What is the Difference Between Intrusive and Extrusive Rocks?

The main difference between intrusive and extrusive rocks lies in their formation process and location. Here are the key differences:

1. Formation Process: Intrusive rocks are formed from magma that cools and solidifies within the crust of the planet, while extrusive rocks are formed on the surface of the Earth from lava, which is magma that has emerged from underground.
2. Cooling Rate: Intrusive rocks cool slowly underground, allowing large crystals to form. Extrusive rocks, on the other hand, cool quickly at the Earth's surface, resulting in smaller crystals.
3. Crystal Size and Texture: Extrusive rocks usually have small crystals or are glassy due to their quick cooling, while intrusive rocks have larger crystals because of their slower cooling process.
4. Mineral Proportions: Both extrusive and intrusive rocks can be classified into four main types based on their mineral proportions: felsic, intermediate, mafic, or ultramafic. Felsic rocks are high in silica, while mafic rocks are high in dark minerals. Ultramafic rocks are the most dense and composed primarily of dark minerals.

In summary, intrusive rocks form deep underground from slowly cooling magma, resulting in larger crystals, while extrusive rocks form at the Earth's surface from quickly cooling lava, resulting in smaller crystals.

Comparative Table: Intrusive vs Extrusive Rocks

The main difference between intrusive and extrusive rocks lies in their formation process and cooling rate, which affects their crystal size and texture. Here is a comparison table highlighting the differences between intrusive and extrusive rocks:

Intrusive igneous rocks, such as granite and diorite, form when magma cools slowly beneath the Earth's surface, allowing large crystals to grow. On the other hand, extrusive igneous rocks, such as basalt, andesite, and rhyolite, form when lava cools rapidly at the surface, resulting in small crystals or even glassy textures.