Here's why:

* Fine-grained rocks have small grains. The definition of "fine-grained" means the individual mineral grains are too small to be identified with the naked eye. They are typically less than 1 millimeter in size.

* They require magnification. You'll need a hand lens or microscope to see the individual grains in fine-grained rocks.

Examples of fine-grained rocks:

* Basalt: A common volcanic rock with very small, often microscopic, crystals.

* Shale: A sedimentary rock formed from compressed mud, with tiny clay and silt grains.

* Rhyolite: A volcanic rock with a glassy texture, often containing very small crystals.

Contrast this with coarse-grained rocks:

* Granite: A common igneous rock with large, easily identifiable crystals.

Let me know if you have any other questions about rocks!