1. Cooling Rate:
* Slow Cooling: This allows more time for atoms to move and arrange themselves into an ordered crystal structure. Larger crystals form.
* Fast Cooling: Atoms have less time to organize, resulting in smaller crystals, even microscopic ones.
2. Magma Viscosity:
* Low Viscosity (runny magma): Allows crystals to grow larger as they have more space to move and aggregate.
* High Viscosity (thick magma): Limits crystal growth due to restricted movement.
3. Chemical Composition of Magma:
* Abundant Nucleation Sites: Impurities and pre-existing crystals provide starting points for crystal growth, potentially leading to more, but smaller crystals.
* Chemical Stability: The stability of different minerals in the magma influences their growth rates. Some minerals grow faster, leading to larger crystals.
4. Amount of Available Elements:
* Abundant Elements: Support larger crystal growth.
* Limited Elements: May lead to smaller crystals or even incomplete crystal formation.
5. Pressure:
* High Pressure: Can accelerate crystal growth by promoting diffusion of atoms.
* Low Pressure: May slow down crystal growth.
6. Time:
* Longer Time: Allows for more significant crystal growth, given other factors remain stable.
Examples:
* Intrusive Igneous Rocks (e.g., granite): Form deep within the Earth where cooling is slow, leading to large crystals.
* Extrusive Igneous Rocks (e.g., basalt): Form at the surface where cooling is rapid, resulting in smaller crystals.
* Porphyritic Rocks: Have a mix of large crystals (phenocrysts) formed during slow cooling and smaller crystals (groundmass) formed during rapid cooling.
It's important to note that these factors interact in complex ways, and the resulting crystal size is a consequence of their combined influence.
