examples: Granite, gabbro, diorite.
Contrast with Extrusive Igneous Rocks:
Extrusive igneous rocks form when lava (magma that reaches the Earth's surface) cools and solidifies. This process happens much faster, leading to smaller crystals and a fine-grained texture. Examples include basalt, rhyolite, and obsidian.
In summary, the term "intrusive igneous rock" describes a rock that formed from magma that cooled and solidified underground, resulting in a coarse-grained texture with large crystals.
