Here's why:
* Grain size is a key characteristic in describing rocks.
* Coarse-grained rocks have large, easily visible grains.
* Fine-grained rocks have grains that are too small to see without magnification.
Other terms related to grain size in rocks include:
* Medium-grained: Grains are visible, but not as large as in coarse-grained rocks.
* Aphanitic: Grains are so small they are not visible to the naked eye.
* Pegmatitic: Exceptionally large crystals, often several centimeters in size.
