1. Cooling Rate:
* Fast Cooling: When magma cools quickly (like when it erupts as lava), it has less time for crystals to grow. This results in fine-grained, extrusive rocks like basalt or rhyolite.
* Slow Cooling: Magma that cools slowly (deep underground) allows crystals to grow large. This forms coarse-grained, intrusive rocks like granite or gabbro.
2. Mineral Composition:
* Differentiation: As magma cools, different minerals crystallize at different temperatures. The heavier minerals sink to the bottom, while the lighter minerals rise to the top. This process, called crystallization differentiation, results in different magma compositions at different depths within the magma chamber.
* Assimilation: As magma travels through the Earth's crust, it can melt and incorporate surrounding rocks. This changes the magma's composition, leading to different igneous rocks.
3. Fractional Crystallization:
* As minerals crystallize from magma, they remove specific elements from the remaining liquid. This process, called fractional crystallization, alters the composition of the magma, leading to the formation of different igneous rocks.
Example:
Imagine a magma chamber containing basaltic magma.
* Slow Cooling: The deep, slowly cooling magma will crystallize into coarse-grained gabbro.
* Fast Cooling: If some of the magma erupts, it will cool quickly and form fine-grained basalt.
* Differentiation: The bottom of the magma chamber may be enriched in heavier minerals, leading to the formation of more mafic rocks like pyroxenite.
* Assimilation: If the magma assimilates some felsic (light-colored) rocks, the composition may change, potentially resulting in the formation of a rock like diorite.
In summary:
The same magma can produce multiple igneous rocks depending on:
* Cooling rate: How fast or slow the magma cools
* Mineral composition: How the magma's composition changes through differentiation, assimilation, or fractional crystallization
This diversity in igneous rock formation is a testament to the complex processes that occur deep within the Earth.
