Extrusive Rocks:
* Form from lava that erupts onto the Earth's surface. This lava cools and solidifies relatively quickly, leading to smaller crystals.
* Have a fine-grained texture (aphanitic) or a glassy texture.
* Examples:
* Basalt: A dark, dense rock commonly found in volcanic flows.
* Rhyolite: A light-colored, often glassy rock with high silica content.
* Obsidian: A volcanic glass formed when lava cools rapidly.
Intrusive Rocks:
* Form from magma that cools and solidifies beneath the Earth's surface. This cooling process happens slowly, allowing for the formation of larger crystals.
* Have a coarse-grained texture (phaneritic).
* Examples:
* Granite: A light-colored, coarse-grained rock with quartz and feldspar crystals.
* Gabbro: A dark-colored, coarse-grained rock with pyroxene and plagioclase crystals.
* Diorite: An intermediate-colored, coarse-grained rock with hornblende and plagioclase crystals.
Here's a simple analogy:
Think of baking bread. If you bake a loaf of bread in the oven (like magma cooling underground), it will have a coarse, crumbly texture. If you bake a thin cookie on a cookie sheet (like lava cooling on the surface), it will have a fine, smooth texture.
In summary:
* Extrusive rocks: Cool quickly on the surface, fine-grained texture.
* Intrusive rocks: Cool slowly underground, coarse-grained texture.
