Here's a breakdown:
* Fine-grained granite: Crystals are less than 1 millimeter in size, giving the rock a smooth, almost homogenous appearance.
* Medium-grained granite: Crystals are between 1 and 5 millimeters in size, making individual grains visible to the naked eye.
* Coarse-grained granite: Crystals are larger than 5 millimeters, and sometimes even reach 10 millimeters or more. This results in a very distinct texture with individual crystals easily identifiable.
However, there are exceptions. Some granite varieties, like pegmatites, can have crystals reaching several centimeters or even meters in size!
The size of crystals in granite is influenced by factors like:
* Cooling rate: Slower cooling rates allow crystals to grow larger.
* Amount of silica: Higher silica content typically leads to larger crystals.
* Presence of volatiles: Water and other volatiles can enhance crystal growth.
So, while the general range is 1-10 millimeters, you can encounter granites with much smaller or larger crystals depending on the specific geological conditions.
