Coarse-grained phaneritic rocks:
* Crystal size: Minerals are large enough to be identified with the naked eye. They often have a granular appearance.
* Visibility: The individual crystals are easily visible, often forming distinct grains.
* Example: Granite, gabbro
Fine-grained aphanitic rocks:
* Crystal size: Minerals are too small to be distinguished without a magnifying glass or microscope.
* Visibility: Crystals are not visible to the naked eye, giving the rock a dense, uniform appearance.
* Example: Rhyolite, basalt
In summary:
* Phaneritic rocks have large, visible crystals, giving them a coarse-grained texture.
* Aphanitic rocks have small, invisible crystals, resulting in a fine-grained texture.
The difference in grain size is primarily a result of the cooling rate of the magma or lava:
* Slow cooling: Allows for the formation of large crystals, resulting in phaneritic rocks.
* Fast cooling: Prevents crystal growth, leading to the formation of small crystals and aphanitic rocks.
